Reduction and origin of electron and hole traps in GaAs grown by molecular-beam epitaxy

Deep-level transient spectroscopy (DLTS) is shown to be a simple and powerful diagnostic tool for monitoring the cleanliness of a molecular-beam epitaxy (MBE) system and for determining optimum growth conditions. GaAs, grown by MBE under ideal conditions, is essentially free from electron and hole traps, and any contamination introduced by impurities in the sources, or resulting from substandard growth conditions, is reflected by the presence of traps as detected by DLTS. We find that the origin of dominant MBE-GaAs hole traps and electron traps M1, M3, and M4 is the complexing of unknown chemical impurities and defects in the crystal. Impure arsenic is the major source of such chemical impurities, although these impurities can originate from other sources as well, such as the molybdenum substrate holding blocks. These chemical impurities do not appear to be the shallow donors or acceptors. Electron traps M5–M8 are due to crystal defects.