Degradation of InGaAs/InP double heterojunction bipolar transistors under electron irradiation

The dc characteristics of InGaAs/InP double heterojunction bipolar transistors (DHBTs) are studied under high-energy (~1 MeV) electron irradiation up to a fluence of 14.8×10¹⁵ electrons/cm ². The devices show an increase in common-emitter current gain (h_fe) at low levels of dose (<10¹⁵ electrons/cm²) and a gradual decrease in h_fe and an increase in output conductance for higher doses. The decrease in h _fe is as much as ~80% at low base currents (~10 μA) after a cumulative dose of 14.8×10¹⁵ electrons/cm². The observed degradation effects in collector current-voltage (I-V) characteristics are studied quantitatively using a simple SPICE-like device model. The overall decrease in h_fe is attributed to increased recombination in the emitter-base junction region caused by radiation-induced defects. The defects introduced in the collector-base junction region are believed to be responsible for the observed increase in the output conductance