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Oral History Transcript — Dr. Ralph Bray

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Interview with Dr. Ralph Bray
By Paul Henriksen
At Purdue University, West Lafayette, IN
May 14, 1982

 
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Ralph Bray; May 14, 1982

ABSTRACT: Born in Russia 1921, moved to New York 1922; Brooklyn Polytechnic Institute (physics); Purdue University (Ph.D.), 1942- 1949; works teaching military students, 1943-1945; cyclotron and beta ray spectroscopy projects (related to Manhattan Project); Karl Lark-Horovitz as blanket-adviser; semiconductor project with Ron Smith; spreading resistance measurements; Edward Teller, John Bardeen, William Shockley; the self-transistor effect (Bell Laboratories); third electrode work by Seymour Benzer, 1949; semiconductor project; comments on Lark-Horovitz. Also prominently mentioned are: Joseph A. Becker, Walter Houser Brattain, Bill Fan, Arthur Ginsburg, Vivian Annabelle Johnson, Bernard Kurrelmeyer, Robert Green Sachs, Isidor Walerstein, Hubert J. Yearian; American Physical Society, Brooklyn College, Manhattan Project, and United States Army Signal Corps. Interview conducted as part of the International Project in the History of Solid State Physics.

Transcript

Henriksen:

Shall we start at the beginning? I have a few questions on your early background.

Bray:

Whatever you want.

Henriksen:

I know you were born in Moghilev, Russia on September 11, 1921, but that is about all I know about your early background. What did your parents do for a living?

Bray:

Well, we all left Russia when I was a year old. My father was a barber and when he came to the United States he went to work for a hairdresser, a women’s hairdressing establishment.

Henriksen:

Why did they leave Russia?

Bray:

Poverty. The whole family on my mother’s side was leaving. Her two brothers had left during the war to escape fighting for the Czarist Army and they had come to this country. There is a long story about that, which is probably irrelevant to you.

Henriksen:

Well, maybe if we have time at the end.

Bray:

They gradually sent for the various sisters who were married or unmarried. The story my mother tells me is that there was very little food and they had to find bottles and bring them in for deposit to try to get enough milk for me. So everyone who could at that time, left and so that is how we came over here, directly to Brooklyn.

Henriksen:

Do you have other brothers and sisters?

Bray:

No, I was the only one at that time. My sister was born in the United States about six years later.

Henriksen:

What kind of education did your parents have?

Bray:

Neither one of them, I think, finished grade school. There wasn’t much opportunity in a small Russian village to get an education especially if you were Jewish.

Henriksen:

When you got over to the United States and you were growing up here, did you have access to books?

Bray:

Sure, the public library. The New York Public Library and commercial bookstores, but most of the books came from the New York Public Library.

Henriksen:

Did you read a lot?

Bray:

Yes.

Henriksen:

What kind of books?

Bray:

What fascinated me most was the precursor of science fiction, which were the fairy stories, the Blue Book Grimm’s Fairy Tales and things like this that were very imaginative. Things like Uncle Tom’s Cabin, Tarzan of the Apes, and all the boys’ books. What else? That’s all that comes to mind right away.

Henriksen:

Did your parents encourage your reading?

Bray:

Yes.

Henriksen:

Did they encourage your education too?

Bray:

They did, All the way. That wasn’t true of all my relatives. In my family it was complete support and never any question that I would go on to college and graduate school.

Henriksen:

Did they have an idea of what they wanted you to do?

Bray:

No.

Henriksen:

They left that up to you?

Bray:

There was never really much discussion of it. They encouraged it, but there was never very much intellectual discussion of it.

Henriksen:

Were there any secondary school teachers that made a big impression on you?

Bray:

Not really. The physics teacher certainly wasn’t inspiring and I remember when I had to choose between, choose my first science course, chemistry, physics, or biology, and I picked physics because everyone else was picking,... Okay, I took elementary biology, which was required, and I hated it. It was pure memorization. And so that automatically pushed me away from biology and I had a choice of chemistry or physics and very few people were taking physics and I always liked to go in the opposite direction to the crowd so I chose physics. And in fact I was going to major in chemistry or physics, when I went to college and I found that everything I liked in chemistry, first year chemistry, was really advanced physics—

Henriksen:

The processes behind

Bray:

All the atomic stuff and everything else, so I ended up in physics. I think the influence on my physics was much more in college than in high school.

Henriksen:

Were you interested in science all the way?

Bray:

Not so much science, the science that you had in elementary school was how bells work and things like this which is absolutely boring. I was more interested in questions of astronomy and what stars were like. You know just pure type of daydreaming. You wonder what is out there in the sky. What is magnetism? What is a star? What is the world like? I gradually discovered that physics was the closest thing to be concerned with those questions.

Henriksen:

Did you plan on going to college right from the beginning?

Bray:

It scared the hell out of me because I was worried when I was in grade school that I’d flunk out of high school. And I was worried in high school about what college would be like. I didn’t know anyone who had been to college in my daily acquaintance, so it was all a big mystery to me, but there was never any real alternative path that I would think of. So it was a natural thing to continue on even though it was a complete mystic void to me,

Henriksen:

Did you have any goals when you started college? Did you have any idea of what you wanted to be when you had finished your education?

Bray:

Probably none at all, no. Except probably that I was interested in science and I might have been interested in social sciences except that I really didn’t know what they were, and didn’t know that it was a viable option.

Henriksen:

Well it is interesting that you would be that inclined toward I guess the hard sciences when the family background wouldn’t have been in that. Was it just from your speculations about what the world was like?

Bray:

I guess it was from just interest in things that were imaginative, that stimulated my imagination and pushed me in that direction. A lot of my own reading. I read the newspapers very attentively. I was interested in politics, of course. No, there was a lot of interest in politics at the time with the Depression and Roosevelt’s election and things that were going on in Europe, the rise of communism and fascism. So I was always interested in those things, but they seemed to me things that you read about in the newspaper, not something you did something about or studied, so I just took those things for granted. I guess I was surprised afterward to find that some people actually could use that interest to make a living, or to make a profession out of it.

Henriksen:

Why did you choose Brooklyn College?

Bray:

Well I was debating between Brooklyn Polytechnic, the engineering school and Columbia and I actually made some effort to go to Columbia. But Brooklyn, for one thing I went to Boy’s High which seemed like a good school and I also preferred a school—I wasn’t particularly interested in girls at that time and Boy’s High seemed like an attractive place.

Henriksen:

Was that one of the more technical high schools in New York?

Bray:

You are thinking of Brooklyn Tech which is an all boys school and also technical and Boy’s High was probably the best known school in Brooklyn for its academic rating, but it was not technical. I had to travel quite a distance to get to it, but after four years, I decided I wanted to go to a coeducational school and that was one reason that I didn’t consider Brooklyn Polytechnic Institute, and Columbia of course was much more expensive and much further away, so I thought I would start at Brooklyn College and see what it was like, and then when I had the option of going to Columbia I already had my friends at Brooklyn College and so I decided to stay there. It was a very pleasant place and the tuition was zero. The first semester I had to pay 50 cents towel fee for the gym. And my biggest expense was breakage f cc for chemistry which was something like $10 for the semester.

Henriksen:

Pretty reasonable.

Bray:

Pretty reasonable. Quite a difference from now.

Henriksen:

What was your bachelors degree in? Was it physics?

Bray:

Physics with minors in chemistry and math. Benzer by the way was also at Brooklyn College.

Henriksen:

At the same time?

Bray:

Yes, He was a year ahead of me.

Henriksen:

Did you know him when he was there?

Bray:

We overlapped in something called the advanced lab, which you could take for two years and where you did independent experiments. There was very little written up. You just about had to tell the professor what you wanted to do and he sort of directed you to the cabinets to what equipment you might use. And Benzer and I were there and two other guys named Ginzbarg and Cassen, And all four of us ended up at Purdue, at different times, we didn’t all come at the same time.

Henriksen:

I have come across the Ginzbarg name. Alan Ginzbarg?

Bray:

Arthur.

Henriksen:

Arthur. I must have just seen A. Ginzbarg.

Bray:

He worked on the semiconductor project too, but his background or orientation was theoretical. He ended up doing a thesis with Schwinger, master’s thesis.

Henriksen:

So he was one of the... There weren’t that many people doing theory at Purdue at the time.

Bray:

Schwinger was here for a year and he quickly jumped to Harvard, I guess to work on the radiation project. Bob Sachs was here and Vivian Johnson.

Henriksen:

Sachs was only here for about a year also.

Bray:

Right, so I had a course with Sachs. I did not have a course with Schwinger. The others did who were here a year before me. My main contact with Schwinger was in the ping pong room.

Henriksen:

Did any undergraduate teacher at Brooklyn make a big impression on you?

Bray:

Yes, there was a man named Bernard Kurrelmeyer who really influenced most of the physics majors who went to graduate school from Brooklyn College.

Henriksen:

What was his area? Did he have a specific interest in research?

Bray:

There was no research at Brooklyn College in those days. People were teaching 16 hours a week. He may have done some research in Columbia. His wife was at Columbia and he had a background in I think specific heat measurements. He had spent a post—doctoral year at Leyden. So there was actually no contact with research except in this advanced lab course. But I had him for four courses. He wasn’t a terribly good teacher, but he was an inspiration to many of his students to go on into physics and he was very interested in his students. There are a couple of other people there who also had influence. Are you interested in their names?

Henriksen:

Sure.

Bray:

There was William Rarita, he was famous for a paper with Schwinger and a man named Mais and another named William Green and that was a very nice atmosphere.

Henriksen:

How many people did they have on the faculty in physics? A lot or 10 or 20.

Bray:

I would say under 10, about 10.

Henriksen:

Did you decide on doing semiconductors at that time?

Bray:

Not at all, I never heard of it. The only decision I had to make was whether to go to graduate school. Also about the time I decided to go to graduate school was the time of the draft.

Henriksen:

Did that cause problems?

Bray:

Well there was a question of what would happen. Would I be drafted? Would I go to graduate school? It was up in the air, No the problem was which graduate school I would go to, And Kurrelmeyer was our advisor in this and I had applied to Wisconsin, Purdue, Harvard, and Cornell. And the only two places to respond were Harvard and Purdue and the response came on the same day and I picked Purdue for two reasons. Kurrelmeyer recommended it. He said I’d probably be better off at Purdue. And the second reason it was further from home. And within the week that I got here, I got an offer... Oh, the other reason was this, that Kurrelmeyer gave, Harvard’s offer was a pure fellowship, $600 a year. Purdue was a teaching assistantship and he and the other people at Brooklyn College said if you don’t have teaching experience you’ll have a very difficult time getting a job afterwards, so it would be better to come to Purdue and get the teaching experience with the teaching assistantship rather than with a pure fellowship at Harvard, I think today that judgment would be completely reversed.

Henriksen:

Oh really?

Bray:

Sure, how many of us get jobs based on teaching as a graduate student? The issue never comes up.

Henriksen:

That is true but I found when I started that I learned a lot more about physics when I actually had to teach it.

Bray:

Of course, that is true, but that is a better argument than that you did it so you’d be better able to get a job. Besides, who was getting jobs in physics in those days? It was crazy. Well the other thing I might point out was that when I decided to go, I made the decision to be a physics major when I was in high school, physics and chemistry, and really all my friends——there was a group of us who all worked together in the math office. (Somehow the math department was an area where people of common interest gathered.) They provided a room for it and most of my friends decided to go in to accounting and went to City College in accounting because they thought they’d never get a job in the sciences. There was a feeling that there were no jobs in physics and for Jews it could be especially difficult. Well what they didn’t anticipate, (at least two of these I remember did graduate with a bachelor’s degree in accounting and then switched, one to medicine and one to physics), was that by then the war was over or close to being over and the situation as far as science was completely turned around. I guess I was naive enough and not worried about money to ever consider that as a factor in what I should be studying, so I owe my parents that thanks for never raising the issue of how I would make a living. It is an important factor I guess. So I picked Purdue because I had a teaching assistantship and there were two Purdue people already here, Ginzbarg and Benzer and the recommendation of Kurrelmeyer.

Henriksen:

Did you talk to Benzer and Ginzbarg before you decided? Did they tell you about Purdue?

Bray:

I think I had to make my decision in the week that I got the invitations for the assistantships. I made my decision without them, but I saw at least one of them that summer before I came down to Purdue, but by then I was committed.

Henriksen:

They encouraged you then I assume?

Bray:

They didn’t discourage me.

Henriksen:

This is 1942?

Bray:

I came here in September of 1942. I believe Benzer came in January and Ginzbarg came the September before.

Henriksen:

So you taught for about a year before you got the research assistantship or were you teaching and doing research at the same time?

Bray:

Soon as I came here there was a big teaching load due to the Army and the Navy sending students here for a year’s training, so we all got drawn into that program and we were teaching 12 to 15 hours and getting paid a little bit extra for it. That didn’t happen the first year. It was true by the second year.

Henriksen:

So you started on the semiconductor project in late 1943?

Bray:

Something like that. No, in fact my first project was on the Manhattan project. There was a small effort on the Manhattan Project involving the cyclotron and I remember I was not told what it was. I was just asked to build an oscillator, bread board oscillator, that was probably during the first year I was here [1942]. By the end of the first year that project just disappeared. Everyone left, And what happened was that the major people on it and a couple of the graduate assistants who were here ahead of me all moved to Los Alamos and I knew very little about it because it was supposed to be a secret and I guess it was. And one of those students was actually one of those who died in one of those accidents with one of the reactors at Los Alamos.

Henriksen:

Vivian Johnson mentioned his name.

Bray:

Daghlian

Henriksen:

Perry Daghlian.

Bray:

There was a big flux of graduate students in and out. And then we became aware of the semiconductor project and a whole bunch of us joined up with it.

Henriksen:

That is what I am interested in, how you actually got started on that project.

Bray:

We weren’t even told what the project was. That was still secret. We had to wait for clearance. So I was put in a room in the basement without windows, with almost no information and told to look at—take spreading resistance measurements.

Henriksen:

So you started that as soon as you were on the project?

Bray:

Right. They told me how to make these tungsten whiskers by an electrolytic etch process and then making point contacts to germanium. If I needed anything I was supposed to knock on a door on the second floor and ask for it, but I didn’t know what to ask for and I had no contact with it and so it went the first year. I remember I went back to Brooklyn College at the end of the first year to talk to my professors there and I was ready to do anything to get out of here. It seemed very isolated to be here with almost everyone I knew of my age in the Army. It was very strange to go to New York and be 22 or 23 and be about the only one who wasn’t in uniform. It was a very strange feeling. It was okay as long as I was at Purdue because everyone else here was in the same boat, but I didn’t see my work going any place or what I would be getting into. Eventually I got more involved in the semiconductor work,

Henriksen:

Did you have a choice—Did they look at that as your thesis work at the beginning?

Bray:

It had nothing to do with my thesis. Everything was oriented—-both teaching and research—toward the war. There was a possibility of an experiment when the Manhattan Project left. In fact I was assigned to work was given a room with some very old equipment, just a massive magnet and other things, to work on beta ray spectroscopy.

Henriksen:

Was that the Ross magnet or a smaller one?

Bray:

I can’t remember. I know the Ross magnet eventually was used for Ball effect. I can’t remember. Was it beta ray spectroscopy? Yes. That was what I was interested in. I was very interested in the subject, but I was just thrown into a room with no advisor. Nothing much happened and before I ever got started I was shifted up into the semiconductor effort.

Henriksen:

It was all a matter of Lark—Horovitz assigning you to a...

Bray:

Be assigned me to look into the question of spreading resistance and to set up and make spreading resistance measurements. But that was certainly the second, at least the second year. Because I remember even in the first year I participated in group discussions on the operation of the cyclotron and in fact I gave a talk on the theory of focusing the particle beam and shimming the magnet. I remember learning a heck of lot from having to prepare that material. And I guess that was part of my involvement in the Manhattan Project without my knowing it. In fact I have a little button someplace, showing I was a member of the Manhattan Project. I didn’t know until the war was over and I got this button.

Henriksen:

After the war.

Bray:

Yes.

Henriksen:

You say you had no advisor. Was Lark—Horovitz sort of a blanket advisor for everybody, or did you actually have anybody over you?

Bray:

Be was a blanket advisor for all the graduate students and then we established informal contacts with the other professors on the project. I guess you know who they are, but maybe from my viewpoint they would appear different from what you have from others. There was Ron Smith, Yearian, Walerstein, and Johnson and every student was responsible to Lark—Horovitz, not to anyone else. That persisted for years afterwards, not just on that project——that was just the way he operated, but one established informal liaisons with other graduate students and some of the professors and the person who was most helpful to me was Ron Smith.

Henriksen:

Be had a background in nuclear physics, didn’t he?

Bray:

I also talked—— I guess he did. People who did not go off with the Manhattan Project were all pulled into the semiconductor project, but that was a segment of the Radiation Lab. I believe Pennsylvania got silicon and we got germanium.

Henriksen:

Yes, I have been digging into how that was divided and why Lark— Horovitz chose germanium. So you had most of your discussions with Smith, or want to him when you had a problem?

Bray:

Right, because the first thing we found was that spreading resistance was much less than one would predict from the resistivity.

Henriksen:

Smith wasn’t a theoretician was he?

Bray:

No, but he had the best— Be was an experimentalist. But he had—— Well Vivian Johnson was the theoretician and Walerstein did the Hall effect measurements, so the people who did the Hall effect measurements— There were a bunch of students who were associated with him. Yearian was probably the best experimentalist, but he just didn’t interact with the students. Smith was the one Benzer and I would go to if we had anything to talk about.

Henriksen:

Did you work very closely with Benzer?

Bray:

Not really, no, Benzer was the kind of guy who liked to work by himself. He’d come in to work at two in the afternoon and work until midnight or two or three in the morning. So he was just a late worker in that sense.

Henriksen:

That sort of fit in with Lark—Horovitz’s style.

Bray:

In a way.

Henriksen:

He liked to start at about 10 o’ clock in the morning and go until 2 a.m. Did the way Lark—Horovitz worked pressure at all? Did that affect how you worked?

Bray:

No, I had my own schedule. The pressure from Lark—Horovitz was that: if he saw you around when he was around, then you were working, if he didn’t see you around when he was around then you weren’t working. You were expected to be there seven days a week and if one of us wanted to go to Chicago for a day during the war we just about had to ask him for permission.

Henriksen:

So he was really the dictator of the group.

Bray:

Very much the driving force.

Henriksen:

Did you find that— Some people found that stimulating.

Bray:

No it wasn’t stimulating. It was a little bit frightening. It was intimidating. It wasn’t stimulating because as far as my research went there was never any stimulation.

Henriksen:

Did he ever talk to you about the research?

Bray:

Aside from providing the initial motivation which I can tell you about. The trouble was the research always went in the direction that was different from anything he anticipated and so he never really discussed it very much with me.

Henriksen:

Tell me about the motivation.

Bray:

The motivation was that one didn’t know for sure at that time what a semiconductor was, why it had high resistance. There was some work——I think by a guy named Busch in Zurich, Switzerland which suggested that there was— (I was aware without knowing the literature. I had no courses in semiconductors or solid state at all, I was just thrown into it.) I was aware that there was a question of what a semiconductor was, whether these materials were semiconductors, and if their high resistance was due to localization of resistance at grain boundaries, (You see there were no single crystals at that time,) with low resistance, low resistivity material in between the grain boundaries. The idea of our experiment was to use spreading resistance as a probe to measure the local resistivity and to see if the local resistivity matched the bulk resistivity measured by putting on two end contacts and measuring the resistance of the sample.

Henriksen:

Lark—Horovitz mentions in one of his letters, that he thought the effect was due to grain boundaries. [See Lark—Horovitz to Harper North, Nov. 27, 1944.]

Bray:

And in fact in some samples the resistance was high because of grain boundaries, but in general that was not the point.

Henriksen:

That was more of a masking effect that the actual mechanism.

Bray:

Right. There are lots of things that can happen. These were n—n junctions——junctions between n and n material which did not appear in p type—— so in p—type these grain boundaries did not have high resistance. So a lot of my work was with p type and there the resistivity was measured by the spreading resistance being smaller by factors of 10 to 100 than we’d expected from the bulk measurements. And that was the big mystery! And we ran through lots and lots of samples and it happened in all samples. The exact numbers were quite variable from sample to sample.

Henriksen:

Is it just the difference between the materials or was it due to... Why are the n and p types different in that respect?

Bray:

N—type material develops a p layer on the surface automatically so you could think of an n—n barrier as having a p layer in between. So it is sort of two p—n junctions back to back giving the high resistance; whereas, p material on the surface didn’t particularly rectify well because it did not have this inversion layer. N—type material had the inversion layer. So it automatically gave good rectifying contacts when you had a point contact on there. And p-type didn’t give a good rectifying contact because it was much more closely ohmic or had other strange characteristics.

Henriksen:

I was just trying to separate out whether that was due to the way it was prepared, since it was polycrystalline or is it just a quality of being a p type... If you have a pure p—type semiconductor does that still hold? Is that still the case or is it just because the sample is polycrystalline?

Bray:

There are probably many factors, but one factor was that if you had pure n—type and pure p-type, the n-type will give good rectifying contacts and p-type won’t at least with the surface treatments that we then had available. And the reason is that n-type had the inversion layer which we didn’t know about at that time, if we knew about an inversion layer we’d know about p-n junctions and we’d know about all this other stuff. We didn’t know at that time why n—n barriers, grain barriers would have the high resistance and p barriers wouldn’t be, and that all came out sequentially in later papers. Some of it wasn’t explained until two years later. So I want to distinguish between what we knew then and what we knew after.

Henriksen:

How did you learn about semiconductors if you were just starting on a project and had no courses?

Bray:

I found some books in the library. There was a book by Wilson on metals and semiconductors I remember, a paperback, Cambridge tract or something like that, I can’t remember. There was Mott and Gurney’s book which was much harder to read. Was it Mott and Gurney or Mott and....?

Henriksen:

There is a Mott and Gurney and a Mott and Jones. I get the two mixed up.

Bray:

Well, whichever. I don’t remember. What else? There were almost no seminars here. There was no effort to really teach us and discuss these things, which they should have done.

Henriksen:

Was that because there were too few people to give the seminars or was it because people were looking to crank out the results for the Radiation Lab?

Bray:

That could be. The emphasis was on crystal growth and that part was run by Whaley——to get better crystals—and they tried putting in all kinds of impurities and then——

Henriksen:

They tried almost everything.

Bray:

Right. Benzer was interested in looking at the rectifying contacts. I was looking at the spreading resistance, so his interest was in whether you could get a high resistance in the reverse direction. I was interested in what determined the resistance in the forward direction and that was a stupid dichotomy because it was the thing as a whole that was important afterwards.

Henriksen:

But you were both assigned to the...

Bray:

It put us, not so much in competition, but we felt that one realm belonged to him and the other belonged to me. Smith made measurements of high frequency characteristics of these rectifiers, because they were to be used as mixers. So I guess the answer is the urgency of getting these things as devices.

Henriksen:

And most of the work here was device oriented wasn’t it?

Bray:

It was directly oriented toward devices because of the urgency of the Radiation Lab at MIT.

Henriksen:

There were certain efforts that were on the theoretical side with Vivian Johnson.

Bray:

The more basic work was the Ball effect measurements and of course you had to characterize the material if you found different things on different samples. You had to know what to correlate it with and Vivian Johnson did some of the work in analyzing the Hall effect and resistivity and finding out what the mobility was and temperature dependence and there was some work with Victor Weisskopf and Esther Conwell on impurity scattering and that was also with the motivation of understanding the transport properties.

Henriksen:

So the emphasis was clearly on the devices and actual experimental basic...

Bray:

We were split into two groups, those who did Hall Effect, resistivity and thermoelectric power measurements to characterize the material as a semiconductor and others of us who worked with the point contacts for the device applications.

Henriksen:

Were the professors, Smith, Walerstein, and Yearian in about the same boat as the students as far as what they knew on semiconductors at the beginning of the project?

Bray:

Probably, because no one had a background in it, There may have been lectures on it in the beginning before I joined and they might not have been repeated them, Bob Sachs was here and he wrote some monographs on it and Bethe wrote some monographs when he was at Cornell, so quite likely there were some lectures on it, but I wasn’t exposed to it because of the phase lag in my joining the project, So those of us who joined in the second or third year of the project were not exposed to it from the beginning.

Henriksen:

So you really were in a worse position.

Bray:

Except that we did get together every week and report on what we were doing.

Henriksen:

Would the whole group get together?

Bray:

The whole group, so you sort of picked things up from the discussion, Lark—Horovitz would always report on things that he heard when he went away to other labs.

Henriksen:

Did he also keep you abreast of what was in the various journals? Other people have mentioned that he read everything.

Bray:

Yes, You’d see him frequently in the library. There’d be some desk piled up with books and you could see that he was looking through some of these things and maybe he was looking up some of the anomalies that I was finding on the spreading resistance, but we just never talked much about it because he never was able to get involved in my project. And I did get involved with Smith and he seemed sort of angry that I was reporting to and discussing things with Smith and even getting off on tangents on the problem and I think he rebuked Smith for influencing the course of my research.

Henriksen:

Well that sort of fits from other things I heard about Lark-Horovitz. It must have been an incredible atmosphere to try to work under.

Bray:

It didn’t affect me too much because, maybe I was lucky I was always finding things that were different from anything he expected, so there wasn’t much he could do, With other people that he got more heavily involved with, the tension and the interaction were much much stronger.

Henriksen:

Yes, Sachs mentioned that. He mentioned that as a reason he left after only a year, just couldn’t take it.

Bray:

Okay. Also there was some work here with Fritzsche after the war and even some lawsuits eventually, but there was very strong interaction and pressures as to which direction the work should go. Also the infrared aspect which came towards the end of the war which was involved with Meissner and Fan, a tremendous interaction. He was also involved closely with the radiation damage, but he never understood what I was doing so he never bothered me very much and I guess I was never really aware how lucky I was perhaps in that respect. On the other hand it also meant less involvement and less direction, It could be one of the reasons that we missed—We missed two things. We missed out on publications because he was very loathe to publish anything and we missed out on the possibility of inventions.

Henriksen:

He sort of thought that abstracts at meetings were acceptable conditions of priority I guess.

Bray:

Right. He seemed to be afraid to publish because it might be wrong, it might not be the whole truth.

Henriksen:

That must have been frustrating, Did that hold up many of your publications?

Bray:

Oh yes. I didn’t start publishing and I didn’t do much until after I got my degree and in subsequent years the lack of publications delayed my promotions, because it became a habit also. It took me a long time to learn that publications were necessary. In fact the pressure to publish did not come until new people arrived here like Fan and you saw them writing up things and publishing them. You said to yourself, “Oh is that what you do?” Wasn’t it enough to just do research? Write progress reports? See, we wrote progress reports for the Signal Corps after the War and gave these ten minute APS abstracts. As far as I knew then, that was sufficient.

Henriksen:

That would be a problem starting graduate work in a war atmosphere.

Bray:

That was the other thing.

Henriksen:

Communication wasn’t promoted.

Bray:

The war was so much more a driving force than anything else. Besides you couldn’t publish. It was secret.

Henriksen:

All you could do was write up the short Rad Lab reports and mail them off.

Bray:

But one of the things I must say was that he let us write our own reports which is possibly a failure on my part with respect to the students, I don’t give my own students the chance to write their own reports and go through all the stages of learning how to write simply by the experience and practice.

Henriksen:

Let’s look at this letter for a moment. [Lark—Horovitz to Harper North, Nov. 27, 1944.] He mentions in his discussion the grain boundaries idea. How far off was he from what was going on? He mentioned the grain boundaries were a part of the resistance anomaly, but not the real cause.

Bray:

Well what ultimately happened was that the grain boundaries were a diversion from the truth. They were present in some materials, but it turned out that germanium and silicon were real semiconductors. Their temperature properties— [A lot of that (grain boundary effects) was reported by the work in Switzerland.] You know in science there are many false paths that you get involved in and the whole path of grain boundaries was a false path. Those were accidental features and not the true path of semiconductors and it was necessary to get away from those, so you know there were...

Bray:

There were two approaches. One was to use the spreading resistance and Smith made measurements of these samples at high frequency because then if there were grain boundaries they would be shorted out, capacitatively shorted, but all that in the long run was a very uninteresting element of semiconductors. Because the real physics was in the single crystals which eventually developed or those portions of the sample that you could work on that weren’t influenced by grain boundaries; and then the spreading resistance anomaly was a real effect which led eventually to and tied in with the transistor.

Henriksen:

Did it really take the single crystals to make semiconductor work take off? Was it possible after that to actually see things?

Bray:

That was almost essential. You could look at the first samples I got under the light after you etched them and they had dozens of different reflections which meant that every section of the sample presented some different grain. And so you never knew what you were measuring. It was a complete mess.

Henriksen:

So the material was relatively pure. It was just the polycrystalline nature that caused the problems. It was probably worse when you had dirty polycrystalline material to try to do anything with. Did you ever discuss the spreading resistance with visitors to Purdue?

Bray:

Sure. Well there were people who came here like Teller, Lehovac, the Bell Lab group, Bardeen, Shockley, and others some from RCA (Rose and others). I guess you have a better list of visitors who came here. There were people who came here from...

Henriksen:

There were consultants who came here for longer periods.

Bray:

Weisskopf.

Henriksen:

Yes, Weisskopf. Nordheim?

Bray:

Nordheim. I didn’t meet all of these people okay? It sort of depended on when they came with respect to my getting started and beginning to find results, because most of the results I found on spreading resistance were.. Well if I came here in 42, I probably didn’t get on the project until late 1943 and then I was by myself for a half a year and so if I started getting in on things in 1944 that was sort of the last year before the war was over.

Henriksen:

Karl Herzfeld was here too.

Bray:

I don’t think I ever met him, But I remember Teller, There is a nice story about Teller, Benzer was showing him some of the point contact work, he didn’t know how much Teller knew about this, so he said, “At what level should I tell you about it?” And Teller said, “Assume that I am infinitely ignorant and infinitely intelligent,” and I still use that story when my students give talks. They should assume that the person they are telling it to doesn’t have any background in jargon and if you explain it they can understand it.

Henriksen:

Something to shoot for that doesn’t get approached too often.

Bray:

And then of course Shockley and Bardeen and Brattain and Pearson and some other people came here from Bell Labs, I can’t remember for sure how much of that was during the war and how much was after.

Henriksen:

There is a list in the back of Lark—Horovitz’s Final Report that mentions all the people that visited during the project.

Bray:

You want to know if I had contact with any of them?

Henriksen:

Well if anything leaps to mind as significant. Were they able to tell you anything about the spreading resistance?

Bray:

I do remember one guy named Lehovac who came here from Sperry and he came here before and after and I remember his remark, because he said, “You had this effect all the time, if only I had understood it when you told me about it.” [Referring to the final report] Well I certainly remember some of these people, Woodyard, Becker from Bell Labs and Seitz, Weisskopf, Park Mi 11cr.

Henriksen:

Did they come for a day or two to discuss questions?

Bray:

I suppose so yes. We’d show them around the lab and tell them what we were doing. Yes I remember the visit of Shockley and Morgan and telling them about my work.

Henriksen:

That was after the war was over.

Bray:

What happened was that the spreading resistance——that was sort of a mystery——and no one understood it and so I wasn’t pushed forward, pushed in front to talk about this very much, Of greater interest was the Hall Effect and the analysis of it and the high back voltage rectifier and my stuff, being a mystery, wasn’t really pushed forward so I did not get to interact as much with these people. Technologically it turned out to be the most important thing if it had been explained and understood because what really entered into it was the whole principle of minority carrier injection.

Henriksen:

Now Hall effect measurements that told you about the number of carriers were done after the minority carrier idea had been expressed.

Bray:

Start again, which Hall effect measurements?

Henriksen:

The ones on the high back voltage units, that where showing the anomalous resistance.

Bray:

The surface Ball effect measurements or the bulk Hall effect measurements? Let’s clarify this. The Hall effect measurements in bulk at low fields were done by Walerstein and the emphasis was on analyzing the mobility, number of carriers, and temperature dependence. Then Benzer did Hall Effect measurements with point contacts on the surface to find out what was happening around the spreading resistance.

Henriksen:

Oh I see. So Benzer looked at spreading resistance from the surface effects?

Bray:

To see if it was a surface effect. Because Smith was measuring anomalous capacitance and he and Smith were talking about the possibility that there was this layer on the surface that was different from the bulk. I don’t know if they used the concept of an inversion layer. They might have, but the capacitance was such as if the effective contact area was much larger than the actual physical area, okay, so it suggested that the metal contact was making contact with something else which in turn was determining the capacitance with respect to the substrate. Are you with me on that?

Henriksen:

I think so.

Bray:

Okay, because I can draw a little picture.

Henriksen:

That might help.

Bray:

What I am trying to say is that if you have your bulk material and you put your metal contact down like this the capacitance that you measured was of an effective area much bigger than the physical contact, if you want to choose to call it an effective area. So you could consider that there was a much bigger region and that this was making contact with and the capacitance was between this and this. [Refers to the diagram.] As it turned out eventually of course that was the inversion layer.

Henriksen:

The idea of spreading resistance came from the field seeming to be spreading out from the point contact.

Bray:

Spreading resistance was an older concept, a standard concept in the literature for electrostatics. Purely a geometrical effect, with the current from the point contact flowing out radically. It’s just a boundary value problem for such a distribution, so if this is a contact infinitely far away, the resistance of a point——. Well this is a technique used in the oil field business to measure the resistivity in the vicinity of the earth. You put a contact down and the earth far away is the other contact and so the spreading resistance due to the lines of flow is e/2ta where a is the radius. So the idea is that most of that resistance is in the region where the current is most concentrated and so it is a measure of the resistivity at the probe in this local area.

And you could imagine that the fact that the capacitance here is too low suggested a high effective contact area. That same argument might be carried over to why the spreading resistance was too low. That there was something there. But the tack we followed was a little bit different. We thought it might be the high field due to the high current density and so the thought occurred to Smith and myself that we should start with the bulk material where there was no high field and put on high voltage and see if the resistivity of the germanium was field dependent. Eventually we got away from the spreading resistance discovery to look at a uniform material with uniform current lines and see what the field dependence of the resistivity was. We found there too that the resistivity decreased with electric field, And so we made the connection in both cases—-the main reason for the low spreading resistance was the high field, but we didn’t know the origin of that high field effect on the conductivity, and so we were looking into mechanisms of field dependence of the conductivity and it is in that context that we talked about it at these meetings.

And then I decided to do Hall effect measurements and see if it was the mobility that was changing or the carrier concentration that was changing and that was a bulk Hall effect measurement with pulsed high electric fields and that was different from the DC Hall effect measurements of the surface by Benzer, But those were essentially two different lines of approach that we took and we began to find from the Hall effect that actually— —the Hall coefficient was changing, suggesting there was an increase in the number of electrons.

Henriksen:

Now was this before or after...

Bray:

Well I think I recorded those Hall effect measurements in the conversation, I either gave it at that meeting in Washington, or we could look that up and see if that was the subject. Let’s check that, [Referring to Phys. Rev, 74 pt. 2, p. 1218,] Dependence of resistivity of germanium in electric field,’ constant field pulses. “To determine how far the field changes the number of carriers or their mobility, the Hall effect measurements using these pulses have been started.”

Henriksen:

And this is the APS Meeting in Washington in April of 1948.

Bray:

And this is what scared the Bell Labs people, because they realized I would surely soon interpret this effect as a minority carrier effect.

Henriksen:

This is after they had seen, actually had demonstrated the transistor in December of 1947 and before they announced it in June of 1948.

Bray:

You see at this time Benzer was doing photovoltaic measurements, shining light on point contacts and influencing the current in the back direction. So it wouldn’t have taken much if we were changing the carrier concentration by these high fields to put an emitter down and bias it in the forward direction and see if that would influence the back resistance of a collector like the light did to the back resistance—the resistance in the back direction—and then you would have the transistor, but we never at that time made that jump. The other factor is Seymour Benzer was interested in the possibilities of a triode. He talked about this and I simply didn’t think so much in terms of devices. There was never an emphasis in the academic world in terms of making devices. I don’t know why Seymour thought about it, but I didn’t. And it wouldn’t have occurred to me that a triode might even be a worthwhile endeavor.

Henriksen:

Bob Sachs mentioned that he had, or Purdue had a pn junction rather early. Sort of a natural one that just occurred in the making of the material.

Bray:

In all of these materials we had pn junctions as well as nn and pp junctions, okay? And I played around with the pn junctions and found that I could put a point.,. Well I’ll back up... Benzer found that you could influence the pn junction with light, the literature already mentioned this. There were some papers by the Russians, Davydov on the pn junction, so we sort of had an idea what a pn junction was, After the invention of the transistor with two point contacts, I put a point contact near a pn junction and found I could get transistor action there too and I guess there was some problem with patent rights on the pn junction transistor because of these experiments.

Henriksen:

Sachs mentions that there was one here rather early, about when he was here in 1941. He had actually worked with pn junctions. But I wasn’t able to find any more substantiation on that.

Bray:

Since I came here in September of 1942 and didn’t get on the project until 1943 some time I would not know, My only contact with Sachs was that he gave a course in quantum mechanics.

Henriksen:

He claims too that he thought of making the transistor in 1941. He and Smith were working on that. They had the two electrodes on it and he said, “Why don’t we put a third one on there?” and he also said, “Well we will do that after the war.” How allegorical that is I don’t know.

Bray:

Could be. I never heard it mentioned, but that doesn’t mean anything one way or the other.

Henriksen:

When did you first notice that the spreading resistance was too low?

Bray:

Practically right from the beginning. No, it hadn’t been measured, My first measurements showed that it was very low, but what was even worse, there was a question of what you meant by spreading resistance since the current versus voltage was changing very rapidly. What you have in the forward direction is a contact potential difference that you have to overcome, so the current should not initially increase until the barrier is removed and then the current should rise and in the simple theory it will then rise linearly and that slope will give you the spreading resistance. Are you with me?

Henriksen:

Yes.

Bray:

Well it never went up linearly. It kept curving and curving and if you kept going it went vertical and the thing would sort of break down and so you wanted to avoid the breakdown because then you’d have to start working at another point. So you never knew quite what to call the spreading resistance. It was something that was a variable function of voltage, Of course the reason was that you were getting minority carrier injection which was decreasing the resistivity plus the fact that you were heating it locally and possibly causing it to run away, but we didn’t know any of this at that time.

Henriksen:

How did you actually know the spreading was too low, if the slope was changing and it was hard to tell what the spreading resistance meant?

Bray:

Well then I realized that it was too low at almost any point that I could measure once I got past the contact resistance. On some materials it wasn’t as bad as on others, but you’d sort of give a range of values, But it made it very difficult for a fresh student going into this to know just exactly what to do with this.

Henriksen:

That would be a knotty problem to try to sort out, especially right at the beginning. Why does the low spreading resistance only show up on the high back voltage units?

Bray:

The high back voltage units were the ones with the higher resistivity, and the ones that were not high back voltage had very low resistivity. They were much more impure, so the modulation of resistivity by minority carrier injection would be less significant. And they’d also burn out and not have the high back voltage characteristic, which was also something that we didn’t know about then. And in p type material we didn’t seem to get the injection effect so much, we had other problems. It wasn’t rectifying in general. The spreading resistance I guess was closer to what you’d expect for the material. And I guess one reason is that we didn’t have this pn junction and minority carrier injection, but then when we did the experiment with high fields in bulk it turned out that it was not a field effect, occurring uniformly throughout the material, but rather that our soldered contacts were injecting contacts, although we didn’t realize this initially. I guess eventually I made probe measurements along the sample and discovered that the cause of the decrease in the resistance was a field effect,—something progressing in from the one contact towards the other. That is something that would have been done independently of the discovery of the transistor, whether we would have thought of putting all this together into a transistor I don’t know.

Henriksen:

Certainly a difference between looking for a device and just examining properties.

Bray:

We were not looking for a device, We were interested in finding out. We were discovering phenomena and the phenomena were anomalous in terms of what we knew, which was not very much, and the thing was to try to figure out what was happenings. And I’d say that was the main motivation for me and I guess also to some extent for the others. I wonder if we had found transistor action as such whether we would have exploited it or made a big deal of it afterward. My feeling is we wouldn’t have because we did find all kinds of photovoltaic and photoconductive effects and after all the first photocells which led eventually to solar cells were also done here, okays They may have been done elsewhere, but they were certainly studied here. There was never any big push on those things. They were sort of left for some graduate student to do a little bit on. The atmosphere here was towards basic physics.

Henriksen:

Do you think universities now look for or keep their eyes out for these things?

Bray:

They’d be more sophisticated about this since so many devices have been spawned by the—. They’ve been sensitized. At least we would be as professors, I don’t know what a fresh student coming in would do. The big problem we had as students was not knowing what aspect of what we were seeing was new and what wasn’t new and what was interesting and what wasn’t interesting. And I can understand that now with some of my own students not knowing what is really interesting, what is significant, what is important and that is after all not only a matter of taste it’s a matter of experience and a matter of knowing what the field is. You begin to recognize when you’ve seen something that is different. So to some extent being naive and innocent was almost easier for us. In those days any day we walked into the lab we could find something new and we didn’t always know what to do with it. If you look at some of my progress reports or those quarterly reports that we sent to the Signal Corps you’ll see that we had discovered all kinds of feedback effects and all kinds of things and we would be shocked when Shockley would publish it a year later, we’d say, "Oh was it that interesting?" And we came out long before him. There was a possibility of a p—n—p—n, four terminal junction. Of course if you put a point contact down near a pn junction you’d have the triode where the soldered contact on the sample is also injecting so that was feeding back things. We were getting current gain and we were discovering the mechanism for current gain and explaining it without realizing that it was a very very important concept. And I can show you that in the old progress reports which probably Bell Labs read and never gave us much credit for. And I remember giving a paper on this fact. Yearian and I got involved in something. He had found that if you put high frequency on a rectifier the resistance would go down and we found out that the reason was that in the forward direction you injected minority carriers. Then in the reverse direction they came back and were detected, so the same point contact you worked as an emitter and...

Henriksen:

A self—transistor.

Bray:

A self—transistor. And in fact I gave a paper and quoted the self— transistor effect and one of the papers of the Chicago meeting of about 1951 or 1950 was on the self—transistor effect. That is the name I gave it and then a year later Bell Labs published it not using that name and Shockley’s name was on it but Shockley had been at the meeting. He was chairing the session where I gave that paper and I never got credit for it.

Henriksen:

Because that was also mentioned in one of the progress reports. And that was before 1949.

Bray:

The self—transistor effect, right. And eventually there was a paper on that by Gossick and myself in Phys Rev. Letters. It was one of the first papers I eventually published, because seeing that Bell Labs was publishing it, we decided we had better write something up. Or someone encouraged me to do it when I mentioned it at one of those meetings.

Henriksen:

So again it was a matter of giving a paper and publishing later.

Bray:

Giving the abstract and then publishing later sometimes much later.

Henriksen:

In your thesis on page 48 it mentions that the Signal Corp's provided you with an oscillator.

Bray:

An oscilloscope.

Henriksen:

Right, How much contact did you have with the Signal Corps?

Bray:

After the war they supported our research for many years. There was the Signal Corps contract that Lark—Horovitz was the head of and Fan after Lark—Horovitz and they kept that up for years and years, They were the main source of money. I guess we got some equipment from them not terribly much, One had to know it existed and being here at Purdue we were sort of isolated. We may not have been aware of equipment that existed. There was a big disadvantage of being here instead of at one of the Eastern schools where there was much more chance to visit around to Bell Labs and GE where some of the other work was going on, so our isolation here was simply a negative factor.

Henriksen:

After the announcement of the transistor, you duplicated the transistor here with p—type germanium?

Bray:

Yes.

Henriksen:

Was that difficult?

Bray:

Actually we realized we were seeing minority carrier injection and all we had to do was inject from the soldered contact, put a reverse contact down and see that we were getting a transference of the signal. We did it immediately with pn junctions also. But again we should have published that. Eventually I guess it showed up in the patent conflicts between Bell Labs and Purdue, Later that day...

Henriksen:

How did the end of the war affect your work on spreading resistance? Did the finishing of the contract change the funding or the emphasis?

Bray:

We got a Signal Corps contract so there was a completely smooth transition and I wasn’t aware of the change particularly. Okay, the big change was that the semiconductor project split up and Walerstein went into teaching and administrative work with respect to teaching and the worst blow was that. I guess, Yearian went back to his X—ray lab which he had come from and Smith who was the only guy I could really talk to was shifted back into nuclear physics because Purdue and Lark—Horovitz started building a linear accelerator and that left on the semiconductor project just a bunch of graduate students including myself. Benzer stayed on long enough to get his Ph.D. and then switched into biophysics. So there was much less intensity and many fewer people to talk to and then around 1948 Bill Fan came and then things perked up again. But there was a gap there where I guess the brightest and most knowledgeable guy was Smith. His shifting out of this was I think a drastic mistake.

Henriksen:

His work on linear accelerators was sort of what he had been working on before the war, nuclear physics?

Bray:

He had been working I guess with the cyclotron and got his PhD in that area.

Henriksen:

So he returned to the work...

Bray:

Well he didn’t go back into nuclear physics so much. He went back into building a machine which would eventually do nuclear physics and where that would end I don’t know because a year or two later he moved out to Boeing.

Henriksen:

I see, so it wasn’t the funding.

Bray:

It wasn’t the funding. It was either the change in interests or being shuffled around by Lark—Horovitz. I don’t know what was his motivation. I stayed with the work because I made the transition from the spreading resistance to the bulk and in investigating the bulk material and the field effects we discovered that there was this high field effect which could modulate the conductivity and then did Hall Effect measurements to show that it was changes in the electron concentration ultimately and then I guess by the time I had worked that out the transistor came out so we began to do transistor type experiments and were doing transient measurements of injection of minority carriers and measurements of lifetime and drift mobility and things like this.

Henriksen:

What was, the reaction here when the transistor was announced? Did it cause great interest, I mean more than it would anywhere else?

Bray:

There was certainly interest. I can’t remember being particularly upset by it. I just don’t remember really too much discussion. People would come around here like I mentioned who had visited here before who said, “Oh when you told us all this why didn’t I realize that.” I guess I was more interested in getting a PhD, rather than thinking about what I was missing in not inventing the transistor. Besides the transistor didn’t seem like all that much. It wasn’t obvious that it would turn into a solid state revolution as it eventually did.

Henriksen:

How did you find out about the carrier injection? Was that from reading the literature or talking to people?

Bray:

Prom reading the papers on transistor action. I guess we were on the verge of it in thinking about such possibilities, but it hadn’t really formulated itself in our minds. That was the one aspect that we missed. But even had we understood the idea of minority carrier injection we might not necessarily have... We would have said, “Oh this explains our effects.” We might not necessarily have gone ahead and said let’s start making transistors, open up a factory and sell them.

Henriksen:

Right.

Bray:

That was the last thing on my mind. At that time the important devices were: the high back voltage rectifier, the diode, the photo conductivities associated with it, maybe even solar cells. There were people working with that and there were also people coming around from Harvard where they were building some of the first computers and wanting to know if these diodes might be usable in their computers for switching.

Henriksen:

The germanium had the higher back voltage than the old silicon diodes. The silicon didn’t have the durability to stand up to the bursts in the back direction.

Bray:

Right.

Henriksen:

Do you remember anything in particular about that visit by Shockley and Morgan right after the war? Or was it just a matter of them coming and you showing them what you were doing?

Bray:

They came here and we showed them what we were doing. I remember also visits by Bardeen and I remember one particular aspect of the interaction because prior to the transistor he had been working on the effects of surface states and this was not an applied problem at all, The point was, what were the surface states and would this produce a different resistivity in the surface than the bulk?

Henriksen:

You and Benzer both had worked on that.

Bray:

We hadn’t worked on it. The possibilities of surface states producing an inversion layer or a layer of different conductivity on the surface than in the bulk was a factor in our discussions of the capacitance. I remember Bardeen discussing the anomalous capacitance in these point contacts and it would have been a factor also possibly in relating to the anomalous spreading resistance except we had already found that it was a field effect.

Henriksen:

Let me ask you again about this Brattain thing just to have that on the tape. This is where he mentions someone, either you or Benzer, asking him about the third electrode. And you said that it was possibly you and that you didn’t remember.

Bray:

Yes, I think the context is that maybe he doesn’t remember completely, the context of the interest in Bell Labs and in what they were doing at the Washington meeting. I do remember talking to him and Becker because I talked to them about the possibility of a job also at Bell Labs after I got my PhD. And there were some tentative... I remember on one of their visits I met with one of them for breakfast here at Purdue, an early breakfast to discuss this and it was Joe Becker and maybe also Brattain, but it was the two papers that we presented, the Hall Effect measurements we were making and the high field effect and I’m pretty sure at that same meeting—maybe you didn’t find it in that bulletin. I am sure there was a paper by Benzer on Hall Effect.

Henriksen:

Now this was at the meeting in Washington in 1949?

Bray:

1949? Now did you look in the index of that meeting?

Henriksen:

Yes I did.

Bray:

And there was nothing there by Benzer?

Henriksen:

Not that I came across. Nothing that I remember. I will take another look and see, I was looking mainly at your name. I might have looked under Benzer, but I’m not sure.

Bray:

Maybe he had a Phys Rev Letter someplace, I certainly remember that. And that certainly involves a third electrode. The combination of the Hall effect that we reported and the fact that he was doing Hall effect on the surface would certainly have been a big warning blow to the Bell Lab people that we might stumble across this thing at any time. By the way their own initial explanation of what they were doing was wrong too. They visualized it as a surface effect because they were locked in initially to the surface mechanism if you read the original paper by Bardeen and Brattain. They did not visualize it as a bulk minority carrier injection. [Shows him copy of the original transistor paper in Phys. Rev.]. They talk about the mutual influence which makes it possible to use the device to amplify AC signals, and I think they talk about it. I haven’t read this paper in years and years. Maybe if I read it again now I would change my mind, but it seemed to relate to a surface current, maybe not. It says there is a small forward bias in the emitter which causes a current of a few milliamps to flow into the surface. It is not very clear just how the interaction takes place or the nature of the forward current, but that is the second paper. Well it certainly became clear subsequently. It wasn’t all that clear in the first papers just how to visualize it. The way that it affected me mainly was that I had to incorporate all this new knowledge into the understanding of all the work I had done for my thesis and to see whether—analyze the various results I got. So I guess that was the main effect. It stimulated me to take their mechanism of minority carrier injection to explain everything that we had seen.

Henriksen:

Now had you been close to finishing up your degree before this or did this come in the middle? You got your degree in 1949?

Bray:

Yes, I was told to go ahead and write my thesis about two years—. When was this announced? At the Washington meeting in 1948?

Henriksen:

This one says June 25, If that was the first paper,

Bray:

All I remember was that Lark-Horovitz asked me about my thesis, I said I hadn’t written it yet. And he says you haven’t? And I remember with all these new things coming out I was really assessing everything I had done and trying to interpret it and I spent quite a long time on it as well as doing some other experiments and that was all my fault, I probably could have finished it two years earlier, When did I finish it in 1949?

Henriksen:

I think it was 1949.

Bray:

It was surely 1949. Yes I remember what happened. I was also in the process of—, I had met the woman who was going to be my wife and I spent at least as much time writing letters to her as I did writing my thesis and so I didn’t finish it until after I got married.

Henriksen:

I’m not sure if there is much more to say about this or not but there is that abstract that I showed you from one of the crystal meetings during the War. Was there much of a reaction to your discussion of spreading resistance? Either that one or the next one, whichever of those meetings you were at, I think it might have been the October meeting.

Bray:

Was there much reaction? Were there any questions in the audience? Because if I remember correctly at that meeting at Columbia I was the last speaker and I was told to finish up in five minutes and then we all left, so there wasn’t much time for questions. I don’t think I remember if there was a big reaction or not.

Henriksen:

That was probably earlier.

Bray:

It was one of these full day meetings.

Henriksen:

Have we left anything out?

Bray:

I guess the main point I want to make is that it was in some ways a very exciting period because you could go into the lab every morning and find a new effect every other day and then you’d wonder which one you should pursue. It was hard to get a perspective. There were other areas of research pursuit that didn’t even appear in my thesis. You could easily go in and find something and spend a month or two pursuing it and wonder what to do with it and then go off into something else. There was the fact that we had these weekly meetings and Lark-Horovitz practically demanded that you find something every week, but he didn’t really provide the direction, tell you what to pursue and what not to pursue. It would have made a tremendous difference if there was someone with real insight and leadership to know what was important and what wasn’t. That doesn’t mean they would have been right, but they might have followed up something’s and finished them off.

Henriksen:

Would have had a better chance of putting some of the things together.

Bray:

Yes.

Henriksen:

Seems like you had a lot of the experimental points there.

Bray:

We had all kinds of phenomena. We could have knocked off one after another, published them and gone on to something else in a more systematic way, but what was completely missing was the systematic approach to it.

Henriksen:

Did you ever think about leaving Purdue after you got your degree?

Bray:

I certainly did before I got married, This was a terrible place to be for a bachelor. Then my wife came here and she was finishing up her bachelor’s degree here.

Henriksen:

Was she in physics also?

Bray:

No, she majored in psychology. I probably would have gone and taken that job at Bell Labs. I certainly wouldn’t have stayed here, but then I stayed on until she got her degree and by that time I also got a fellowship to go to Europe for a year. It was from the National Advisory Council on Aeronautics. It was one of the first few fellowships after the war. That came in 1951, just about the time I finished my degree and she finished her bachelor’s degree and I was in Holland at Delft for a year and then spent three months at Reading in England where they were working on semiconductor work, and then came back to Purdue and just about that time got my assistant professorship. And it was just very convenient to stay on here. I got involved in new types of measurements, lifetime measurements, There was never any pressure on me to do anything except what I wanted to do. It was always a question of doing whatever I wanted. With that aspect of complete freedom in a sense there was both a lack of pressure and complete freedom and there was never any incentive, real incentive, to go out into industry which was an unknown. I had no idea what it would be like.

Henriksen:

Did Lark-Horovitz’s attitude about research change much after the war?

Bray:

There was never any big push for publications, so I probably lost a dozen publications because of this and that work never really got written up, but he did initiate a lot of new research directions, the infrared research which he did with professors Meissner and Fan and he initiated the radiation damage work which became a very big undertaking and the linear accelerator which was eventually built, but was never used for nuclear physics essentially, it was used for radiation damage, by MacKay. You have interviewed MacKay?

Henriksen:

I haven’t talked to him yet. I had originally planned to look at Purdue in the 50s also, but they changed my project. They want me to stop at the end of the war and do the whole MIT Rad Lab, So I am going to draw up a kind of a guideline for people to use later,

Bray:

Okay, well the transition is interesting. Lark-Horovitz was a man of many enthusiasms, He could get very excited about things. He’d come back from meetings with things he had heard and start whole new lines of research, but as I said he got very very much involved with the radiation damage work, He got very involved with the infrared work, He got very involved with the work done on Hall Effect and resistivity done at very low temperatures. He started a low temperature lab, but nearly always left me alone, because somehow my work and my observations did not fit into his preconceptions or into his knowledge, so I was left alone.

Henriksen:

With good and bad results.

Bray:

Right.

Henriksen:

An interesting man.

Bray:

Right, he is a fascinating individual. One thing that one should mention is the one thing one learned from him was the enthusiasm for research. The enthusiasm for finding things. What one did not learn from him was how to pursue something systematically and write it up. But he certainly provided an air of excitement and great enthusiasm. A lot of the people here provided more of a systematic approach and at the same time might even quench your enthusiasm by being too critical, but this is just the different ways in which individual personalities enter into it. I think that is just about it.

Henriksen:

Takes care of my questions too. Thank you very much.

Bray:

You are very welcome.