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Interview of H. Y. Fan by Lillian Hoddeson on 1977 April 22,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Recollection of the work done on semiconductors at Purdue University after World War II. Major topics include Fan's education at Massachusetts Institute of Technology, his recollections of the Purdue physics department in the 1940s, and work on semiconductors at Purdue in the 1940s. Also prominently mentioned are: Ralph Bray, Karl Lark-Horovitz, A. H. Wilson; Lawrence Radiation Laboratory, and Massachusetts Institute of Technology Radiation Laboratory.
This is Lillian Hoddeson and I'm interviewing Professor Fan at Purdue late on a Friday afternoon at 5:20 and we plan to talk a little about semiconductor research in the late 40's at Purdue.
Well, as I understand it, semiconductor research at Purdue started in about 1942, mainly on germanium in the 40's. The motivation was the technology of microwave detectors. At about the same time, the exploration of silicon microwave detectors was carried out in the University of Pennsylvania and Bell Telephone Laboratories, I think.
Yes, that's right. Yes, the people at the Holmdel laboratories surrounding Russell Ohl and others, such as Southworth, were exploring silicon, along with lots of other materials.
As you will see in these volumes of reports that the effort in the exploration of germanium for use as microwave detectors was conducted together with study of semiconductor physics — Germanium, silicon and tellurium. In that respect, semiconductor physics — Hall Effect, resistivity, thermo-electric power were studied for several semiconducting materials such as germanium, silicon, and tellurium as I just mentioned.
I want to ask a question. The group was led by Lark-Horovitz and the work was really going on, I gather at four places at once: Purdue, Penn, MIT "Rad-Lab" and Bell. I was wondering whether you knew how close the interactions were — whether these labs were, in some sense, competing, even though they were working on the common War effort.
As I remember it, there were meetings of these groups you just mentioned from time to time. I mean by that, once a year maybe; maybe even more than once a year.
Did they view their work as part of a joint effort, these four? Or were they competing in some sense because they were all doing it for war purposes at that time.
Yes, I do not think they were competing in the sense like privileged information in research laboratories of different companies. They were not cooperating in the sense that they had one problem where one group studied one aspect and asked the other group to study another aspect as if the other group was in the same group. Now as far as the device is concerned, the rectifier, the point contact rectifier, was one part, perhaps the part that motivated the semiconductor physics research in the first place. You will see in these volumes of reports every volume contains a part on rectifiers, on junctions. Well, as to the contribution to semiconductor physics that you can see in the reports, Hall Effect, resistivity, electrical transport properties at room temperature and down to lower temperatures. The lower temperature did not reach liquid helium temperature until about 47-48, at which time Purdue purchased a liquid helium cryostat, and was one of the first research laboratories which studied semiconductor physics down to liquid helium temperatures. As to the devices, rectifiers, the contribution is the characteristics of rectifiers, forward-backward, current voltage characteristics and, notably, so-called "high-back voltage rectifiers," and photo-diodes. And in connection with that, in about 1947, the phenomenon was found that the so-called “spreading resistance" of the rectifier when it is biased in the forward direction was not a constant. Rather it decreased with increasing bias voltage. This was the work of several people, including Bray. That was not grasped in its significant physics as injection of carriers from contact — holes injected from the point contact into the n-type germanium crystals.
It was not recognized by Bray and his co-workers. I see.
And that, in my view, is the basic physics of transistor physics for which three people received a Nobel Prize; Bardeen, Brattain and Shockley.
So Bray and his colleagues went up to the line but they were not able to…
They saw the phenomenon but did not realize the significance of the phenomenon.
I see. I notice in one of these reports — there's a summary on November 1, 1948, it’s called transistors, and it's by Bray —
The word "transistor" is mentioned; that obviously is written after the publication in Physical Review Letters by…
Bardeen and Brattain. Yes.
Please look into the earlier reports, before the one you mention about spreading resistance.
So that's the significant phrase, for me to trace down.
I think this brings my three minutes guideline to the end, for whatever it's worth.
I appreciate it, thank you very much.
Perhaps, I would think, from the physics point of view, the contribution of the Purdue group is mainly the fundamental studies of semiconductor properties, secondly, the purification of germanium and doping with various kinds of impurities. Nowadays, we do it with great skill, preparation of crystals, pure and doped with the impurities specified. This is also because, with regard to the preparation of semiconducting crystals, chemistry and metallurgy as well as crystallography are involved. The Purdue group has the benefit of Lark-Horovitz who was a physical chemist to begin with. He was a physical chemist with experience in X-ray crystallography when he was in Austria.
Did he get personally involved in the experiments? He was directing so many people.
I would say he was very much involved. He was not only directing the semiconductor physics research, but he also was the head of the department. There were many administrative chores.
One wonders how he actually found the time to go into the labs himself, with all the many things he was doing at that time…
Yes, he did. He visited laboratories and talked to and watched people doing experiments, and discussed with people doing theoretical work. He made a round of the physics building almost every day after 8 or 9 o'clock in the evening, and went home one or two or three o'clock in the morning. He did not come into the physics building until 10 or 11 o'clock in the morning.
So that's how he worked then.
Yes. He was deeply involved in the scientific research. I can attest to that by my own experience. I went in to talk to him or he came by into my office or laboratory to see what I was doing. When I went to his room to tell him what I was doing, what results I had to discuss, and the scientific interest of my activities, he would frown at me as I came in as if he was very upset by the intrusion. But when I told him what I came to see him for — scientific research results — he would immediately show great interest. The frown disappeared, replaced by concentrate and stimulated discussion.
Did he hire you in '48?
You were at MIT at that time.
No, I was going home to China.
But you had just been in China and you had come back for a year.
I went back to China after I got my Ph.D. degree at MIT in 1937.
Yes, and you stayed in China for 10 years.
I stayed 10 years, then I came back for one sabbatical year to MIT, and I was leaving the United States to go back to China when Professor Lark-Horovitz invited me to come to Purdue for one or two years.
And so you came for a year or two and then you stayed.
Yes. I came and I stayed.
Was that the first time you had met Lark-Horovitz when you came up — there to MIT?
I first met him in 1948, in the early part of 1948 at MIT. He went there to visit a scientific collaborator at MIT, Professor Nottingham. And I met him there. He made the offer, "Come to Purdue for one year or two years as you like." So I did.
And then I gather you were very happy here in the Purdue environment.
I was very happy here. And also in those years, there was turbulence in China and I could not for other reasons go back to China.
So you might have stayed even had Lark-Horovitz not come up to MIT and given you the offer.
No. I had already bought tickets to go back.
Oh, I see. The turbulence began after you came to Purdue. And then you were very happy that you had stayed here in fact.
I hope you are not taking this down — this is irrelevant to your interest in Purdue's scientific research activity.
It is relevant in an important sense: when we try to put history together we must know a little bit about the background of the individuals who were part of the history or who report on the events. Otherwise history reduces to names and lists of papers and titles and it's very dried out. The people make the story, after all. Quite often — when one goes to an archive to learn about events there's a file on the individuals — there's usually something about their background, where they went to school, about their family life in some cases, and so on. So our discussions about your education are by no means irrelevant.
I understand. About this Purdue scientific research in, shall we say semiconductor physics, another point I might mention to you: in 1948 Professor Lark-Horovitz started studying radiation damage in semiconductors — high energy particles bombarding semiconductors creates structural defects and transmutation of some atoms. The study of radiation effects on semiconducting materials was pioneered by Lark-Horovitz.
I didn't realize that.
You can see that in the 1948 report.
I shall look. By the way, one other question: when you were at MIT as a student, did you interact much with Slater, who was there then?
Yes, he was my professor. I took courses with him.
I see. Was he a strong influence on you at that time?
I only took two courses with him.
What did you actually take your degree in?
I got my degree in the Electrical Engineering Department. My thesis supervisors were one professor of electrical engineering, and one professor of physics.
And who were they?
The professor in electrical engineering who was my thesis supervisor was Professor Ralph Bennett, and the professor who was in the Physics department, my thesis supervisor, was Professor Nottingham. Then, before I finished my Ph.D. research a third thesis supervisor was added to the two supervisors. That was about a year, perhaps a year and a half, before I finished. This professor was a scientist from Germany who left Germany to come to United States. This professor's name is von Hippel. I would say that probably the three all had influence in my scientific career. Perhaps the strongest influence was that of Professor von Hippel.
What was his specialty in that period?
His specialty: dielectrics, and imperfections in dielectrics.
There was then a rather substantial effort in the early 30's at MIT in —
— not on semiconductors.
— but on solids in general.
Solids, yes, quite so. But semiconductor research in the United States really started strong activity only in 1942, 41.
I see. Well, I haven't looked at this yet very carefully or very deeply, but at Bell Labs there were people like Brattain, who worked with Joe Becker, and who were looking at copper oxide rectifiers.
That was a very small beginning, a very small effort.
I gather they really didn't understand what they were doing very deeply.
You would not have considered that the beginning of semiconductor research in the 50's, 60's, 70's. To be sure, semiconductor physics began with Wilson's theory of semiconductor energy bands. That was even earlier, in the 30's.
I can check that date right here (pulls out a paper). Here, yes, 1931 Wilson's quantum mechanical model of a semiconductor — yes "The Theory of Electronic Semiconductors."
That's quite right. That is the concept that a semiconductor has an energy gap.
But, I gather that it took some ten years before materials were pure enough to study this concept experimentally.
It took ten years before semiconductors received large attention from many, many scientists. This (indicating the Wilson 1931 paper) was the seed. It was like an iceberg's tip: you see a tip of ice, how much is there under water intrigues you. In another figure of speech the more you dig, the more wealth you find, so you dig more and more. The mushrooming of semiconductor physics research was motivated, I think, by the technological need during the war — microwave radar needs a detector that's small in size and works for microwave. That's what made the start. The Federal Government wanted several groups to study it, the University of Pennsylvania, Purdue, Bell Laboratories, and MIT Rad-Lab.
You didn't work with the MIT Rad-Lab, did you?
I did. No, not the Rad-Lab, the so-called Radiation Laboratory at MIT; after the war it became the Research Laboratory of Electronics. That was the continuation.
I see, I see. Okay.
When I reached MIT for sabbatical in '47, it was no longer Radiation Laboratory, but it was in the same building. Not the same staff, by the way: the Radiation Laboratory had scientists from all over the United States —
— during the War and then they went home.
— then they went home. If you want to read about rectifier work at the Radiation Laboratory you can read a book
Torrey and Whitmer?
I've seen their book, a very fine report.
You will see, they had information from various groups and the information they obtained from Purdue is written there.
I must go back and read that carefully. Well, I'm very pleased that you were able to give me some time this afternoon.
After reading these reports and books, you can scrap the tape for misleading information. I might have misled you by this few minutes brief, personal view.
Maybe I will, maybe I won't. I believe we've covered some interesting ground. I certainly won't show it to anybody without your permission.
Oh, it doesn't matter even if you show it to anybody; it doesn't matter to me. But I would like to see what did I say?
In that case, I will get this short interview transcribed and send you a copy.
Whenever you have the time to do it. I appreciate it.
I thank you very much.
 Progress reports of the Lark-Horovitz group 1945-8 available in Physics Department, Purdue