Current gain deterioration in carbon-doped AlGaAs/GaAs heterojunction bipolar transistors during high-temperature bias stress tests

Abstract

We investigated the current gain deterioration in carbon-doped AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Bias stress tests showed that mechanical stress can accelerate the gain reduction, since HBTs with a thicker SiN passivation layer have a shorter device life. The longest life was obtained for base layers closely lattice matched to the GaAs substrate using In doping. The gains of such devices were stable for more than 10 4 h at a junction temperature of 250°C. By analysing the base current increase, we found two kinds of degradaon mode. Base current ideality factors are much greater than two for shorter life devices and are nearly two for longer life devices.