Abstract
We have developed an InGaP/GaInAsN/GaAs double heterojunction bipolar transistortechnology that substantially improves upon existing GaAs-based HBTs. Band-gapengineering with dilute nitride GaInAsN alloys is utilized to enhance a variety of key devicecharacteristics, including lower operating voltages, improved temperature stability andincreased RF performance. Furthermore, GaInAsN-based HBTs are fully compatiblewith existing high-volume MOVPE and IC fabrication processes. While poorlifetimes have limited the applicability of dilute nitride materials in photovoltaicapplications, we achieve minority carrier characteristics that approach those ofconventional GaAs HBTs. We have found that a combination of growth algorithmoptimization and compositional grading are critical for improving minority carrierproperties in GaInAsN. In this work, we characterize the impact of both carbon andnitrogen doping on minority carrier lifetimes in GaInAsN base layers. Minoritycarrier lifetimes are extracted from direct measurements on bipolar transistordevice structures. Specifically, lifetime is derived from the DC current gain, orβ, taken in the bias regime dominated by neutral base recombination. Lifetimesextracted using this technique are observed to be inversely proportional to bothcarbon and nitrogen doping. As with conventional C-doped GaAs HBTs, currentsoaking (i.e. burn-in) is found to have a significant impact on GaInAsN HBTs.While we can replicate poor as-grown lifetimes consistent with those reported inphotovoltaic dilute nitride materials, our best material to date exhibits nearly30 × higher lifetime after current soaking.
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