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 x 10 sup (15) electrons/cm sup 2. The devices show an increase in common-emitter current gain (h sub (fe)) at low levels of dose (= 10 sup (15) electrons/cm sup 2) and a gradual decrease in h sub (fe) and an increase in output conductance for higher doses. The decrease in h sub (fe) is as much as ~80% at low base currents (~ 10 mu A) after a cumulative dose of 14.8 x 10 sup (15) electrons/cm sup 2. The observed degradation effects in collector current-voltage characteristics are studied quantitatively using a simple SPICE-like device model. The overall decrease in h sub (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.