Degradation properties of MOVPE-grown GaInP/GaAs HBTs under combined temperature and current stressing

Abstract Reliability tests at different ambient temperatures and biasing conditions have been performed on GaInP/GaAs heterojunction bipolar transistors. The epitaxial layer structure of the transistors has been grown by MOVPE, device processing utilized a triple mesa approach to access the base and collector regions and to perform interdevice isolation. A GaInP ledge structure suppresses excessive surface recombination currents. Reliability tests demonstrated a characteristic degradation behaviour of the transistors. It consists of a burn-in phase at the beginning of lifetime, followed by a rather stable phase with only minor degradation and a rapid decay of performance at the end of lifetime. It could be shown that the course of degradation and burn-in with time strongly depends on the parameters of reliability testing. Furthermore there is an indication that reliability also depends on crystal growth technology of the GaAs substrates. A device lifetime (mean time to failure, MTTF) of up to typically 3×10 7 h could be determined for a collector current density of 1×10 5 A /cm 2 and a junction temperature of 125°C.