Growth of high quality AlGaAs/GaAs heterostructures by gas source molecular-beam epitaxy

Abstract

Unintentional p-type doping of GaAs films grown by gas source molecular-beam epitaxy (GSMBE) was reduced to 2×1014 cm−3 with a room-temperature hole mobility of 490 cm2/V s. Intentional Si doping of GaAs films grown by GSMBE, using an elemental Si source, yielded controlled carrier concentrations from 7×1014 to 8×1018 cm−3 with 77 K mobilities from 62 700 to 2 500 cm2/V s. Residual carbon incorporation was reduced in AlGaAs by growing at 560 °C and using tri-isobutylaluminum such that 77 K two-dimensional electron gas mobilities as high as 88 600 cm2/V s were obtained. Our study of using trimethylgallium or a graphite filament as a carbon source for p-type doping indicates that doping levels can be controlled in the range of 5×1016–1.5×1020 cm−3 with good hole mobility and surface morphology. Preliminary results show an undetectable diffusion of carbon in the AlGaAs/GaAs heterojunction bipolar transistor (HBT) structures with a base doping level as high as 1.5×1020 cm−3, using carbon as a p-type dopant, grown at a substrate temperature of 600 °C and annealed at 700 °C for 30 min.