Crystal defects and optical transitions in high purity, high resistivity CdTe for device applications

Abstract

The structural and optical properties of high purity undoped semi-insulating (SI) Cadmium Telluride (CdTe) crystals, grown by Physical Vapour Transport (PVT) and by modified Vertical Bridgman (BG) techniques have been studied. The samples were obtained from 7N source elements by direct synthesis followed by heat treatment to adjust the stoichiometry. The experimental measurements have been systematically performed using high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL) techniques, before and after the thermal annealing procedures. The CL emissions from low and high resistivity samples have been studied in order to correlate the CL bands to the presence and concentration of native defects in the crystals. Two broad luminescence bands have been found in addition to the expected emission related to the excitonic recombination. The nature of the defects involved in the transitions was studied by analysing the position of the energy levels and the relative intensity variation of the CL peaks. The effect of the thermal treatments, performed at different temperatures, on the optical and electrical properties of the specimens was also analysed.