Ab initio studies of S chemisorption on GaAs(100)

Abstract

Ab initio molecular orbital calculations are used to study S chemisorption on reconstructed GaAs(100) surfaces. Three cluster models are developed to simulate the main characteristics of 4×2, 4×6, and 2×6 reconstructed GaAs(100) surfaces. S atoms chemisorb preferentially on bridge sites and dramatically change the surface geometry. If a single S is adsorbed on a bridge site by breaking a Ga—Ga dimer bond, the Ga–Ga separation increases to 4.10 Å (from the dimerized separation of 2.80 Å), with a concomitant lowering of the bond energy by 0.07 (hartree). When two S atoms are adsorbed on adjacent bridge sites, the two S atoms weakly repel each other (establishing themselves ∼10° off from the normal bridge position). At the equilibrium geometry, each S atom retains a charge of −0.6 (e) and increases the net dipole moment perpendicular to the surface by −1.12 (hartree). This dipole moment in turn drives holes (electrons) toward (away) from the surface and increases the photoluminescence efficiency. Calculated electronic structure and local density of states also reflect a large charge accumulation near adsorbed S atoms.

Surface Chemistry of Prototypical Bulk II−VI and III−V Semiconductors and Implications for Chemical Sensing

“…Defects owing to surface reconstruction are also termed intrinsic. Theoretical studies suggest that by occupying vacant coordination sites of surface atoms, adsorbates can induce surface atoms to adopt near-bulk coordination geometries; in some cases, this may even lead to removal of intrinsic surface states. − In contrast, extrinsic surface states are new states introduced by foreign adsorbed material. These new states correspond to dangling bonds of the adsorbate, which energetically may lie within the band gap or overlap with continuum bulk states.…”

First-principles study of GaAs(001)-β2(2×4) surface oxidation and passivation with H, Cl, S, F, and GaO

“…The origin of Ga 2 O 3 passivation mechanisms for reconstructed GaAs͑001͒ surface was investigated by using Ga 7 As 7 O 2 H 20 cluster model. 15 The simulation showed that the reduction in the density of surface states located within the bulk energy gap derives from initial near-bridgebonded O atoms. However, this cluster models could overestimate energy gap due to the strong quantum size effect of GaAs material.…”

A cluster study of aluminum adsorption on Ga-rich GaAs(100)(2 × 1) and β (4 × 2) surfaces

“…Different sizes of clusters are used to represent the same surface because of non-uniqueness of a specific cluster to represent a surface and also to study dependence and convergence of cluster properties with respect to cluster sizes. As a comparison, Guo-Ping and Ruda [29] used a surface Ga-Ga dimer bond length of 2.80 Å in a similar ab initio cluster study of the adsorption of sulfur on the Ga-rich GaAs(100) surface. They used a Ga 7 As 7 H 20 cluster to represent the (4 × 2), (4 × 6), and (2 × 6) surfaces and found that S atoms chemisorbed preferentially on bridge sites.…”