STUDY OF SURFACE FERMI-LEVEL AND SURFACE-STATE DISTRIBUTION IN INALASSURFACE-INTRINSIC-N(+) STRUCTURE BY PHOTOREFLECTANCE

The built-in electric field and surface Fermi level in the InAlAs surf ace-intrinsic-n(+) structures were studied by room-temperature photore flectance. The samples were, grown by molecular beam epitaxy with an u ndoped layer thickness of 1000 Angstrom. The undoped layer was subsequ ently etched to 800, 600, 400, and 200 Angstrom. Different chemical so lutions were used in the etching process and the built-in electric fie ld is found independent of the etching process. While the surface Ferm i level, in general, varies with the undoped layer thickness, there ex ists, for each Al concentration, a certain range of thicknesses within which the surface Fermi level is weakly pinned. From the dependence o f electric held and surface Fermi level on the undoped layer thickness , we conclude that the surface states distribute over two separate reg ions within the energy band gap and the densities of surface states ar e as low as 1.02+/-0.05X10(11) cm(-2) for the distribution near the co nduction band and 2.91+/-0.05X10(11) cm(-2) for the distribution near valence band. (C) 1995 American Institute of Physics.