Photoreflectance study of surface Fermi level in molecular beam epitaxial grown InAlAs heterostructures

We have studied the band gaps and the surface Fermi level positions of a series of In1−xAlxAs surface-intrinsic-n+ structures at room temperature by photoreflectance. Experiments demonstrated that over aluminum concentrations of 0.42–0.57, the surface Fermi level is not pinned at midgap, as commonly believed, but instead varies, respectively, from 0.50±0.01 to 0.81±0.01 eV below the conduction band edge.