SURFACE CHARACTERIZATION OF LEC SI-GAAS USING PHOTOREFLECTANCE WITH SUB-BANDGAP EXCITATION

A novel variation of photoreflectance, where the modulating beam has a photon energy that is smaller than the bandgap of the semiconductor, has been performed on SI-LEC grown Gallium Arsenide to study its surface properties. Analysis shows that the surface electric field created upon the application of the above light is sensitive to surface states and relatively insensitive to the bulk properties. The effect of various chemical treatments on the surface state density of GaAs is measured. Spectral features at energies smaller than the gap energy are observed and are assigned to shallow impurities. A mechanism for modulation of impurity absorption has been proposed.