High temperature optical properties of cadmium telluride

• Published in: Journal of applied physics 1997-05, Vol.81 (9), p.6374-6379
• Main Authors: Mullins, J. T., Carles, J., Brinkman, A. W.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.364371

The high temperature optical properties of cadmium telluride have been studied at temperatures up to 1104 K by measurement of the incandescence spectra from a wafer of that material. These measurements provided information equivalent to that of a transmission experiment and allowed the optical absorption spectra of the material to be determined using a theoretical expression for the refractive index and its dispersion with wavelength modified to account for the effect of temperature. This analysis required only a knowledge of the temperature dependence of the fundamental gap of cadmium telluride. Absorption by intrinsic carriers was not found to be significant at photon energies in the region of the fundamental gap even at such elevated temperatures and accordingly the near band-edge absorption was clearly discernable. As is typical in II-VI compound semiconductors, a disorder related exponential absorption (Urbach) tail was observed below the fundamental (mobility) gap and it was to such values of the absorption coefficient that this experiment was sensitive for the relatively thick sample used here. The absorption data were well fitted by assuming the energy gap to have a linear temperature coefficient of −0.34±0.02 meV K−1 and determining the absorption spectra self-consistently with that temperature dependence. At very low values of absorption, however, the condition of the sample surface dominated the spectra. Such measurements may have application in the in situ monitoring of the bulk growth of CdTe by vapour phase techniques, providing information regarding temperature, structural disorder, and surface stoichiometry.