Abstract
Compositional and temperature-dependent Raman and infrared spectroscopies on the narrow-band-gap II-VI alloy, ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Te (0\ensuremath{\le}x\ensuremath{\le}0.29), are reported in this paper. Raman measurements over this composition range confirm the two-mode behavior of the optical phonons in the alloy, with the frequency positions exhibiting a monotonic change with the alloy composition x. A resonant enhancement of the HgTe-like forbidden longitudinal-optic mode is observed near the ${\mathit{E}}_{1}$ band gap of the alloy. Alloy induced perturbations on the electronic states lead to a smearing and a weakening of the resonance with increasing alloy composition. The optical phonons in this small band-gap alloy exhibit anomalous frequency shifts as a function of temperature vis-\`a-vis normal wide-band-gap semiconductors. This anomaly is attributed to the strong electron-phonon interaction in narrow-band-gap systems, which overshadows the dominant anharmonic (phonon-phonon) interaction in usual semiconductors. A detailed compositional dependent second-order Raman spectra is also reported.
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