Temperature dependence of Al/undoped Al(0.5)Ga(0.5)As/GaAs capacitors

Undoped Al(0.5)Ga(0.5)As is used in place of the insulator layer in the fabrication of MIS-type capacitors with Schottky gates. The current-voltage and capacitance-voltage characteristics of the capacitors were measured as a function of temperature in the range 300-77 K. At high temperatures, current is by thermionic emission over the barrier determined by the Schottky contact and the Al(0.5)Ga(0.5)As/GaAs conduction band discontinuity. As the temperature is lowered, Fowler-Nordheim tunneling is observed at sufficiently large gate biases, and at 77 K conduction is ohmic. Based on I-V and C-V data, the electron accumulation layer density is estimated to be about 1 x 10 to the 12th/sq cm at 77 K when the capacitor is positively biased. The results obtained indicate that for an appropriate choice of parameters it should be possible to fabricate MIS-like transistors suitable for high-speed operation at 77 K.