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 $c(4\times 4)$ 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 $c(4\times 4)$ 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.

Figure 1

(a)–(c) Ball-and-stick models of V-rich III–V(001) reconstructions (top view, unless specified otherwise). Panel (d) shows extended cells (axes rotated by 90°) containing long dimer chains, closely spaced [($8\times 2$)] or separated by in-dimers [($8\times 3$)]. Shaded regions define primitive surface unit cells.

Figure 2

Surface phase diagram for GaSb(001). Surface energies $\gamma$ are plotted relative to the $\alpha (4\times 3)$ reconstruction.

Figure 3

(a) Surface Ga antisite defect formation energy (DFE) as a function of the number of excess electrons $\nu$. Points marked $c(2\times 10)\mathrm{\text{−}}s1a$ and $c(2\times 6)\mathrm{\text{−}}s*$ indicate the average defect energies of these structures. The numbers in parenthesis indicate dimers removed from initial extended cells. (b) Surface energies of GaSb and GaAs(001) metallic chains, compared with those of chains modified to obey the ECR by means of removal of dimers or addition of defects.

Figure 4

Reflectance anisotropy spectra of GaSb(001). Top: calculated spectra, with and without Ga antisites. Bottom: experimental spectra, taken from Refs. 14 (a) and 12 (b).