Determination of the fundamental and split-off band gaps in zinc-blende CdSe by photomodulation spectroscopy.

Abstract

We present the results of experimental determination of the fundamental band gap (${\mathit{E}}_{0}$) and the spin-orbit split-off energy gap (${\mathrm{\ensuremath{\Delta}}}_{0}$) of zinc-blende CdSe using photomodulation spectroscopy. The single-crystal CdSe film was grown by molecular-beam epitaxy on a (100) GaAs substrate with a ZnTe buffer layer. Photoreflectance (PR) measurements were performed on the sample at various temperatures from 10 K to room temperature. The sharp derivativelike spectral features associated with the interband ${\mathrm{\ensuremath{\Gamma}}}_{8}^{\mathit{V}\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\Gamma}}}_{6}^{\mathit{C}}$ and ${\mathrm{\ensuremath{\Gamma}}}_{7}^{\mathit{V}\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\Gamma}}}_{6}^{\mathit{C}}$ transitions in PR spectra allow us to determine the ${\mathit{E}}_{0}$ and ${\mathit{E}}_{0}$+${\mathrm{\ensuremath{\Delta}}}_{0}$ band-gap energies. We found that zinc-blende CdSe has a fundamental band gap ${\mathit{E}}_{0}$ of 1.661 eV and a spin-orbit split-off gap ${\mathrm{\ensuremath{\Delta}}}_{0}$ of 0.42 eV at room temperature (295 K). The fundamental band gap ${\mathit{E}}_{0}$ of zinc-blende CdSe has been mapped out as a function of temperature and the Varshni thermal coefficients have been determined for this material. The results yield ${\mathit{E}}_{0}$(T)=1.766\char21{}6.96\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{T}}^{2}$/(281+T) eV.