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We present a cross-section scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and ab initio density-functional theory simulations study of the cleaved nonpolar (1 1̄ 00) surface (m -plane) of n -type HVPE GaN free-standing quasisubstrates. Atomically resolved empty and filled states STM topographies show that no reconstruction occurs upon cleavage, as predicted by theory. STS measurements on clean and atomically flat cleaved surfaces (defect concentration σd ≤2× 1012 cm-2) show that the Fermi energy is not pinned and the tunneling current flows through Ga-like electronic states lying outside the fundamental band gap. On surface areas with defect concentration σd 3× 1013 cm-2, the Fermi energy is pinned inside the band gap in defect-derived surface states and tunneling through filled (empty) N-like (Ga-like) states takes place. © 2009 The American Physical Society.

We present a combined cross-section scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) and ab initio simulations study of the nonpolar (11 2̄ 0) cleaved surface of 6H-SiC. The experimental results show an unreconstructed surface in agreement with theory. Upon truncation, two surface bands appear inside the semiconductor band gap: one empty band localized on the Si atoms and one filled band on the C atoms. According to the STS experimental results on n -doped samples, the Fermi energy is pinned at the surface inside the band gap. By comparison of STM filled and empty states topographies we propose that on the fresh cleaved surface the Fermi level lies at the bottom of the Si-like band. The calculated STM images reproduce the experimental contrast of the 6H stacking sequence and its bias dependence very well. © 2007 The American Physical Society.

We performed ab initio calculations to identify and characterize the stationary points of the potential energy surface experienced by a C adatom deposited on the root 3- x root 3 beta-SiC(111) surface. A kinetic Monte Carlo simulation relying on the ab initio calculated parameters allowed us to follow C diffusion at realistic temperature and time scales. We found that the C diffusion occurs mostly around the Si adatoms characteristic of the root 3- x root 3- reconstruction.

In this paper we present a first-principle study on the energetics of a single As2 molecule on GaSb(0 0 1) reconstructed surface. In order to shed light into the mechanisms of anion exchange at the Sb-rich GaSb(0 0 1) surface, we studied firstly As2 adsorption and then As for Sb exchange. We identify a surface region where both the processes are energetically favored. The results of this twofold analysis can be combined to derive possible reaction paths for the anion exchange process. © 2005 Elsevier B.V. All rights reserved.

We report results of ab initio total-energy and electronic-structure calculations for the Sb-stabilizedGaSbs001d surface. We consider different reconstruction models proposed in the literature on the basis ofexperimental observations in typical GaSb growth conditions and present the T=0 surface stability diagram.We found that dimer-baseds433d reconstructions are favored over widely proposed s133d/cs236d modelsthat have a similar structure, but do not satisfy the electron counting rule. We discuss also the stability of theb2s234d reconstruction for comparison with the As-based GaAss001d and InAss001d surfaces that present thisphase in a wide range of surface preparation conditions. We predict the surface band structure of the GaSbs001dstable configurations and identify the nature of the surface bands. All thes433d reconstructions turned out tobe semiconducting with an energy gap slightly smaller than the GaSb bulk value.DOI: 10.1103/PhysRevB.71.075323 PACS numberssd: 68.35.Md, 71.15.MbI. INTRODUCTION

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}\mathrm{S}\mathrm{i}\mathrm{C}(111)\mathrm{\text{\ensuremath{-}}}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.

We present the ab initio results for the energetics of several SiC surfaces having different underlying bulk polytypes, to investigate the role of surface effects in the mechanisms of stacking inversion in SiC. We considered the Si adatom $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ reconstruction for the cubic SiC(111) and the hexagonal SiC(0001) surfaces, taking into account the different subsurface bulk terminations compatible with the $4H$ and $6H$ polytypes, and allowing for two opposite stacking orientations of the topmost surface layer. Our investigation reveals that the energy differences among SiC polytypes are enhanced at the surface with respect to the bulk, and two-dimensional effects favor the formation of cubic SiC. We discuss the relevant role played by the surface energetics in the homoepitaxial growth of SiC.