Optical and structural characterisation of CdTe crystals grown by physical vapour transport and Bridgman methods

The structural and optical properties of cadmium telluride crystals have been studied by means of X-ray diffraction and SEM-cathodoluminescence techniques. CdTe crystals were grown from the melt by a modified vertical Bridgman method and by physical vapour transport, from a 7N source material and without incorporation of any doping elements. The high resistivity required for the technological applications of this material was obtained only by controlling the stoichiometric ratio between Cd and Te. The crystalline quality of the samples was first checked from the FWHM of the high-resolution X-ray rocking curves. The X-ray topographies reveal an increasing defects density in the low resistivity crystals in addition to the presence of a large number of low angle grain boundaries. The low temperature luminescence spectra show the same emission bands for all the crystals studied except for the 1.4 eV band absent in the p-type Bridgman grown samples.