Number 298 (Story #3), December 4, 1996 by Phillip F. Schewe and Ben Stein AN ALL-SILICON OPTOELECTRONIC CIRCUIT has been developed at Rochester University. Silicon is of course the backbone of the ubiquitous microelectronic culture. (Quoted in the 28 November issue of Nature, Gordon Moore of Intel ventures to estimate that every year more transistors are made than the number of raindrops falling on California.) Silicon, unfortunately, emits light only grudgingly, a decided obstacle to integrated electronic-photonic circuitry. However, a few years ago physicists found that silicon can generate light if it is etched with acid into a tangle of micro-filaments. Problems in using this porous silicon as a light source include poor efficiency, slow speeds, and chemical instability. As these shortcomings have been addressed in the past year, it has become possible, as the new Rochester device demonstrates, to incorporate films of the porous silicon into a conventional integrated circuit. Speed, power considerations, and efficiency have to improve further, the researchers concede, if the circuits are used in practical LEDs. (Hutchings et al., Nature, 28 November 1996.)