Effect of surface passivation with SiN on the electrical properties of InP/InGaAs heterojunction bipolar transistors

The effects of the SiN layer normally used to passivate and protect the exposed junction surfaces in InP/InGaAs heterojunction bipolar transistors have been studied and shown to degrade the transistor properties. These effects are ascribed primarily to surface damage associated with the high SiN deposition temperature (350 °C). A degradation of the emitter‐base properties was observed through the nonideal behavior of the base current and the measured short minority‐carrier lifetime in the base, extracted by using the base width modulation method. Degradation in the current gain and emitter injection efficiency was also observed. A clear recovery of the transistor was observed after removing the SiN passivation layer indicating that the high SiN deposition temperature results in a high‐surface‐state density which increases the surface recombination velocity and degrades the junction properties. It is concluded that a low‐temperature deposition and good quality dielectric are necessary to exploit the excell...