The effects of the magnitude and direction of biaxial compressive strain on the formation and migration barrier of a neutral vacancy in germanium were studied using density functional theory. Bulk Ge cells with (100) and (111) planes under various in-plane biaxial compressive strains were investigated to model epitaxial Ge on Si1-xGex substrate. Biaxial compressive strain decreased the vacancy formation energy by 68% and 81% for the (100) and (111) super-cells, respectively, when Ge was assumed to be epitaxially grown on Si. The biaxial compressive strain hardly affected the migration behaviour of a vacancy in the (100) super-cell. On the contrary, in the (111) super-cell, the migration barrier energy showed anisotropic behaviour; the migration along the perpendicular and virtually parallel directions with respect to the strain became distinctly more difficult and slightly easier, respectively. The effects of strain on the formation and migration of the vacancy were explained by the atomic relaxation around it and electron redistribution. By comparing the formation energy and migration barrier energy, vacancy formation was suggested to be dominant for vacancy-mediated diffusion in Ge.

Effects of Magnitude and Direction of the Biaxial Compressive Strain on the Formation and Migration of a Vacancy in Ge by using Density Functional Theory. J.Lee, K.D.Na, S.C.Lee, C.S.Hwang, J.H.Choi: Journal of Applied Physics, 2011, 110[3], 033504