Atomic Structure of the Sb-Stabilized GaAs(100)-(2×4) Surface

Abstract

The microscopic structure of the Sb stabilized GaAs(100)-(2 3 4) surfaces is investigated combining reflectance anisotropy spectroscopy with first-principles total energy minimization and tight-binding calculations of optical properties. We show that the model accepted so far, containing three Sb dimers in the outermost layer, is not a stable surface geometry. Our results reveal a coexistence of Sb and Ga dimers on the Sb-stabilized ͑2 3 4͒ surface. [S0031-9007(96)01679-1] PACS numbers: 68.35.Bs, 68.35.Md, 78.30.Fs, 78.66.Fd Understanding of the surface atomic structures and their modification through deposition of foreign atoms is crucial for both science and technology. In particular, the adsorption of group-V elements on (100) faces of III-V compound semiconductors is technologically important for the III-V heteroepitaxy [1]. Especially the adsorption of Sb on GaAs(100) has attracted interest due to the formation of an exceptionally abrupt interface [1,2] and the possible use of Sb as surfactant for metal growth on GaAs(100) [3,4]. Soft x-ray photoemission spectroscopy (SXPS), Auger electron spectroscopy (AES), and electron diffraction [LEED and reflection high-energy electron diffraction (RHEED), respectively] studies have shown that by Sb deposition on GaAs(100) and subsequent annealing a well-ordered ͑2 3 4͒ reconstruction is formed even at temperatures much higher than for the clean, As-terminated surface, due to stabilization by Sb dimers [1,5,6].Based on SXPS data and on the ͑2 3 4͒ RHEED pattern a first structural model for the Sb-induced reconstruction was suggested [1]. This model, based on three Sb dimers per surface unit cell, was constructed in analogy to the so-called GaAs(100)b͑2 3 4͒ structure, widely used in the past to describe As-terminated GaAs(100)-͑2 3 4͒ surfaces [7,8]. For the clean GaAs(100)-͑2 3 4͒ surface, however, recent experimental and theoretical studies have demonstrated that the equilibrium structure contains only two As dimers per unit cell in the topmost atomic layer, denoted as b2͑2 3 4͒ structure [9-12]. As shown in Ref. [9], the electrostatic interaction between the negatively charged surface As dimers destabilizes the three-dimer compared to the two-dimer structure. The same argument should hold if the As dimers are substituted by another group-V element like Sb, thus questioning the validity of the suggested structure for the Sb-stabilized ͑2 3 4͒ GaAs(100) surface. Meanwhile, x-ray standing wave (XSW) experiments [13] confirmed the existence of Sb dimers on the surface; however, conclusive results about the validity of the three-Sb-dimer model [1] were not obtained.The present study is aimed at the determination of the atomic structure of the Sb-stabilized GaAs(100)-͑2 3 4͒ surface, using a novel approach to investigate microscopic surface properties based on the surface optical response. We apply reflectance anisotropy spectroscopy (RAS), ab initio total-energy minimization (TE), and tightbinding (TB) calculations of optical properties to study the precise surface ge...

Surface modifications induced by bismuth on (001) GaAs surfaces

“…2 shows a comparison of an Sb terminated surface and a Bi-terminated surface at 450 C: Both Sb and Bi were deposited on a As-rich (2 Â 4) like surface. The Sb-terminated surface was prepared by exposure to 1 s of TMSb vapor (0.25 Pa) at 450 C: This surface has been observed in both UHV and OMVPE growth environments [12,13]. The Bi-terminated GaAs (0 0 1) surface was prepared by low TMBi exposure (1 s of TMBi at 0.7 Pa) at 450 C; corresponding to stage d in Fig.…”

Detection of surface states anisotropies at GaAs(001)(2 × 4) decapped surfaces

“…After the complete coverage of the substrate, besides a weak feature at 2.5 eV also visible on as-grown Sb-terminated GaAs(001) surfaces [37], the anisotropy mainly comes from the photon energy region close to the E 0 ′ bulk critical point. Near 4 eV (exactly at 3.9 eV) there is the characteristic plasmon loss of bulk silver [38].…”

In-situ monitoring, structural, and optical properties of ultrathin GaSb/GaAs quantum wells grown by OMVPE

“…The RDS spectrum under TMSb is very similar to the one reported for a GaAs surface capped with 2 ML of Sb, and annealed at 450∞C, which was correlated with a (3¥8)-like symmetry observed by low energy electron diffraction. 11 The (3¥8) surface was reported as an intermediate step, with annealing to higher temperature (500∞C) producing an Sb-stabilized (2¥4) reconstruction.…”