THE EFECTS OF SUBSTRATE ORIENTATION ON THE GeMn FILM FORMATION

Abstract

In this paper, Reflection High- Energy Electron Diffraction (RHEED),  High Resolution Transmission Electronic Microscopy - HRTEM) along with the first-principles total energy calculations within density functional theory were used to ananlysis the effects of substrate orientation on the formation of GeMn films grown on Ge(001) and Ge(111) substrates. The samples were grown by mean of Molecular Beam Epitaxy (MBE) at T_S = 130^oC, Mn concentration ~ 6% and the thickness of ~ 80nm to ensure the formation of GeMn nanocolumns on the Ge(001) substrate. Due to the Mn atoms tend to float upward toward the new interstitial sites, Ge_0,94 Mn_0,06 film grown on Ge(001) substrate exhibits the nanocolumn structure along the growth direction. In contrast, for the Ge_0,94 Mn_0,06 film grown on Ge(111) substrate, Mn adatoms can easily  diffuse into deeper layers through the interstitial sites with relatively low energy barriers and resulted in the formation of Mn-rich streaks along a preferred direction [110]. The physical origin for the contrasting behavior of Mn along the two different orientations is tied to the different surface reconstructions.