Elsevier

Applied Surface Science

Volume 253, Issue 20, 15 August 2007, Pages 8470-8473
Applied Surface Science

Dependence of the microstructural properties on the substrate temperature in strained CdTe (1 0 0)/GaAs (1 0 0) heterostructures

https://doi.org/10.1016/j.apsusc.2007.04.019Get rights and content

Abstract

CdTe thin films were grown on GaAs (1 0 0) substrates by using molecular beam epitaxy at various temperatures. The bright-field transmission electron microscopy (TEM) images and the high-resolution TEM (HRTEM) images showed that the crystallinity of CdTe epilayers grown on GaAs substrates was improved by increasing the substrate temperature. The result of selected-area electron diffraction pattern (SADP) showed that the orientation of the grown CdTe thin films was the (1 0 0) orientation. The lattice constant the strain, and the stress of the CdTe thin film grown on the GaAs substrate were determined from the SADP result. Based on the SADP and HRTEM results, a possible atomic arrangement for the CdTe/GaAs heterostructure is presented.

Introduction

The growth of high-quality CdTe thin films has attracted much interest because of their applications in the areas of solar energy conversion, gamma-ray detection, and electro-optic modulation due to their low thermal noise and large absorption coefficient [1], [2], [3], [4], [5]. CdTe epitaxial layers have been extensively grown because CdTe thin films can be useful buffer layers for the growth of Hg1−xCdxTe epilayers [6], [7], [8]. However, since the growth of high-quality CdTe/GaAs heterostructures has inherent problems due to the large lattice mismatch (Δa/a = 12.77% at 25 °C), studies of the microstructural properties of CdTe/GaAs heterostructures are very important for achieving high-quality optoelectronic devices that can operate in the near-infrared region of the spectrum [9]. In addition, studies of the improvement on the microstructural properties play a very important role in enhancing device efficiency [10], and systematic studies concerning the microstructural properties of the CdTe/GaAs heterostructures dependent on the substrate temperature are still necessary if high-quality heterostructures are to be obtained. Even though some studies concerning the orientation of the CdTe epitaxial films grown on GaAs (1 0 0) substrates dependent on the preheating temperature have been reported [11], [12], [13], [14], [15], very few works on the dependence of the microstructural properties on the substrate temperature for CdTe thin films grown on GaAs (1 0 0) substrates have been performed [16].

This paper reports the dependence of the microstructural properties on the substrate temperature of CdTe epitaxial films grown on GaAs (1 0 0) substrates by using molecular beam epitaxy (MBE) at various temperatures. Transmission electron microscopy (TEM) and selected-area electron diffraction pattern (SADP) measurements were performed to investigate the microstructural properties of the CdTe thin films grown on GaAs (1 0 0) substrates. A possible crystal for the CdTe/GaAs heterostructure is presented on the basis of the high-resolution TEM (HRTEM) and the SADP results.

Section snippets

Experimental details

Elemental Cd and Te with purities of 99.9999% were used as the source materials and were precleaned by repeated sublimation. Si-doped N-type (1 0 0) GaAs substrates were degreased in trichloroethylene (TCE), etched in acetone, etched in a Br-methanol solution, and rinsed in de-ionized water thoroughly. As soon as the chemical cleaning process was finished, the GaAs substrates were mounted onto a molybdenum susceptor. Prior to CdTe thin-film growth, the GaAs substrates were thermally cleaned at 600

Results and discussion

Fig. 1 shows cross-sectional bright-field TEM images of the CdTe/GaAs heterostructures grown at various growth temperatures of (a) 300, (b) 310, (c) 320, and (d) 340 °C. The bright-field TEM images depict the top CdTe thin film and the bottom GaAs substrates. The dislocations in the CdTe thin films appears as lines in the images of the CdTe films, as shown in Fig. 1. The defects, such as dislocations, in the CdTe thin films decrease with increasing substrate temperature, indicative of the

Summary and conclusions

The TEM images showed that the crystallinity of the CdTe epitaxial films grown on the GaAs (1 0 0) substrates was improved with increasing substrate temperature due to the thermal effect. The lattice constant and the horizontal stress of the CdTe thin film were determined from the SADP results, and a possible schematic diagram of the crystal structure for the CdTe/GaAs heterostructure was proposed on the basis of the SADP and HRTEM results. These observations can help improve understanding of the

Acknowledgement

This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2004-005-D00166).

References (16)

  • J.P. Faurie et al.

    Mater. Sci. Eng., B

    (1993)
  • S.K. Pandey et al.

    Thin Solid Films

    (2005)
  • A. Million et al.

    J. Cryst. Growth

    (1996)
  • Y.B. Hou et al.

    Appl. Surf. Sci.

    (1999)
  • N.V. Sochinskii et al.

    Thin Solid Films

    (2001)
  • H.S. Lee et al.

    J. Cryst. Growth

    (2006)
  • Y.P. Chen et al.

    J. Electron. Mater.

    (1993)
  • Y.S. Ryu et al.

    J. Mater. Res.

    (2003)
There are more references available in the full text version of this article.

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