Spectroscopic-ellipsometry (SE) and thermoreflectance (TR) spectra of the defect-chalcopyrite-type semiconductor $\mathrm{Cd}{\mathrm{In}}_2{\mathrm{Te}}_4$ have been measured in the 1.2–5.2 and $1.0–6.0\mathrm{eV}$ photon-energy ranges, respectively. The measurements were carried out at $T=300\mathrm{K}$ (SE) and from $30\text{to}300\mathrm{K}$ (TR). The experimental SE and TR spectra reveal distinct structures at energies of the $E_0–E_{10}$ critical points (CP’s). From the band-structure calculations, these CP’s are assigned to specific points in the Brillouin zone. The temperature variation of the CP parameters is also determined and analyzed using (i) the Varshni equation and (ii) an analytical four-parameter expression developed to take into account the effect of band gap shrinkage in semiconductors. The analysis provides the lowest direct band gap energy and temperature coefficient of $\mathrm{Cd}{\mathrm{In}}_2{\mathrm{Te}}_4$. We find $E_0=1.27\mathrm{eV}$ $(T\to 0\mathrm{K})$ and $d{E}_0∕dT=-5.0\times {10}^{-4}\mathrm{eV}∕\mathrm{K}$ $(T=300\mathrm{K})$, respectively. The values of $E_0$ for the family of the $\mathrm{II}\text{−}{\mathrm{III}}_2\text{−}{\mathrm{VI}}_4$ semiconductors are then generalized using the molecular weights of compounds.

• Received 14 March 2007

DOI:https://doi.org/10.1103/PhysRevB.76.035202