High temperature optical properties of cadmium telluride

Abstract

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.

Characterization of vacuum evaporated CdTe thin films prepared at ambient temperature

“…Mullins et al [32] found E e ¼ 9 70:4 meV for a wafer of CdTe, which is too much smaller than our values. The difference between our results and their result may be due to the difference in preparation techniques and film thickness.…”

Correlation of microscopic grain evolution in post‐CdCl 2 annealing and performance of CdS/CdTe thin‐film solar cells fabricated using pulsed laser deposition

“…b is listed in Table . The E U increases monotonically from about 27 meV before annealing to 29 meV after 15 min annealing, illustrating a gradual increase in the structural disorders in the CdTe film or its surface . Interestingly, this trend is accelerated at longer annealing times beyond 15 min.…”

“…a. After annealing, changes in the tail of absorption band where residual absorption is anticipated are observed and can be characterized by the Urbach energy E U . According to the Urbach rule, the optical absorption coefficient α can be obtained by …”

Nondestructive Investigation of Heterojunction Interfacial Properties Using Two-Wavelength Raman Spectroscopy on Thin-Film CdS/CdTe Solar Cells

“…The minimum T of the visible light at wavelengths <800 nm is about 15%, for both types of samples, which is consistent with the absorption anticipated for the CdTe films with 1.2 microns thickness. 15 However, different absorption edges are clearly seen at the wavelength range of 810–840 nm for the as-deposited and 830–860 nm for cell samples, respectively.…”