Photoreflectance is used to investigate the band gap, built-in electric fie
ld, and surface Fermi level of a series of lattice-matched In0.52Al0.48As s
urface-intrinsic n(+) structures having different undoped layer thicknesses
. Experimental results indicate that, although the built-in electric field
depends on the undoped layer thickness, there is a range of thickness withi
n which the surface Fermi level is weakly pinned. From the dependence of el
ectric field and surface Fermi level on the undoped layer thickness, we can
determine that the surface states distribute over two separate regions wit
hin the energy band gap. The densities of the surface states are evaluated
as well. Moreover, the dependence of the built-in electric field on undoped
layer thickness is converted into the dependence of surface state density
on the surface Fermi level in order to theoretically and exactly calculate
the energy spectrum of the surface state density using a Guassian distribut
ion function. The center and width of the distribution near the conduction
band are obtained from the fitting parameters. (C) 2001 American Institute
of Physics.