The characteristics of GaAs are such that it performs well as a solar cell and light emitter, and its energy band structure makes possible transferred electron (Gunn) oscillations. Because of its high electron mobility and saturation drift velocity, this material offers distinct advantages in the field of high frequency operation. In the intrinsic state, it has a high resistivity at normal temperatures and therefore components made on an intrinsic substrate may not need an isolation diffusion. Also, owing to its greater energy bond gap than silicon, operation at higher temperatures is theoretically possible. Unfortunately, this material is difficult to process and therefore production costs are much higher than in the case of silicon, and this fact has certainly inhibited its much wider use in the past. One problem is that it does not grow an electrically stable oxide layer in the same way as silicon, since one element oxidises more rapidly than the other, leaving a metallic phase at the interface, thus rendering planar processing impossible. Since arsenic evaporates from the melt and the crystal above about 600°C, diffusion techniques cannot be used. Furthermore, gallium arsenide is difficult to dope and crystal defects tend to be higher than is the case for silicon. Consequently, techniques for fabricating devices from this material have taken much longer to develop than was the case for both silicon and germanium.

Inspec keywords: III-V semiconductors; solar cells; gallium arsenide; crystal defects; Gunn oscillators; high electron mobility transistors

Other keywords: high electron mobility; metallic phase; Gunn oscillation; transferred electron oscillation; GaAs; diffusion techniques; crystal defects; light emitter; gallium arsenide; planar processing; energy bond structure; solar cell

Subjects: Oscillators