On the investigation of degradation mechanisms in ultrahigh performance GaAs heterojunction bipolar transistors

Summary form only given. Recently, current-induced degradation in the form of V_BE shifts has been reported when the heterojunction is stressed under high-level forward current injection. Although the V_BE shift is an indication of device parameter change, the degradation mechanisms cannot be readily identified. An approach is presented that uncovers the device degradation mechanisms by measuring the inverted mode I_C at room temperature and the forward mode I_B at low temperature. The correlation between the change in the inverted I_C and an anomalous component (tunneling current) of I_B is observed and attributed to beryllium interstitial diffusion into substitutional sites