The surface and interface electronic structure of mismatched InxAl1-xA
s epitaxial layers grown by molecular beam epitaxy on InP have been in
vestigated using surface photovoltage spectroscopy. The crystalline st
ructure of the epilayers was also examined by double-crystal x-ray dif
fraction. For coherently strained layers, only a few gap states are id
entified. Highly strained samples with inferior crystalline quality, a
s judged by a broadened x-ray diffraction peak and the absence of Pend
ellosung fringes, display a rich spectrum of states in the band gap. S
ome of the states are close to the surface while others are located in
the vicinity of the InAlAs/InP heterointerfaces. (C) 1995 American In
stitute of Physics.