The first general-purpose microprocessor, the Intel 8080, released in 1974, could execute about half a million instructions per second. At the time, that seemed pretty zippy.
Today the 8080's most advanced descendant operates 100 000 times as fast. This phenomenal progress is a direct result of the semiconductor industry's ability to reduce the size of a microprocessor's fundamental building blocks--its many metal-oxide-semiconductor field-effect transistors (MOSFETs), which act as tiny switches. Through the magic of photolithography, billions of them are routinely constructed en masse on the surface of a silicon wafer.
As these transistors got smaller over the years, more could fit on a chip without raising its overall cost. They also gained the ability to turn on and off at increasingly rapid rates, allowing microprocessors to hum along at ever-higher speeds.
But shrinking MOSFETs much beyond their current size--a few tens of nanometers--will be a herculean challenge. Indeed, at some point in the next several years, it may become impossible to make them more minuscule, for reasons of fundamental physics rather than nuts-and-bolts engineering. So people like me have been looking at other ways to boost their speed. In particular, we've been laboring to build them using compound semiconductors like gallium arsenide, which would allow such transistors to switch on and off much faster than their silicon cousins can.
This strategy is by no means new. Practically ever since the silicon MOSFET was invented in 1960, engineers have been attempting to come up with a gallium arsenide version suitable for large-scale integrated circuits. No one has yet succeeded. Those repeated failures have led to the oldest joke in Silicon Valley: gallium arsenide--it's the technology of the future, and it always will be.
But that perennial skepticism may be about to vanish. My colleagues and I at Purdue University's Birck Nanotechnology Center, in West Lafayette, Ind., along with other researchers in industry and academia, have recently made some advances that might soon allow transistors built with gallium arsenide or a related compound to be used for large-scale digital ICs. That capability would go a long way toward bringing us microprocessors that can blaze along at triple or even quadruple the speed of today's best. Achieving that goal will no doubt require other improvements in semiconductor technology to take place in parallel, but gallium arsenide or something close to it could be key. No wonder some of us have been unwilling to give up on this remarkable material.
Gallium arsenide's two main components come from the third (gallium) and fifth (arsenic) columns in the right-hand portion of the periodic table of elements, which is why cognoscenti refer to it as a III-V semiconductor. There are more than a dozen such compounds, including gallium nitride and indium phosphide, but gallium arsenide is the most common example and therefore the best studied. It currently accounts for about 2 percent of the semiconductor market.
Gallium arsenide devices cost a lot more than ones built of silicon--the raw materials are about 10 times as expensive--but they serve well for certain specialized applications, including high-efficiency solar cells, laser diodes, and one very special kind of field-effect transistor: the high-electron-mobility transistor, or HEMT, which is used in cellphones, communication systems, and radars, among other things.