Generation-recombination centers in CdTe:V
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ICONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Generation–Recombination Centers in CdTe:V L. A. Kosyachenko, S. Yu. Paranchich, Yu. V. Tanasyuk, V. M. Sklyarchuk, E. F. Sklyarchuk, E. L. Maslyanchuk, and V. V. Motushchuk Chernovtsy National University, Chernovtsy, 58012 Ukraine Submitted September 6, 2002; accepted for publication October 4, 2002
Abstract—Generation–recombination currents in surface-barrier structures based on vanadium-doped CdTe are investigated. The level depth and the capture cross section of the centers responsible for the most efficient generation–recombination processes in the samples examined are determined. © 2003 MAIK “Nauka/Interperiodica”.
1. INTRODUCTION Cadmium telluride is one of the most well-studied II–VI compound semiconductors. It is a promising material for photodetectors, solar cells, and filters for the infrared spectral range. For several decades, CdTe and Cd1 – xZnxTe alloys (x ≈ 0.1) have been utilized in X-ray and γ-ray detectors [1, 2]. Another potentially important application is related to the use of CdTe as a photorefractive material in optical memory and information-processing systems. Development of CdTe-based devices calls for the solution of several important problems. One of these is determining the parameters of impurity- and defectrelated levels in this semiconductor. With respect to photorefractivity-based devices, deep levels of V impurity are of interest. Vanadium forms several recombination and trapping levels in the band gap [3]. A number of techniques (electrical, optical, luminescence, etc.) were used to examine the properties of CdTe:V and Cd1 – xZnxTe (x ≈ 0.1) in relation to the influence V doping; however, the parameters of these levels are not accurately known. In particular, this pertains to deeplevel generation–recombination centers in the CdTebased material. Consider, for example, deep levels in the energy range (Eg/2) ± 0.1 eV (0.65–0.85 eV): one study revealed three levels located at 0.75, 0.77, and 0.78 eV [4]; two levels (at 0.76 and 0.79 eV) were found in another study [5]; and no such levels were found in a third one [6]. It is quite possible that differences in level positions reported by different authors are due to limited accuracy of the measurements rather than to a different nature of the levels involved. In this paper, we report on the study of electrical properties of CdTe:V surface-barrier structures; the results presented make it possible to determine, with sufficiently high accuracy, (±0.01 eV) the level depth and the capture cross section of the centers involved most efficiently in the generation–recombination processes in CdTe:V. We also believe that the results related to the mechanisms of charge transport, which demonstrate very good agreement between the calculations and the experimental data, are of interest in themselves.
2. SAMPLES Single crystals of CdTe:V were grown by the vertical Bridgman method in a quartz container. The concentration of V, which was loaded into the cell simultaneously with high-purity Cd and Te, wa
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