Study of surface Fermi level and surface state distribution in InAlAs surface-intrinsic-n+ structure by photoreflectance

Abstract

The built-in electric field and surface Fermi level in the InAlAs surface-intrinsic-n+ structures were studied by room-temperature photoreflectance. The samples were grown by molecular beam epitaxy with an undoped layer thickness of 1000 Å. The undoped layer was subsequently etched to 800, 600, 400, and 200 Å. Different chemical solutions were used in the etching process and the built-in electric field is found independent of the etching process. While the surface Fermi level, in general, varies with the undoped layer thickness, there exists, for each Al concentration, a certain range of thicknesses within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we conclude that the surface states distribute over two separate regions within the energy band gap and the densities of surface states are as low as 1.02±0.05×1011 cm−2 for the distribution near the conduction band and 2.91±0.05×1011 cm−2 for the distribution near valence band.