Effects of Electrical Stress on the InGaP/GaAs Heterojunction Phototransistor

Although the effects of electrical stress on the performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) have been widely studied and reported, few or no reports on the InGaP/GaAs heterojunction phototransistors (HPTs) have been published. In this paper, we discuss the phototransistor characteristics before and after the electrical stress applied at room temperature and at high temperature, and assess the effectiveness of the emitter-ledge passivation, which was found to keep the InGaP/GaAs HBTs from degrading at higher temperature or due to electrical stress. A room-temperature electrical stress was applied to the HPTs by maintaining a current density of 37 A/cm
²
for 1 h at room temperature. The electrical stress was lower by two to three orders than the stress usually applied to the HBTs for the stress study and did not cause significant decreases in the room-temperature current gain and photoresponse, but it significantly degraded the characteristics of the InGaP/GaAs HPTs at 420 K. In order to accelerate the degradation, the high-temperature stress was applied to both HPTs with and without the emitter-ledge passivation at 420 K. Although the current density was the same and the stress time was reduced to 15 min, the high-temperature stress significantly decreased the current gain and collector photocurrent of the HPT without the emitter-ledge passivation over the entire measurement temperature range of 300-420 K. The emitter-ledge passivation suppresses the recombination via defects at the emitter perimeter and is found to be more effective than that in the HBTs.