Analysis of InP/GaAsSb DHBT failure mechanisms under accelerated aging tests

We report on the reliability of InP/GaAsSb/InP DHBTs dedicated to very high-speed ICs applications. The devices under tests were fabricated by OMMIC [1]. Accelerated aging tests under thermal stress were previously performed on the same technology and the results are detailed in [2]. In this paper, we present the accelerated aging tests under bias stress performed on 15 DHBTs up to 2000 hours. The collector current density was fixed at 400 kA/cm² with various collector-emitter voltages V_CE (from 1.5 V to 2 V) and various base plate temperature T_a (from 30°C to 120°C). The associated junction temperature range is 80-180°C. From the Gummel characteristic, we observe that the major degradation mechanism is the base current decrease for V_BE <; 0.8 V. The failure mechanism leading to the base current I_B decrease was analysed by physical simulation using TCAD. The degradation mechanism leading to the gradual decrease of the base current is linked to the emitter sidewall trap density decrease. To correctly simulate the base current during aging tests, a unique donor trap level at E_T-E_V = 1.15 eV were modified. The traps density evolution suggests a surface state improvement. Associated activation energy E_a of 0.63 eV has been extracted.