Electronic Properties of (100) Surfaces of GaSb and InAs and Their Alloys with GaAs
by R. Ludeke
Smooth, monocrystalline (100) surfaces of the alloys In1−xGaxAs and GaSb1−y Asy were prepared by molecular beam epitaxy. Both As-stabilized c(2 × 8) and metal-stabilized c(8 × 2) surface reconstructions were observed for In1−xGaxAs over the entire alloy range. GaSb1−yAsy exhibited a c(2 × 6) or (2 × 3) structure for y ≲ 0.2, and, after a transition region, the anion-stabilized c(2 × 8) or the Ga-stabilized c(8 × 2) structures for y ≳ 0.5. Electron energy loss spectroscopy revealed the simultaneous presence of two empty, dangling-bond derived surface states in both alloy systems. For In1−xGaxAs the In-derived empty surface state lies ≈0.4–0.5 eV below that of Ga and moves from above the conduction band edge into the band gap for x ≳ 0.6. The overlap between the Ga-and In-derived empty surface states causes the quenching of the Ga(3d) surface exciton. For GaSb1−yAsy the Sb dangling bonds generate an empty, localized surface state which lies 0.2–0.3 eV above the empty, Ga-derived surface state. Both levels lie above the conduction band edge throughout the alloy range.