Influence of buffer layer thickness on DC performance of GaAs/AlGaAs heterojunction bipolar transistors grown on silicon substrates

The DC performance of GaAs/AlAs heterojunction bipolar transistors (HBTs) grown on silicon substrates with buffer layers ranging from 0 to 5 mu m was investigated. Current gain, collector-emitter breakdown voltage, emitter-base and collector-base diode ideality factors, and breakdown voltages were measured as the buffer layer thickness was varied between 0 and 5 mu m. The current gain steadily increases with increasing buffer layer thickness until the layer reaches 3 mu m. However, the other DC parameters are relatively insensitive to the buffer layer thickness. A small-signal current gain of 60 is typically achieved for devices with 6*6- mu m/sup 2/ emitters at a density of 6*10/sup 4/ A/cm/sup 2/ when the buffer layer is >or=3 mu m.<>