Temperature dependence of the band gap of Cd1−xZnxTe alloys of low zinc concentrations

Abstract

The temperature dependence of the fundamental band-gap E0 of Cd1−xZnxTe alloys with zinc concentrations in the 0 to 0.3 range has been determined by modulated photoreflectance (PR). E0 is found to vary from 1.511 eV for x=0.00 to 1.667±0.008 eV for x=0.3, at room temperature and from 1.602 eV at x=0.00 to 1.762±0.004 eV for x=0.3 at 10 K. The measured broadening parameters Γ have values between 25 and 45 meV at room temperature and decrease monotonically to values around 5 meV or smaller at 10 K. The temperature dependence of the observed band gap energies is well described by the well known Varshni formula E(T)=E(0)−AT2/(T+Θ) for all samples studied. The PR temperature broadening is well understood assuming that it results from the scattering of the excitonic electron-hole pair responsible of the band-to-band transition PR signal off LO phonons.