Abstract
Multistep wafer-annealed semi-insulating GaAs wafers (MWA) are characterized using photoluminescence (PL). The PL spectra present well-resolved near-band-edge transitions, including the doublet of the neutral acceptor-bound exciton. A detailed investigation using selective pair luminescence of samples submitted to different annealings, i.e., wafer- or ingot-annealing, single or multistep, shows that carbon is the main shallow acceptor. However, for the wafer-annealed samples, two other residual impurities found in the as-grown or ingot-annealed crystals have their estimated concentrations noticeably reduced, for Zn (e.g., around 10(13) cm-3 in MWA), or are unresolved for Si. This reduction of background impurities may have direct consequences for device applications.