A p n p AlGaAs/GaAs heterojunction bipolar transistor

Preliminary results of the first successful operation of pnp AlGaAs/GaAs heterojunction bipolar transistors grown by molecular beam epitaxy are reported. A common emitter current gain of 50 was obtained for a base width of 0.1 μm. For collector currents larger than a certain value, a negative output differential resistance (NDR) was seen at temperatures between 360 and 83 K. The onset of collector current for NDR was found to increase with decreasing temperature from 40 mA at 360 K to 200 mA at 83 K for emitter-base junction area of 10 μm×50 μm. The NDR was seen for both common base and common emitter characteristics and for both constant input currents and voltages. Increased surface recombination current at the edges of the emitter-base junction at large electric fields, large currents, and high temperatures appears to be the cause for NDR.