n- AlGaAs /p- GaAs /n -GaN heterojunction bipolar transistor wafer-fused at 550–750 °C

We recently reported an initial AlGaAs/GaAs/GaN heterojunction bipolar transistor (HBT), formed via wafer fusion of a p-GaAs base to an n-GaN collector. The device was formed by fusion at a high temperature (750 °C) and demonstrated low output current (∼100 A/cm2) and low common-emitter current gain (0.5). This letter describes a systematic variation of fusion temperature (550–750 °C) in the formation of the HBT, and reveals the correlation between fusion temperature, base–collector leakage, and emitter–base degradation. With reduced fusion temperatures, devices demonstrate improvements in leakage, output current (∼1 kA/cm2), and common-emitter current gain (>1). Optimization of device structure should further improve performance.