National Renewable Energy Laboratory, Golden, Colorado 80401
M.E. Raikh and E.V. Tsiper
Department of Physics, University of Utah, Salt Lake City, Utah 84112
We have applied reflectance-difference spectroscopy (RDS) to the study
of optical anisotropy in spontaneously ordered
Ga0.5In0.5P grown by metal-organic
chemical-vapor deposition. The degree of order in
Ga0.5In0.5P has been associated previously with
a shift of the band-gap energy &Delta E0 and a crystal-field
valence-band splitting &Deltac. Theoretically, both
quantities are, to first order, quadratic functions of the long-range
order parameter \eta, which varies from 0 to 1 for disordered and
perfectly ordered Ga0.5In0.5P, respectively.
The main RD spectral feature in partially ordered
Ga0.5In0.5P is a bulk-induced, asymmetric peak
at E0 with a long tail that extends well below
E0 and a sharp high-energy cutoff at
E0+&Deltac. We find experimentally and
theoretically that the intensity of this RD spectral feature is
proportional to (&Delta E0)1/2 and, therefore, is
linear with the order parameter. This makes RDS particularly useful
for measuring the optical anisotropy of high-band-gap
Ga0.5In0.5P. We also compare heterostructures
of GaAs and AlInP on Ga0.5In0.5P with uncoated
Ga0.5In0.5P in an effort to separate bulk-,
surface-, and interface-induced RD spectral features.