Gallium arsenide (device applications)

The device potential of GaAs and the problems inhibiting its widespread use are examined. Problems encountered in growing wafers are stringent process requirements for obtaining pure material, high susceptibility to lattice defects, small size (2-3 in) of wafers that can be grown, low thermal conductivity necessitating a special heat sink, and the uselessness of native oxide, which must be avoided during manufacture. With respect to the microelectronic properties, the speed of GaAs devices is much higher, with electron velocities measured up to five times that of comparable silicon devices. With very high transconductances and low input capacitances, GaAs devices can obtain much higher gain-bandwidth products (up to 15-20 GHz) that lead to switching speeds of up to 50 ps, about half the speed of silicon. However, this speed advantage erodes at high levels of integration, where costs demand simple and compact packaging. The reasons whey technologies available today for silicon devices-the bipolar junction transistors (BJTs) and field effect transistors (FETs), specifically the MOSFETs-do not work well for GaAs are examined, and new device technologies for GaAs devices-the metal-semiconductor field-effect transistor (MESFET) and the heterojunction bipolar transistor (HBT)-are described.<
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