Electronic structure and optical properties of CdTe rock‐salt high pressure phase

Abstract This paper reports on optical absorption and reflectance measurements in thin CdTe samples up to 15 GPa. All studied samples become virtually opaque at the pressure transition between the zinc‐blende and rock‐salt phases (3.9 GPa). As pressure increases up to 10 GPa, a relative transparency region is observed between 1.2 eV and 2.4 eV, whose high energy edge shifts to higher photon energies. Above 10 GPa the transparency region gradually shrinks and disappears at about 11 GPa. The low energy side of the absorption spectrum is attributed to free carrier absorption, as electronic structure calculations show that rock‐salt CdTe is a semimetal or a low gap semiconductor. Band filling effects lower the band‐to‐band absorption coefficient and give rise to a “transparency” range, whose upper energy side is assigned to the direct transition at the Γ point, on the basis of its pressure coefficient. The shrinking and disappearance of the transparency region, along with a large increase of the reflectance in the mid infrared, is interpreted as the occurrence of a phase transition to the Cmcm metallic phase.