Concentrations of total ionized point defects, neutral and ionized EL2, carbon acceptor, and other shallow donor and acceptor levels in as-grown and as-annealed semi-insulating GaAs crystals were characterized using nuclear magnetic resonance, multiwavelength near-infrared photoabsorption, and Fourier-transformed infrared photoabsorption. In as-grown crystals, shallow donors (XD) and acceptors (XA) of about 2×10 15 cm-3 concentration were found to exist. The net donor concentration (NXD - NXA) of these levels showed an excellent positive correlation with the carbon acceptor in its distribution within the wafer, implying the donor's carbon-acceptor-related origin. An anneal at 850 °C for 24 h diminished these levels. By regarding the intrinsic donor as VAs, the improvement in electrical uniformity during ingot annealing is explained in terms of an annihilation of both intrinsic acceptors and precursors for SiAs acceptors.
ASJC Scopus subject areas
- Physics and Astronomy(all)