Elsevier

Journal of Crystal Growth

Volume 451, 1 October 2016, Pages 194-199
Journal of Crystal Growth

Quality improvement of CdMnTe:In single crystals by an effective post-growth annealing

https://doi.org/10.1016/j.jcrysgro.2016.07.009Get rights and content

Highlights

  • An effective post-growth annealing method was used to improve the performance of CdMnTe:In crystals.

  • The density of Te inclusions decreased notably.

  • The resistivity increased even two orders of magnitude (from 109 to 1011 Ω cm).

  • The optimal annealing conditions are a temperature of 1073 K and duration of 120 h.

Abstract

In this paper, an effective annealing method in which CdMnTe:In (CMT:In) single crystals were coated with CMT powders of the same composition was used to improve the crystal quality of CMT:In crystals. The results indicated that the density of Te inclusions decreased as the annealing time increased. The resistivity and IR transmittance of annealed CMT:In crystals were enhanced obviously. The resistivity of 120 h annealed crystal increased even two orders of magnitude. The reduction of full-width at-half-maximum (FWHM) and the increase of the intensity of X-ray rocking curve indicated an improvement of the crystal quality. PL measurements also showed the crystal quality improved after annealing. No characteristic peak of 241Am γ-ray could be observed in the detector fabricated with as-grown crystal. Remarkably, for the detector fabricated with annealed crystals, the peak of 241Am γ-ray appeared. And the energy resolution and μτ value were improved as the annealing time increased. Specially, 120 h annealed CMT:In crystal with 10.11% energy resolution and 1.20×10−3 cm2/V μτ value has the best detector performance.

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 cm2. 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

References (23)

  • O.S. Babalola et al.

    J. Cryst. Growth

    (2009)
  • J. Parkin et al.

    Nucl. Instrum. Methods A

    (2007)
  • Y.Y. Du et al.

    J. Cryst. Growth

    (2012)
  • X.W. Zhang et al.

    J. Cryst. Growth

    (2009)
  • K.H. Kim et al.

    J. Cryst. Growth

    (2012)
  • G. Yang et al.

    J. Cryst. Growth

    (2013)
  • G. Piacentini et al.

    J. Cryst. Growth

    (2015)
  • J.J. Zhang et al.

    J. Cryst. Growth

    (2012)
  • S.U. Egarievwe et al.

    Nucl. Instrum. Methods A

    (2015)
  • K.P. Reddy et al.

    J. Mater. Sci. Lett.

    (2002)
  • K.H. Kim et al.

    J. Appl. Phys.

    (2009)
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