Temperature dependence of the dielectric function and of the parameters of critical point transitions of CdTe

The dielectric function epsilon of CdTe is deduced from spectroscopic ellipsometry measurements performed from 0.7 to 5.5 eV. For the first time epsilon is given for temperatures increasing from 20 to 370 K. epsilon variations with photon energy are analysed within the standard critical point model (SCP). The variations, with temperature, of the CP parameters are given, discussed and compared with known data. For T < 80 K the dielectric response is completely governed by the exciton near the fundamental gap E-0. The contribution of this bound state decreases with T but remains high at room temperature. The transition at E-1 is likely to correspond to a quasi bound state interacting with the continuum in the entire temperature range studied. Only one critical point is seen in the vicinity of E-2 which behaves like a two dimensional transition at a saddle point. The weak variations of the spin-orbit splittings Delta(0) and Delta(1) with temperature are explained as resulting from the choice of lineshapes used to fit experimental data. (C) 1999 Elsevier Science B.V. All rights reserved.