Determination of the valence-band discontinuity between GaAs and (Al,Ga)As by the use of p+-GaAs-(Al,Ga)As-p−-GaAs capacitors

The valence-band discontinuity between GaAs and AlxGa1−xAs (0.3≪x≪1.0) was determined from measurements on p+-GaAs-(Al,Ga)As-p−-GaAs capacitors from current-voltage measurements as a function of temperature. It was found that thermionic emission dominated the conduction process in these structures for temperatures above 140 K and for low bias voltages. The barrier height was determined from the slope of ln(J/T2) vs l/T. From this, a valence-band discontinuity of 35% of the total direct band-gap (EgΓ) discontinuity, being independent of the mole fraction x, between GaAs and (Al,Ga)As was calculated. The corresponding value for the conduction-band discontinuity, 65%, is considerably lower than the commonly accepted value of 85%.