Quality improvement of CdMnTe:In single crystals by an effective post-growth annealing
Introduction
Cd1−xMnxTe (CMT) has been demonstrated to be a promising candidate for radiation detector application due to its wide band-gap, high resistivity, and good electron-transport properties [1], [2], [3]. It can be used for IR detectors, solar cells, optical isolators and spintronic devices [4], [5]. Specially, CMT can be used to fabricate gamma-ray detectors with high quality because it is possible to grow large single crystals with homogeneous composition theoretically [6]. However, as-grown CMT crystals usually have many defects, such as Cd vacancies, Te inclusions, twins and impurities, which will hinder its application on radiation detector [7]. Therefore, an effective post-growth annealing need to adopt to improve the quality of CMT crystals. In previous studies, several annealing methods were used for CdZnTe crystals, such as Cd (Cd/Zn) atmosphere and Te atmosphere [8], [9], [10], [11], [12]. However, few researches were involved in the annealing of CMT crystals [13], [14]. In these methods, the crystals and the raw materials are at different locations and have different temperatures. The vapor pressure in the location of the crystals is hard to control precisely. Meanwhile, the crystals and the raw materials are far apart, which results in a slow diffusion of the raw materials.
In this paper, we proposed an annealing method in which CMT crystals were covered by CMT powders with the same composition. It is the first time to apply this method to CMT crystals. The effects of annealing time on the properties of CMT crystals were investigated. The performance of detectors was also discussed.
Section snippets
Experimental
A Cd0.9Mn0.1Te:In single crystal ingot grown by the modified vertical Bridgman method (MVB) were chosen for annealing treatment. The concentration of In was 5×1017 atoms/cm−3. CMT wafers were cut from the ingot along (111) face and then diced into small slices with the size of 5×5×2 mm3. The resistivity of CMT:In slices was in the order of 109 Ω cm. Before annealing, all the slices were polished mechanically with MgO suspension and then etched with 5% bromine in methanol (Br2–MeOH) for 2 min to
Results and discussion
The typical IR microscope images (IRM) of as-grown and annealed CMT:In slices are given in Fig. 2. The observation is in situ. The density of Te inclusion are counted in several regions, selected randomly on slices. Their mean values are adopted in our analysis. From Fig. 2A–C, for as-grown CMT:In slices, the density of Te inclusions is about (6−7)×104 cm−2. The size of Te inclusions is about 1–15 μm. And the inclusions are mainly hexagonal. After 30 h, 60 h and 120 h annealing, the densities of Te
Conclusion
CMT:In single crystals were annealed by coating with CMT powders which had the same composition to improve crystal quality. The effects of annealing time on the crystal quality and physical properties of CMT:In crystals were investigated. After annealing, the density of Te inclusions decreased obviously. The FWHM of X-ray rocking curve decreased and the corresponding intensity of diffraction peak increased after annealing. The resistivity and IR transmittance of the annealed CMT:In crystals was
Acknowledgment
This work was supported by the China Postdoctoral Science Foundation (Grant No. 2014M550509), the National Natural Science Foundation of China (Grant Nos. 51201297, 51402022 and 51402023), the fund of the State Key Laboratory of Solidification Processing in NWPU (No. SKLSP201514), the Natural Science Basic Research Plan in Shaanxi Province of China (Nos. 2014JQ6217, 2015JQ5144 and 2015JQ2049) and also supported by Special Fund for Basic Science Research of Central Colleges of Chang’an University
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