Optical emission properties of semi-insulating GaAs grown at low temperatures by molecular beam epitaxy

We have used cathodoluminescence (CL) and photoluminescence spectroscopy to observe deep-level states in GaAs grown at low-substrate temperatures by molecular beam epitaxy (LT GaAs) and the evolution of these states upon annealing. The as-grown material shows intense deep-level emissions which can be associated with an excess concentration of arsenic, mostly present as As-antisite and As-interstitial defects. These emissions subside with annealing for a few minutes at temperatures above 450°C. CL measurements clearly show a dramatically reduced concentration of traps in the post-growth 600°C annealed material. Additional measurements carried out on As/GaAs systems indicate a high surface-recombination velocity for these interfaces. These results account for a diminished role of electronic point defects in controlling the insulative behavior of LT GaAs and strongly supports a "buried" Schottky barrier model, which involves ultrafast recombination of carriers at surfaces of embedded arsenic clusters formed during the annealing processing of LT GaAs.