Current-voltage characteristics ofp-Ge/n-GaAs heterojunction diodes grown by molecular beam epitaxy

Electrical characteristics ofp-Ge/n-GaAs heterojunctions on GaAs(l00) grown by molecular beam epitaxy (MBE) have been investigated. Thep-type Ge layer was produced by intentionally doping with Ga atoms, in addition to the diffusion of Ga atoms from the surface of the GaAs layer. The best ideality factor of 1.04 over six decades of the forward current and the lowest reverse current density of the order of 10⁻⁶ A/cm² were obtained for diodes with Ge grown at 500° C. The ideality factor increased slightly up to 1.12 when the operating temperature was decreased to 77 K. By studying the temperature dependence of the forward current, the conduction band discontinuity has been estimated to be 40 ± 10 meV. The suppression of Ga diffusion into the Ge film and its effect on pn-junction characteristics were also studied by growing a thin Ge film on GaAs at less than 300° C prior to the normal Ge film growth at 500° C.