Spontaneous Formation of Surface Antisite Defects in the Stabilization of the Sb-Rich GaSb(001) Surface

This Letter solves the long-standing puzzle [Phys. Rev. Lett. 79, 693 (1997)] of why GaSb(001) apparently violates the electron counting rule (ECR) in forming a reconstruction featuring long Sb-dimer chains, rather than the c(4×4) reconstruction found in all other arsenide and antimonide III V compounds in the V-rich regime. We find that an alternative strategy, that in fact satisfies the ECR, is followed by the Sb-rich GaSb(001) surface, whereby long Sb-dimer chains are stabilized by randomly distributed subsurface Ga antisite defects. The excess of surface Sb drives the defect formation that in turn stabilizes the surface in a metastable phase. The transition to the c(4×4) reconstruction, where the ECR is instead satisfied through missing dimers, is therefore inhibited. Our conclusions are supported by ab initio simulations of experimental reflectance anisotropy spectra.