COMPOSITION AND TEMPERATURE-INDUCED EFFECTS ON THE PHONON-SPECTRA OF NARROW-BAND-GAP HG1-XCDXTE

Compositional and temperature-dependent Raman and infrared spectroscop ies on the narrow-band-gap II-VI alloy, Hg1-xCdxTe (0 less than or equ al to x less than or equal to 0.29), are reported in this paper. Raman measurements over this composition range confirm the two-mode behavio r of the optical phonons in the alloy, with the frequency positions ex hibiting a monotonic change with the alloy composition x. A resonant e nhancement of the HgTe-like forbidden longitudinal-optic mode is obser ved near the E(1) band gap of the alloy. Alloy induced perturbations o n the electronic states lead to a smearing and a weakening of the reso nance with increasing alloy composition. The optical phonons in this s mall band-gap alloy exhibit anomalous frequency shifts as a function o f temperature vis-g-vis normal wide-band-gap semiconductors. This anom aly is attributed to the strong electron-phonon interaction in narrow- band-gap systems, which overshadows the dominant anharmonic (phonon-ph onon) interaction in usual semiconductors. A detailed compositional de pendent second-order Raman spectra is also reported.