SILICON-CARBIDE MICROWAVE FIELD-EFFECT TRANSISTORS - CUTOFF FREQUENCY AND POWER

An analysis is made of the cutoff frequency and the corresponding microwave power of field-effect transistors (with a p-n gate or a Schottky gate) on the basis of a well-known model which allows for saturation of the drift velocity of electrons in strong electric fields. Calculations are reported of possible values of the cutoff frequency and power of field-effect transistors made of the 6H polytype of silicon carbide, which is a semiconductor characterized by an avalanche breakdown field (approximately 5 X 10(6) V/cm) an order of magnitude higher and a saturation velocity of electron drift (2 X 10(7) cm/s) a factor of 2 higher than the corresponding parameters of silicon and of gallium arsenide. A comparison is made of the power-cutoff frequency characteristics of SiC(6H) and GaAs transistors with a gate length 1.5-0.3-mu-m. It is shown that SiC(6H) transistors can operate in the frequency range 10-100 GHz with an output power 100-7 W, whereas in the case of GaAs transistors the frequency range is 10-50 GHz and the corresponding output power is 4-2 W. The results thus demonstrate that SiC(6H) can realistically be a material for high-power (with outputs of tens of watts) transistors operating in the millimeter microwave range, even assuming no further progress in lithographic techniques.