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 th e exposed junction surfaces in InP/InGaAs heterojunction bipolar trans istors have been studied and shown to degrade the transistor propertie s. These effects are ascribed primarily to surface damage associated w ith the high SiN deposition temperature (350-degrees-C). A degradation of the emitter-base properties was observed through the nonideal beha vior of the base current and the measured short minority-carrier lifet ime in the base, extracted by using the base width modulation method. Degradation in the current gain and emitter injection efficiency was a lso observed. A clear recovery of the transistor was observed after re moving the SiN passivation layer indicating that the high SiN depositi on temperature results in a high-surface-state density which increases the surface recombination velocity and degrades the junction properti es. It is concluded that a low-temperature deposition and good quality dielectric are necessary to exploit the excellent electrical properti es of InP-based heterojunction bipolar transistors.