Effect of Crystal Orientation on Ge-GaAs Heterojunctions

The electrical characteristics of Ge-GaAs heterojunctions, in particular n-n junctions, have been studied experimentally. Barrier voltages, determined from the temperature dependence of reverse current and from capacitance vs voltage, depend upon the crystal orientation of the interface. This is seen to imply a corresponding variation of the conduction band discontinuities; namely ΔEc[111]Ga > ΔEc[111]As >ΔEc[110]. The voltage dependence of the reverse current is interpreted in terms of the shift of the Fermi level with respect to the conduction band edge in the accumulation layer. The transient behavior of n-n heterojunctions yields a switching time for 20 mA less than 10−9 sec, and no observed storage time.