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

We present the results of experimental determination of the fundamental band gap (${\mathit{E}}_0$) and the spin-orbit split-off energy gap (${\mathrm{\Delta }}_0$) 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 ${\mathrm{\Gamma }}_8^{\mathit{V}\mathrm{-}}$ ${\mathrm{\Gamma }}_6^{\mathit{C}}$ and ${\mathrm{\Gamma }}_7^{\mathit{V}\mathrm{-}}$ ${\mathrm{\Gamma }}_6^{\mathit{C}}$ transitions in PR spectra allow us to determine the ${\mathit{E}}_0$ and ${\mathit{E}}_0$+${\mathrm{\Delta }}_0$ 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 ${\mathrm{\Delta }}_0$ 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)=1.766–6.96×${10}^{\mathrm{-}4}$ ${\mathrm{T}}^2$/(281+T) eV.