Degradation of AlGaAs/GaAs HBTs induced by hot carriers

In AlGaAs/GaAs HBTs, the instability of the surface states of the extrinsic base, which is revealed by mesa-etching and passivated by Si₃N₄, affects reliability. In this study the reverse constant current stress in an avalanche regime is applied across the emitter–base junction in order to test the stability of the heterojunction and the surface state of the extrinsic base. It has been identified that the surface of the extrinsic base is vulnerable to hot carriers. A new degradation mechanism is suggested and verified by numerical simulation. In addition, a way to improve the reliability is proposed based on the experimental results.