Effect of hydrostatic pressure on the HgTe optical phonon

We have measured the reflectivity from 20–240cm^?1 of HgTe samples at 80 K and below as a function of hydrostatic pressure to 8 kbars. The transverse optical phonon frequency was determined from a Kramers-Kronig analysis of the data. For three samples of different doping levels we find dω_TO/dp = 0.34 cm^?1 kbar^?1. The Gruneissen's parameter, γ = 1.2, is typical of values for zincblende crystals indicating that the phonon is not influenced by the narrow gap and inverted band structure. The defect oscillator at 107 cm^?1 is observed to be independent of pressure. This appears inconsistent with its identification as a phonon difference mode.