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

The dielectric function epsilon of CdTe is deduced from spectroscopic ellip sometry measurements performed from 0.7 to 5.5 eV. For the first time epsil on is given for temperatures increasing from 20 to 370 K. epsilon variation s with photon energy are analysed within the standard critical point model (SCP). The variations, with temperature, of the CP parameters are given, di scussed 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 con tribution of this bound state decreases with T but remains high at room tem perature. The transition at E-1 is likely to correspond to a quasi bound st ate 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.