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 (E₀) and the spin-orbit split-off energy gap (Δ₀) 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 Γ₈^V-Γ₆^C and Γ₇^V-Γ₆^C transitions in PR spectra allow us to determine the E₀ and E₀+Δ₀ band-gap energies. We found that zinc-blende CdSe has a fundamental band gap E₀ of 1.661 eV and a spin-orbit split-off gap Δ₀ of 0.42 eV at room temperature (295 K). The fundamental band gap E₀ 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 E₀(T)=1.766–6.96×10^-4 T²/(281+T) eV.