Photoluminescence investigation of CdZnTe:In single crystals annealed in CdZn vapors
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nying Zhang Beijing Power Machinery Research Institute, Beijing 100074, People’s Republic of China (Received 16 December 2005; accepted 18 April 2006)
CdZnTe:In single crystals were annealed in CdZn vapors through a method involving a high-temperature step and a low-temperature step in sequence. The effects of annealing on the properties of CdZnTe:In were characterized with photoluminescence (PL) spectra. The neutral acceptor bound exciton (A0, X) peak, which was on the right shoulder of the neutral donor bound exciton (D0, X) peak, disappeared after annealing. A fine donor-acceptor pair structure and its longitudinal optical phonon replicas were clear before annealing. However, both of them became undistinguishable in the PL spectrum of annealed CdZnTe:In. The two phenomena imply that the annealing treatment can remove the impurities from CdZnTe:In wafers effectively. In addition, the intensity of Dcomplex band fell remarkably after annealing, which confirmed that Cd vacancies were well-compensated in the annealing treatment.
I. INTRODUCTION
As the most suitable material for room-temperature nuclear radiation detectors, CdZnTe (CZT) has attracted increasing interest in recent years.1–6 The modified Bridgman (MB) method is widely used to produce CZT crystals. Unfortunately, the resistivity of as-grown CZT produced by MB is somewhat lower, which limits the performance of the nuclear detectors. Previous investigations indicated that In doping noticeably improves the resistivity of CZT.2 However, due to the high partial pressure of Cd, the as-grown CdZnTe:In ingots still exhibit a high density of defects such as Cd vacancies, Te antisites, and Te precipitates. These defects seriously deteriorate the opto-electrical properties of CdZnTe:In. Annealing under certain conditions can improve the crystals’ quality and thus improve the performance of CdZnTe:In detectors.3,4 Until now, the mechanism responsible for this variation has not been identified. Photoluminescence (PL) measurement is sensitive to different energy states of semiconductors and provides abundant information about energy levels of impurities and defects, even at very low densities. Accordingly, PL spectra are very useful for understanding the variation of recombination during the annealing of CdZnTe:In. In this work, CdZnTe:In
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0219 J. Mater. Res., Vol. 21, No. 7, Jul 2006
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crystals were annealed in CdZn vapors with a hightemperature step and a low-temperature step in sequence. PL spectra were used to analyze the effects of annealing on the properties of CdZnTe:In. II. EXPERIMENTAL PROCEDURES
CdZnTe:In crystals were grown through the MB method in our laboratory. High-purity raw materials of Cd (7N), Zn (7N), Te (7N), and In (7N) were used to prevent unintended impurities. The mole ratio of Cd, Zn, and Te was 0.9:0.1:1. The concentration of In in the CdZnTe:In ingot was 15 ppm. The ingots were cut alon
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