First principles analysis on the stability of C, Sn atoms near the surface of Ge thin film

Abstract

To apply the germanium (Ge) thin film for various electronic devices, energy band structure should be controlled by carbon (C) and/or Tin (Sn) doping. It is important to understand the stable atomic configurations of C and Sn atoms near the (001) surface of a Ge thin film. In this study, first principles calculation based on density functional theory was performed to obtain the formation energies and the thermal equilibrium concentrations of C and Sn atoms near the surface of Ge thin film. The results of the analysis are threefold. First, C and Sn atoms are most stable at the first atomic layer of the Ge thin film, and the surface does not affect the stability of C or Sn atoms deeper than the fifth layer. Second, C and Sn atoms at the second to fourth layer increase the thermal equilibrium concentration of newly arrived C and Sn atoms at the surface during film growth. Third, in the case of mono-doping, formation energy of C (Sn) at the (001) surface increases with increasing concentration of surface C (Sn). In the case of co-doping at C/Sn concentration ratio of 1:1, the increases of formation energies are suppressed in comparison to the case of mono-doping. It is concluded from these results that co-doping enhances the incorporation of C and Sn atoms in the Ge thin film. Furthermore, the doped atom near Si surface becomes more stable than that in the Si bulk, and it is more remarkable in comparison to Ge.

Keywords

• ge
• si
• thin film
• atomic configuration
• first principles calculation