Interface-alloy epitaxial heterojunctions

Abstract

Abrupt epitaxial heterojunctions have been produced by melting the lower-melting-point semiconductor at the interface between two different semiconductors. When the temperature is reduced the melted semiconductor recrystallises, having alloyed into the higher-melting-point semiconductor. Heterojunctions between GaAs and Ge and between GaAs and GaSb have been produced. Kossel line techniques have been used to prove conclusively that the GaAs-Ge heterojunction is single crystal. Similar but less definitive results for the GaAs-GaSb couple indicate that this heterojunction is also single crystal. In the interface alloying the wafers rotate and/or tilt with respect to each other as required for single crystal regrowth, which appears to be the lowest energy method for regrowing. Electron beam microprobing shows that for the GaAs-Ge couple the transition from GaAs to Ge in the alloyed region is not monotonic, while for the GaAs-GaSb couple the transition from As to Sb is abrupt and without structure. As expected from the known electrical activity of Ge in GaAs and Ga and As in Ge the electrical characteristics of the GaAs-Ge heterojunction cannot be explained by simple heterojunction theory. A possible explanation in terms of tunneling through the barrier at the crystal interface is offered for the forward current of the GaAs-GaSb heterojunction which varies as I 0 exp( AV).