Undoped, semi-insulating GaAs layers grown by molecular beam epitaxy

Growth of undoped layers of GaAs by molecular beam epitaxy is reported. The resistivity of these layers is consistently greater than 106 Ω cm. Low-temperature photoluminescence measurements show well resolved exciton bands characteristic of very pure GaAs. The main contaminant is identified as carbon, at an extremely low level, and the spectra are completely free of any carbon-induced defect bands. The results suggest that the high resistivity of these layers is due to reduction of the background carbon level and the resulting close compensation of residual donors.