Characterization of semiconductors by photoluminescence mapping at room temperature

Abstract

Room-temperature photoluminescence (PL) mapping technique is used to characterize the distribution of deep levels in semiconductor wafers. The key points to achieve this are a weak excitation condition, high stability of the apparatus, and adequate surface treatment of samples. The deep-level PL associated with the native midgap donor EL2 in semi-insulating GaAs crystals and that associated with the thermal donor (TD) in heat-treated Czochralski-grown Si crystals are detectable at room temperature. The mappings of the EL2-related 0.65 eV band on GaAs wafers indicate a high degree of correlation with the EL2 absorption. Using this technique, semi-quantitative mapping of the EL2 level is realized. The mapping of the TD-related 0.7 eV band shows a characteristic growth-striation pattern, corresponding to the resistivity variation. The present technique makes it possible to evaluate the nonuniform distribution of deep levels in the device-active surface layer of as-received wafers, in air, nondestructively, and with a high spatial resolution.