Photoreflectance studies of surface state density of InAlAs

The surface barrier height and surface Fermi level of InAlAs were investigated via photoreflectance spectra. Surface state density was then determined from the surface barrier height as a function of temperature, illumination power intensity, and intrinsic layer thickness. Results obtained from these three independent approaches all give the same conclusion, that the surface states are distributed over two separate regions within the energy band gap. Closely examining the photovoltage induced by various incident beam intensities revealed that the photovoltage effect is negligible when the illumination power intensity is below 1.0 μW/cm2.