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We have determined the structure of AlSb and GaSb (001) surfaces prepared by molecular beam epitaxy under typical Sb-rich device growth conditions. Within the range of flux and temperature where the diffraction pattern is nominally ͑1 3 3͒, we find that there are actually three distinct, stable ͑4 3 3͒ surface reconstructions. The three structures differ from any previously proposed for these growth conditions, with two of the reconstructions incorporating mixed III-V dimers within the Sb surface layer. These heterodimers appear to play an important role in island nucleation and growth. PACS numbers: 68.35.Bs, 61.16.Ch, 73.61.Ey, 81.15.Hi The surface reconstruction on a semiconducting material is the starting point for understanding the mechanisms of growth from the vapor. The steric and energetic landscape of the surface reconstruction determines the kinetic factors for adsorption, diffusion, and desorption, and provides the template for island nucleation [1]. These factors are critical to our understanding of growth and the formation of interfaces between materials, particularly for the case of III-V semiconductor quantum heterostructures, which are key components in a wide range of optical and high frequency electronic devices under development. Many of the most promising applications require extremely thin layers, so that even submonolayer variations in film thickness and interfacial roughness can dramatically affect the ultimate device performance [2,3]. To achieve the level of morphological control needed to reproducibly fabricate optimized III-V devices, a detailed understanding of the relevant surface reconstructions and the mechanisms by which epitaxy proceeds is essential.The structure of III-As and III-P (001) surfaces under typical device growth conditions (V͞III flux . 1) has been generally established [4,5]. For the much-studied case of GaAs, the extensive experimental and theoretical knowledge accumulated about the surface structure has led to significant progress in understanding the atomistic mechanisms of growth during molecular beam epitaxy (MBE) [6,7]. In contrast, the III-Sb device surfaces are poorly understood, despite their demonstrated potential for a variety of advanced electronic and optoelectronic applications [8]. Although the surface structures have been determined for atypical, extreme Sb-rich conditions-InSb and AlSb have the c͑4 3 4͒ structure common to the arsenides, and GaSb reconstructs into unusual, metallic ͑n 3 5͒ structures [9,10]-even after more than 20 years of study [11], the atomic-scale structures under more typical growth conditions have yet to be resolved. During device growth both GaSb and AlSb usually exhibit a ͑1 3 3͒-like reflection high-energy electron diffraction (RHEED) pattern, with the GaSb RHEED further delineated into distinct c͑2 3 6͒ and ͑1 3 3͒ (higher temperature/lower Sb flux) regimes [12,13]. Simple Sb-dimer row models for these reconstructions have been proposed [13,14], but scanning tunneling microscopy (STM) studies of the III-Sb(001) surfaces...

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We have used cross-sectional scanning tunneling microscopy and x-ray diffraction to characterize and compare the effects of As2 versus As4 on the growth of InAs/GaSb heterostructures by molecular beam epitaxy. When GaSb surfaces are exposed to an As2 flux, the As exchanges with the surface Sb in an anion exchange reaction that creates layers of GaAs. In contrast, when GaSb surfaces are exposed to As4 fluxes, there is no evidence of the As-for-Sb exchange reaction. When comparing the use of As2 and As4 in periodic InAs/GaSb superlattices, the differences in the As incorporation rate into GaSb is further evident in x-ray diffraction spectra as a shift in the average lattice constant of the epilayer due to GaAs bond formation. Although inhibiting the exchange reaction would be useful in the minimization of the cross incorporation of As in the GaSb layers, the growth of InAs/GaSb heterostructures using As4 can be complicated by the introduction of film instabilities that have not been observed in growths using As2.

We describe a lattice of InAs nanowires that spontaneously organizes in three dimensions within an InAs/GaSb superlattice grown under high As 4 flux. As characterized by x-ray diffraction and cross-sectional scanning tunneling microscopy, the periodic nanowires are ~10 nm high, 120 nm wide, and many microns long along [110], with face-centered cubic-like vertical ordering within the superlattice. The unusual vertical ordering creates a lateral composition modulation with half the period of the nanowires. The structure appears to arise from the InAs misfit stress combined with specific InAs and GaSb growth kinetic effects.