Iodine and carbon tetrabromide use in solid source molecular beam epitaxy

Abstract

We have studied CBr4 doping of GaAs and In0.53Ga0.47As up to 2×1020/cm3, of InxGa1−xAs across the composition range from x=0 to x=1, and of GaAs and In0.53Ga0.47As on the (211)A, (311)A, (511)A, (511)B, (311)B, and (211)B planes. These data show little evidence of self-compensation in C-doped GaAs, although carbon incorporation is more efficient on the Ga-rich (n11)A surfaces. In0.53Ga0.47As shows a similar dependence of carbon incorporation on surface orientation, and also exhibits self-compensation on the As-rich (n11)B surfaces and at In molar fractions x greater than about 0.7. We have made heterojunction bipolar transistors (HBTs) with abrupt emitter-base junctions and GaAs base layers doped to 1×1020/cm3 which have useful dc current gains, and have also used in situ iodine etching for regrowth over patterned subcollectors to make operating HBTs designed for reduced base-collector capacitance. Despite using CBr4 nearly exclusively as our p-type dopant in solid-source molecular beam epitaxy for more than five years and iodine for more than two years, we have observed no persistant degradation in doped or undoped material quality as measured by photoluminescence intensity, carrier mobility, or npn heterojunction bipolar transistor HBT current gain. Photoluminescence intensity and 77 K carrier mobility have gradually improved coincident with the introduction and continued use of iodine in our system, although there is no direct evidence of causality.