Analysis of GaSb and AlSb reconstructions on GaSb(111)A- andB-oriented surfaces by azimuthal-scan reflection high-energy electron diffraction

Abstract

The symmetry and existence ranges of GaSb and AlSb (111) A and B surface reconstructions are investigated using azimuthal-scan reflection high-energy electron diffraction (ARHEED) in a molecular-beam-epitaxy (MBE) environment. ARHEED patterns of all reconstructions within the accessible MBE group V flux-substrate temperature parameter field are presented and analyzed. The transition borders are mapped out as a reference for future growth experiments. The experimental results are interpreted on the basis of general construction principles for (111) surfaces of III-V semiconductors. ARHEED allows the complete determination of the two-dimensional in-plane reciprocal lattice in a single, continuous measurement. This allows the unambiguous identification of the reconstructions on (111) surfaces where the intrinsic symmetry is masked by the 120 • domain structure and possible disorder.

In Situ Observation of Epitaxial Li–Si-Nanostructure Formation on Si(111)

“…JCPDS # 04-004-4549) andLi 21 Si5 25 (JCPDS #04-007-0820) phase agrees sufficiently well. Since the diffraction peaks persisted and no additional ones were found, the final(post growth) XRD in-plane map (Figure 4) and out-of-plane (00L) scan (Figure 4) could be utilized to confirm the presence of both phases: The measured d spacings extracted from both agree well with the tabulated values for the Li 12 Si 7 and Li 21 Si 5 crystal structures as indicated by the numerical values in the corresponding figure captions.…”

“…In addition to crystal structure and epitaxial relation, the experimental results also allow conclusions about the underlying growth kinetics at substrate temperatures between 300 and 390°C: The initial Si substrates exposed to the Li flux converted initially to Li 12 Si 7 and later to Li 21 Si 5 crystallites which formed on the Si(111) substrate. The necessary Si had to originate from the surface where it reacted with the deposited Li.…”

“…Further information about the epitaxial relationship can be deduced from the XRD inplane map (Figure 4) where the {224}, {448}, and {6 6 12} peaks are aligned with the equivalent {224} peaks of the Si substrate. However, the in situ measurement shows also that for lower temperatures, the crystal grows polycrystalline by inplane rotations as indicated by the appearance of additional weaker Li 21 A close lattice match between two crystals enables the interface formation with low strain energy for pseudomorphic growth and consequently lower interface defect density. The lattices of materials with dissimilar crystal structures can be combined by matching multiples of their unit cells as closely as possible resulting in an enlarged in-plane interface unit cell.…”

“…The in situ XRD scan shown in Figure 2 indicates that first the Li 12 Si 7 crystals form. At lower temperatures additionally the Li 21 Si 5 phase forms. The appearance of the Li 21 Si 5 (111) surface symmetry (ARHEED Figure 3(a)) shows that its phase formation sets in at higher temperature and starts from the surface.…”

“…The observed orientation can be explained by formation of coincidence lattices between Si, Li 12 Si 7 , and Li 21 Si 5 . The (111) Li 21 Si 5 surface exhibits a approximately nine times larger (1 × 1) surface unit cell than the unreconstructed Si(111) surface. The kinetics of the nanostructure formation is influenced by both elements: The Si release mechanism from the crystalline substrate and its diffusion as well as the Li desorption and diffusion kinetics contribute.…”