Neutron irradiation effects in InP/InGaAs single heterojunction bipolar transistors
In this paper we report the effects of epi-thermal and high energy neutron irradiation on the DC characteristics of InP/InGaAs heterojunction bipolar transistors. Significant current gain degradation and collector-emitter offset voltage V/sub CE,off/ shift are the two predominant effects observed on the devices irradiated up to /spl sim/10/sup 15/ n/cm/sup 2/. The current gain degradation is attributed to the increasing base current due to the increased recombination and tunnel-assisted trapping components. The V/sub CE,off/ shift is explained by the growing base-collector (B-C) junction current caused by the defects introduced in the B-C space charge region (SCR). High, n>2, values of the base current ideality factor are modeled using the Shockley-Read-Hall (SRH) recombination and tunnel-assisted trapping in the base-emitter (B-E) SCR. Finally, devices with the higher emitter perimeter-to-area (P/A) ratio (smaller emitter) showed less degradation than the larger devices, suggesting that the degradation is primarily due to the change of the bulk properties.