Temperature dependence of lattice vibration spectra for Hg _1-xZn_xTe alloys

The far-infrared reflection spectra of Hg_1-xZn_xTe crystals with various composition x have been measured at temperatures ranging from 90 to 295 K in the wavenumber region of 60 to 450 cm^-1. In all but the pure compounds, HgTe and ZnTe, a two TO phonon structure is clearly observed. The optical phonon frequencies are well determined by Kramers-Kronig integrations and dynamic dielectric function fitting. As the temperature is increased, the lattice vibration frequencies of the ZnTe-like optical mode decreases in the composition range x<or=0.388. A similar situation is found between the temperature dependence of the frequencies of the HgTe-like TO lattice vibration mode and the temperature dependence of energy gap. This indicates that there is a correlation between the HgTe lattice vibration mode and the electronic structure of Hg_1-xZn_xTe alloys. The approaches which concern the temperature dependence of electronic states and lattice vibration in semiconductors are discussed.