Photoreflectance spectroscopy of wurtzite CdS

Photoreflectance (PR) spectra have been measured to determine the lowest direct-band edge E-0alpha (alpha=A, B, and C) of wurtzite CdS single crystal in the temperature range T=13-300 K for both Eperpendicular toc and Eparallel toc polarizations. The measured PR spectra can be interpreted by the three-dimensional (3D) excitonic plus one-electron line shapes over the entire temperature range. The temperature dependence of the excitonic and critical-point parameters (energy, amplitude, and broadening parameter) have been determined and analyzed using the Varshni [Physica (Amsterdam) 34, 149 (1967)] equation and an analytical four-parameter expression recently developed for the explanation of the band-gap shrinkage effect in semiconductors. The 3D- exciton binding energies have also been determined to be 27 (A), 31 (B), and 30 meV (C), respectively. (C) 2002 American Institute of Physics.