Photoluminescence (PL) and selective pair luminescence (SPL) techniques were used to evaluate a large number of GaAs crystals. It was found that the results of these photoluminescence measurements, combined with data on carbon concentration obtained by local vibrational mode absorption spectroscopy, make possible an analysis of shallow impurities. Their relative concentrations were compared from seed to tail and from crystal to crystal and correlated to material resistivity. Impurities segregation in a crystal was analysed. Results of polariton line shape and intensity analysis were used in surface-related studies. Advantages of using both PL and SPL as a routine production analytical technique will be enhanced when the equipment for two-dimensional mapping of a whole GaAs wafer is completed.
We have used a series of all-optical measurements to determine shallow acceptor, shallow donor, and midgap donor (EL2) concentrations. The validity of these measurements was then tested by comparing the predicted electron density to the measured Hall density. Resonant pumping of the first excited state of the polariton sharpened the photoluminescence spectrum sufficiently to allow a reliable measurement of the shallow donor to acceptor ratio. The absolute shallow acceptor, donor, and EL2 concentrations were determined by a series of absorption and luminescence measurements. The Fermi level and hence the carrier concentration was then deduced using the three-level model of semi-insulating behavior.
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