Photoluminescence and absorption studies of defects in CdTe andZnxCd1

Abstract

We have studied at cryogenic temperatures photoluminescence features which lie more than 0.15 eV below the band edge in Zn Cd& Te (0+x 0.09) crystals. The same features, namely a defect band which lies at about 0.13 -0.20 eV below the band-gap energy and a peak at 1.1 eV, that are observed in pure CdTe samples are observed in these alloy materials. In annealed samples we observe that the 1.1-eV feature, which has been attributed to tellurium vacancies, increases with fast cooling. Increased concentrations of tellurium vacancies can be understood in terms of the phase diagram of CdTe which indicates that higher concentrations of excess Cd appear in CdTe quenched from high temperatures. We also observe an absorption transition near 1.1 eV by photothermal deflection spectroscopy (PTDS). The PTDS phase shifts show that the deep defect is a bulk effect rather than a surface effect. The welldefined absorption peak suggests that the states contributing to the 1.1-eV transition are both localized.Our results also suggest that the defect band which lies 0.13 eV below the band gap (1.48 eV in CdTe) may also be related to tellurium vacancies. However, the fact that the ratio of intensities between this defect band and the 1.1-eV feature is highly variable suggests that the relationship is not simple. The origin of the defect band and its phonon replicas remains controversial.

Heavy metal doping of CdTe crystals

“…The same behavior was assigned to the specie As in nominal pure CdTe with As as impurity [28]. Usually, emissions in this region are associated with V and related species [29].Therefore, this peak may be related to the amphoter behavior of the heavy metals, involving the specie M (with M heavy metal), and probably been associated to the dopant TABLE III ACTIVATION ENERGY FOR THE DIFFERENT PEAKS OF THE PL SPECTRA FOR EVERY DOPANT TABLE IV THERMAL ENERGY COEFFICIENT FOR THE DIFFERENT DOPANTS self-compensation. As can be seen in Fig.…”

Comparison of electrical and luminescence data for the A center in CdTe

“…In fact, the 1.4 eV band has been reported in the literature to be present in most II-VI compounds, independently of doping and growth method. 6,7,[12][13][14][15][16] This implies that there might be other native defects/complexes, extended defects or residual impurities which either emit in the spectral range 1.3-1.5 eV or form complexes with the available V Cd . Therefore, the 1.4 eV band might not be necessarily related to an actual A center.…”

“…Therefore, the 1.4 eV band might not be necessarily related to an actual A center. 6,8,13,14,17 We have studied the various components of the 1.4 eV band in order to understand which ones could be reliably attributed to the A center. The techniques we have utilized are cathodoluminescence ͑CL͒ and junction spectroscopy, such as deep level transient spectroscopy ͑DLTS͒, 18 PICTS, 19 and photo-DLTS ͑P-DLTS͒.…”

Seeded physical vapor transport of cadmium-zinc telluride crystals: growth and characterization

“…The third, broad emission region lies about 0.17 eV below the bound exciton line. Since we used undoped and high purity materials, the peak is apparently associated with cadmium vacancy related defects [13,14]. exceeded 100 only in some samples.…”

“…Considering the origin of the emission lines, the PL spectra can be divided into three regions (from right to left, Fig. 3a): (i) the bound exciton recombinations (BE) [11,12]; (ii) donor-acceptor pair (DAP) transitions [13]: and (iii) emission associated with crystal defects (DEF) [ 13,14]. The exciton nature of the edge peak (BE) of the crystals was confirmed by a superlinear dependence of the PL amplitude of the edge peak on excitation intensity.…”