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Title: Molecular beam epitaxy growth of high quality p-doped SnS van der Waals epitaxy on a graphene buffer layer
Authors: Wang, W
Leung, KK
Fong, WKP
Wang, SF
Hui, YY
Lau, SP 
Chen, Z
Shi, LJ
Cao, CB
Surya, C 
Issue Date: 1-May-2012
Source: Journal of applied physics, 1 May 2012, v. 111, no. 9, 093520, p. 1-8
Abstract: We report on the systematic investigation of optoelectronic properties of tin (IV) sulfide (SnS) van der Waals epitaxies (vdWEs) grown by molecular beam epitaxy (MBE) technique. Energy band simulation using commercial CASTEP code indicates that SnS has an indirect bandgap of size 0.982 eV. Furthermore, our simulation shows that elemental Cu can be used as a p-type dopant for the material. Growth of high quality SnS thin films is accomplished by MBE technique using graphene as the buffer layer. We observed significant reduction in the rocking curve FWHM over the existing published values. Crystallite size in the range of 2–3 μm is observed which is also significantly better than the existing results. Measurement of the absorption coefficient, α, is performed using a Hitachi U-4100 Spectrophotometer system which demonstrate large values of α of the order of 10⁴cm⁻¹. Sharp cutoff in the values of α, as a function of energy, is observed for the films grown using a graphene buffer layer indicating low concentration of localized states in the bandgap. Cu-doping is achieved by co-evaporation technique. It is demonstrated that the hole concentration of the films can be controlled between 10¹⁶ cm⁻³ and 5 × 10¹⁷cm⁻³ by varying the temperature of the Cu K-cell. Hole mobility as high as 81 cm²2V⁻¹s⁻¹ is observed for SnS films on graphene/GaAs(100) substrates. The improvements in the physical properties of the films are attributed to the unique layered structure and chemically saturated bonds at the surface for both SnS and the graphene buffer layer. Consequently, the interaction between the SnS thin films and the graphene buffer layer is dominated by van der Waals force and structural defects at the interface, such as dangling bonds or dislocations, are substantially reduced.
Keywords: Band structure
Dangling bounds
Energy gap
Hole mobility
IV-VI semiconductors
Localised states
Molecular beam epitaxial growth
Semiconductor epitaxial layers
Semiconductor growth
Semiconductor thin films
Tin compounds
Ultraviolet spectra
Vacuum deposition
Van der Waals forces
Visible spectra
Publisher: American Institute of Physics
Journal: Journal of applied physics 
ISSN: 0021-8979
EISSN: 1089-7550
DOI: 10.1063/1.4709732
Rights: © 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in W. Wang et al., J. Appl. Phys. 111, 093520 (2012) and may be found at
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