Suppression of the burn-in effect in InGaP/GaAs heterojunction bipolar transistors by constant period of voltage stress

摘要

Two significantly abrupt increases of dc current gain (β) at the opposite extremes of base-emitter voltages (V_(be)) linked by a relatively slight increase of β in the range of 1.25≤V_(be)≤1.75 V are found in InGaP/GaAs heterojunction bipolar transistors (HBT's). It has been proved that the burn-in effect directly causes the second abrupt increase of β occurring at V_(be)>1.75 V instead of elsewhere. In addition, choosing V_(be)>1.75 V, a higher base-emitter voltage results in a faster increase rate with improvement in current gain transient. Based on these observations, a constant period of voltage stress (CPVS) with V_(be)=2.0 V and V_(ce)=3.0 V for 5 min with a specific choice of V_(be)>1.75 V (the voltage range corresponding to the second abrupt increase of β) is thus applied to promote the electrical performance of HBT's. After applying a CPVS, the burn-in effect is substantially suppressed without showing any second abrupt increase of current gain. Although the current measured under both reverse and forward biases is greatly reduced for the base-emitter junction, a CPVS slightly degrades the electrical properties of a base-collector junction. Also, it has been proved that bulk recombination, rather than the surface recombination current, the base contact recombination, or the space-charge recombination, is the dominant base current component causing the burn-in effect. The electrical improvement of the base-emitter junction is due to the annihilation of H-related traps in the base region after a CPVS. Once H~(-) ions form, we propose that these ions are too fast to drift toward the base-collector junction under the reverse bias of the base-collector voltage. After migration through the extrinsic base region, H~(-) ions are supposed to be trapped near the base-collector space region, which results in the degradation of the base-collector junction after a CPVS.