Iso-electronic Sb impurities in GaAs studied by cross-sectional scanning tunneling microscopy

Abstract

Highly mismatched III/V alloys, such as GaAsN and GaAsSb, are known to suffer from segregation and clustering effects, which often limit their application in devices. In this cross-sectional scanning tunneling microscopy (X-STM) study, we explore the atomic-scale behavior of iso-electronic Sb doping atoms in MBE-grown dilute GaAs1-xSbx (0.01 < x < 0.03). We found that Sb atoms up to four layers below the cleavage surface can be identified in filled-state X-STM images. They appear with diverse anisotropic contrasts, depending on the depth of the Sb atom. These features are classified and are related to their depth below the cleavage surface through careful symmetry considerations. We show that the depth-dependent contrast of Sb atoms in filled-state imaging is determined by both topographic effects (lattice deformation due to the large Sb atom) and electronic effects (resonances of Sb atoms in the valence band). This study shows that in MBE-grown GaAsSb alloys, the Sb atoms can be rapidly incorporated, in which case the GaAsSb layers suffer little from segregation and sharp interfaces can be obtained. Additionally, short-range ordering of Sb, which can be uniquely studied by X-STM, has been analyzed in terms of nearest-neighbor-pair formation, and we find that in MBE-grown GaAsSb materials, a tendency to form Sb pairs or clusters can be suppressed. This opens the route to create high-quality devices based on the highly mismatched GaAsSb alloy.