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    Electronic structure and optical properties of CdTe rock-salt high pressure phase
    (Wiley-V C H Verlag Gmbh, 2003) Güder, HS; Gilliland, S; Sans, JA; Segura, A; González, J; Mora, I; Muñoz, V
    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 r 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.
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    Pressure and temperature dependence of the band-gap in CdTe
    (Wiley-V C H Verlag Gmbh, 2003) Gilliland, S; González, J; Güder, HS; Segura, A; Mora, I; Muñoz, V
    In this paper we report on isothermal compression measurements (up to 5 GPa and 500 K) of the optical absorption edge of 1 mum epitaxial layers of CdTe growth by metalorganic chemical vapor deposition (MOCVD) on GaS substrates. The isothermal blue shift under pressure of the direct energy gap (Gamma(15)(v) --> Gamma(1)(c)) in the zinc-blende phase is about 7.1 x 10(-2) eV GPa(-1) and is found to be independent of temperature within the experimental errors. The isobaric red shift in the stability range of the zinc-blende phase is about -3.76 x 10(-4) eV K-1. Regarding the phase transitions, no discontinuity in the energy gap has been found in the narrow pressure range where the cinnabar phase can be present. The transition pressure to the NaCl-type structure in CdTe is found to decrease with increasing temperature (294-500 K) following the law P-t = 4.1 GPa - 6.6 x 10(-3) (T - 273) (K).