Electrical characterization of GaAs/AlGaAs semiconductor-insulator-semiconductor capacitors and application to the measurement of the GaAs/AlGaAs band-gap discontinuity

Abstract

Electrical measurements were made on n+GaAs-(Al,Ga)As-n−GaAs and p+GaAs-(Al,Ga)As-p−GaAs capacitors. Current conduction is due to thermionic emission at low bias voltages and high temperatures. At low temperatures and high fields Fowler-Nordheim tunneling contributes to the conduction process. An inverted n-type capacitor analogous to an inverted modulation doped structure shows electrical characteristics comparable to the ‘‘normal’’ structure grown under optimized conditions. Conduction- and valence-band discontinuities were calculated from measurements of thermionic emission barrier heights as a function of Al mole fraction in the (Al,Ga)As. A conduction-band discontinuity of 65% of the total band-gap discontinuity between GaAs and (Al,Ga)As, independent of Al mole fraction, was deduced. A classical theory for the capacitance voltage characteristics of p+GaAs-(Al,Ga)As-p−GaAs structures is presented.