Defect characterization in cadmium telluride and cadmium-zinc-tellurium crystals

Intrinsic defects and impurities in undoped CdTe and Cd_1−x Zn_xTe semiconductor compounds have been investigated using thermally stimulated spectroscopy with the general aim of identifying and then understanding the effects of the defects on the electrical and optical properties of these compounds. In order to identify and understand the effects of these defects (trapping levels), the samples were subjected to room temperature deformation, high temperature annealing, and dopants diffusion. The samples were always analyzed before and after any process. It is found that the trapping levels observed at ∼61 K and ∼114 K with thermal ionization energies of 0.12 ± 0.01 eV and 0.23 ± 0.01 eV and trapping cross-sections of 4.7 × 10−16 and 7.8 × 10−17 cm2 are associated with the isolated first and second ionized state of the cadmium vacancy, while trapping levels observed at ∼51 K and ∼94 K with thermal ionization energies of 0.09 ± 0.01 eV and 0.18 ± 0.01 eV and trapping cross-sections of 9.3 × 10 −17 and 6.8 × 10−17 cm2 are associated with first and second states of the isoelectronic oxygen-cadmium vacancy complex (V_Cd-O_Te) respectively. In addition, we found that deep level trapping states located near the middle of the band gap (in the region between 230 K and 267 K) in undoped as grown CdTe are related to the tellurium antisite-cadmium vacancy complex (Te_Cd-V _Cd) where the lowest thermal ionization state is 0.78 ± 0.01 eV. The thermal ionization energies (transition energies) were extracted using variable heating rate and/or initial rise methods. Our results have been reinforced with theoretical calculations using linearized augmented plane wave (LAPW) within the local density approximation (LDA). Also, from our room temperature deformation, we have found evidence of three levels of dislocation defects in CdTe crystals. The first two energy levels, with ionization energies of E1 = 0.06 ± 0.01 eV and E2 = 0.38 ± 0.01 eV are due to Cd dislocations. The third deeper level, with ionization energy of E3 = 0.49 ± 0.01 eV, is related to Te dislocations. In addition, we have found that the intensity of the induced dislocations, photoconductivity, and resistivity of the crystals are proportional to the deformation rate and the direction of the applied compression load. The annealing result showed that the applied load did not reach the yield point of the crystals; therefore, the induced deformation is elastic.