A Leed Investigation of (111) Oriented Si, Ge and GaAs Surfaces Following Pulsed Laser Irradiation
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Gibbons, Hess, and Sigmon, eds. Laser and Electron-Beam Solid Interactions and Yaterials Processing
A LEED INVESTIGATION OF (111) PULSED LASER IRRADIATION*
ORIENTED Si,
Ge AND GaAs SURFACES FOLLOWING
D. M. ZEHNER, J. R. NOONAN, H. L. DAVIS, C. W. WHITE AND G. W. OWNBY Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
ABSTRACT The low energy electron diffraction (LEED) patterns obtained from clean (111) oriented Si, Ge and GaAs single crystals subsequent to their irradiation with the output of a pulsed ruby laser in an ultra-high vacuum (UHV) environment suggest that metastable (lxl) surface structures are produced in the regrowth process. Conventional LEED analyses of the Si and Ge surfaces suggest that they terminate in registry with the bulk but that the two outermost interlayer spacings differ from those of the bulk. For the case of Si these changes are a contraction of 25.5 ± 2.5% and an expansion of 3.2 ± 1.5% between the first and second and second and third layers respectively.
INTRODUCTION The results of recent experiments in which single crystal semiconductors are irradiated with the output of a laser in an ultra-high vacuum (UHV) environment demonstrate that the epitaxial regrowth process extends to the outermost surface layers and that clean, well-defined surface structures are produced [1-4]. In particular, the low energy electron diffraction (LEED) spot patterns obtained from surfaces of Si [4-6] and Ge [5](111) oriented single crystals indicate that metastable (Ixl) structures can be produced with this process. These observations are to be contrasted with the reconstructed surface arrangements present after a standard in situ prenaration technique (cleavage or sputtering followed by thermal annealing). Although extensively investigated [7], the successes achieved in the structural determinations of the reconstructed surfaces have been quite limited. Thus a previous investigation aimed at determining the geometric structure in the outermost layers of Si(]11) attempted to avoid the difficulties arising from the reconstruction by using impurities (-5% of a monolayer of Te) to stabilize a (lxl) structure and a conventional LEED analysis was performed [8]. However, it is difficult to assess the effects due to the presence of impurities and thus compare results of this investigation with predictions of various model calculations. Since the (ixl) surface structures obtained by laser irradiation are also observed to be atomically clean [1], we have initiated detailed LEED analyses of these surfaces. Results for the Si(lll) surface suggest a bulklike layer termination exhibiting no ordered lateral reconstruction with first to second and second to third interlayer spacings contracted by 25.5 ± 2.5% and expanded by 3.2 ± 1.5% with respect to bulk values. Initial results for the Ge~lil) surface show similar types of relaxations. While (lxi) spot patterns are obtained from both the (Ill) and (iii) surfaces of GaAs, the loss of As from the selvedge region and the presence of nons
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