The GaAs(001)-(2 × 4) Surface:  Structure, Chemistry, and Adsorbates

Abstract

A series of ab initio simulations, based on density functional theory, of the structure of the clean GaAs-(001)-(2 × 4) surface and of C 2 H 2 , C 2 H 4 , and trimethylgallium (TMGa) adsorbates are described. This surface was selected because of its importance in the growth of GaAs by molecular beam epitaxy. After summarizing briefly the theoretical basis of the computational methods used in the paper, we review critically what is known from experiment and theory about the structure of the clean surface. We argue that there is now strong evidence in favor of the "trench dimer" model for the -phase of the clean surface, while the structures of the R and γ phases are less settled. We then present ab initio simulations of the trench dimer, the three dimer, and the gallium rebonded models of the clean GaAs(001)-(2 × 4) surface and discuss their common structural and bonding features. Ab initio simulations of C 2 H 2 and C 2 H 4 adsorbates at arsenic dimers of the GaAs(001)-(2 × 4) surface are then presented. The changes in the bonding configurations of both the adsorbates and the surface arsenic dimers are explained in terms of changes in the bond orders and local hybridization states. The As dimer bond is broken in the stable chemisorbed states of the molecules. However, an intermediate state, in which the As dimer is still intact, provides a significant barrier to chemisorption in both cases. This barrier, and its absence at the Si(001) surface, stems from the two extra electrons in the As dimer compared with the Si dimer. We then go on to describe the results of 14 ab initio simulations of structures connected with the chemisorption and decomposition of TMGa on the GaAs(001)-(2 × 4) surface. TMGa is commonly used in the growth of GaAs crystals from the vapor phase. The results of these simulations are used to explain a number of experimental observations concerning the surface coverage and the decomposition of TMGa to dimethylgallium and monomethylgallium. Significant technical aspects of the calculations, notably the number of relaxed layers in the slab calculations and the necessity to use gradient-corrected adsorption energies, are stressed. The paper also contains critical comments about ab initio simulations of the GaAs-(001)-(2 × 4) clean surface and about the model based on a "linear combination of structural motifs".

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

“…[3][4][5] It consists of alternating planes of Ga and As that are separated by 1.41 Å. 5 Both Ga-terminated and As-terminated GaAs͑001͒ surfaces were observed to reconstruct forming As-As dimers or Ga-Ga dimers on the surface.…”

Metalorganic chemical-vapour-deposition (MOCVD) of InGaAs, BGaAs, and BInGaAs: Quantum chemical calculations on the mechanisms

“…However, little is known about intermediate structures at the surface during the MOCVD growth processes as the structures of steps and kinks with chemisorbed gas-phase species. Experimental and theoretical studies provide some general facts on the reaction mechanisms during the MOVCD at the GaAs(0 0 1) surface, especially by TMG and arsine precursors [28][29][30][31][32][33]: TMG is being dissociatively chemisorbed at arsenic dimers, followed by methyl desorption from gallium surface species. The remaining gallium atoms form dimers.…”

“…Jenichen, C. Engler / Journal of Crystal Growth 304 (2007)[26][27][28][29][30][31][32][33][34][35][36] …”

A computational study of gas-phase and surface reactions in deposition and etching of GaAs and AlAs in the presence of HCl

“…As a result, the mechanism of growth from Ga(CH 3 ) 3 and AsH 3 is now largely understood [11][12][13][14]. At conventional growth temperatures (800-1000 C) the GaAs surface exhibits As-rich c(4 Â 4) reconstruction [15].…”