Ab-Initio Studies of AlSb (001) Adatom Behavior and Reconstruction
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ABSTRACT We discuss a recent investigation of adatom behavior on the AlSb(001) surface using first-principles electronic structure methods based on the density functional theory. For Al and Sb adatoms, we find a number of novel adatom structures that differ dramatically from previous results for the superficially similar group-III arsenides. In particular, we conclude that it is energetically favorable for an Al adatom to incorporate substitutionally into the outermost layer of the AlSb surface. This observation helps motivate a proposed new reconstruction for the AlSb(001) surface. Finally, we argue that the unusual adatom behavior identified for this surface probably results from the presence of a dimer row composed of a double layer of group-V atoms in the reconstruction, and therefore, it should be generic to all of the antimonides, as well as, the c(4 x 4) reconstruction of the arsenides and phosphides. INTRODUCTION Epitaxial growth of zincblende III-V semiconductors is the cornerstone of such important technologies as wireless and optical communications and solid state lasers, light emitting diodes, and optical sensors. The nearly lattice matched "6.1 A family" consisting of InAs, GaSb, and AtSb shows particular promise for use in high speed electronic and optoelectronic devices. Since such devices typically involve very thin AlSb barrier layers, there is considerable interest in controlling the surface roughness and interface morphology of epitaxially grown AlSb. This requires understanding and controlling the epitaxial growth process. During the epitaxial growth of III-V semiconductors by molecular beam epitaxy (MBE), group-III atoms and group-V molecules (dimers or tetramers) impinge on the surface. The group-V species usually stays on the surface for only a short time before returning to the vacuum. In contrast, the group-III species typically sticks and diffuses across the surface. Therefore, it can be argued that the diffusion of group-III adatoms is the principle process controlling MBE growth. Furthermore, understanding the behavior of group-Ill adatoms is a crucial building block for understanding other growth processes such as island nucleation and step edge attachment. For these reasons, the focus of this paper is an investigation of the behavior of Al adatoms on the AlSb(001) surface using theoretical techniques based on the Kohn-Sham Density Functional Theory. We will argue that the behavior of Sb adatoms helps determine the behavior of Al adatoms, and therefore it will also be discussed. The remainder of the paper is organized as follows: First, we give the background to the present calculations including the experimentally motivated surface reconstruction that we have assumed to be the clean surface. Then, we report details of our method, which are followed by our actual results for the adatom behavior. Finally, we discuss the implications of our method for the stability of our assumed surface reconstruction, and we argue that our results should be generally applicable to a variety of other III
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