Abstract
Nonuniform distributions of deep levels in semi-insulating (S.I.) LEC GaAs are investigated by photoluminescence measurements at 4.2 K. Two emission bands at 0.65 and 0.80 eV always appear in S.I. crystals. The intensity profile for the 0.65–eV band is U- or W-shaped along a wafer diameter, corresponding to the etch-pit-density (EPD) profile, while that for the 0.80–eV band shows an inverse profile with respect to the EPD profile. This profile is strong evidence for the idea that the 0.65–eV band is associated with the main electron trap (EL2) present in S.I. crystals. The origin of the 0.80–eV band is considered to be the microdefects generated dominantly in the low-dislocation-density region.