Thermal characteristics of InP, InAlAs, and AlGaAsSb metamorphic buffer layers used in In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors grown on GaAs substrates

Abstract

In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors (HBTs) were grown metamorphically on GaAs substrates by molecular beam epitaxy. In these growths, InAlAs, AlGaAsSb, and InP metamorphic buffer layers were investigated. The InAlAs and AlGaAsSb buffer layers had linear compositional grading while the InP buffer layer used direct binary deposition. The transistors grown on these three layers showed similar characteristics. Bulk thermal conductivities of 10.5, 8.4, and 16.1 W/m K were measured for the InAlAs, AlGaAsSb, and InP buffer layers, as compared to the 69 W/m K bulk thermal conductivity of bulk InP. Calculations of the resulting HBT junction temperature strongly suggest that InP metamorphic buffer layers should be employed for metamorphic HBTs operating at high power densities.