A Quantum Leap to Smaller Chips

It is commendable to assume that today’s desktop computers have become more powerful in comparison to machines that occupied the whole room a few years ago only. This fast scaling of this feature is an extraordinary example of how successful electronics have been working based on semiconductors. A modern car engine is likely to be controlled by a computer containing a microprocessor, as are the latest passenger aircraft-so called fly-by-wire systems.

These include aluminum and indium in group III and phosphorous in group V. These so called III-V materials have tremendous potential. They work at the fast speeds needed for the most powerful supercomputers. Gallium arsenide also operates at higher frequencies than silicon, providing communications systems that can carry more information and exploit previously inaccessible regions of the electromagnetic spectrum.

Another important niche for gallium arsenide is in optoelectronics, the interface between optics and electronics. Unlike silicon, gallium arsenide can both detect and generate light. Also, some optical computers rely on devices made of gallium arsenide.

The most exciting use of gallium arsenide and related materials, however, is in creating minute electronic structure that exploits the wave-like nature of electrons predicted by quantum mechanics. This contrasts with conventional devices, which can largely be understood with classical mechanics. Novel devices based on quantum mechanics should not only lead to smaller and faster computers and communications systems that consume less power, but they are already helping physicists to understand the subtle behavior of electrons at the quantum level.

All electronic devices depend on electrons moving about in some controlled way, so that there is either an electrical current or no current across the active region of the device. In a computer, this on-off switching provides the means of passing and processing information in binary code consisting of 1s and 0s. How fast a device can respond depends on the time taken for the electrons to cross the active region. There are two ways to reduce the time-by making the electrons move faster or the device smaller.

In integrated circuits, the minimum size of the device is dictated by how easy it is to fabricate. One can now make silicon chips with features smaller than a micrometer. But there may be a minimum size below which conventional silicon devices will not work. New kinds of devices or materials are needed to break the limit. Gallium arsenide and other III-V compounds may provide both.

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