Photoluminescence of pure GaAs crystals cleaved in ultrahigh vacuum

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Abstract
Photoluminescence measurements of pure GaAs crystals cleaved in ultrahigh vacuum (UHV) are compared to those of air-cleaved reference samples. Nonradiative surface recombination and band bending are considerably reduced at the UHV-cleaved surface. We find at low temperature (∼20 K) roughly the same spectral shape and the same integrated intensity for the UHV- and air-cleaved surfaces provided we apply a factor of 10 lower excitation power density to the UHV-cleaved surface. This factor of 10 stays constant over more than five orders of magnitude of excitation density. A detailed comparison of the spectra shows that the characteristic reabsorption minimum in the free-exciton polariton luminescence is missing in the case of the UHV-cleaved surface.