The Study of Epitaxy with Spot Profile Analysis of LEED (SPA-LEED)

Abstract

The growth of single crystalline layers on single crystalline substrates (epitaxy) has proven to be a powerful method of producing well controlled layers down to a thickness of one atomic layer. Usually, however, the “success” of epitaxy is checked with fairly thick layers (of > 10 – 100 nm), since only then the quality may be tested with usual x-ray techniques in air or after preparation (cross section or removal from substrate) with TEM. The study of thin epitaxial layers down to monolayers requires both a perfect substrate and well defined deposition techniques, which is best provided with clean, annealed surfaces in uhv and molecular beam deposition. Additionally a structural technique is needed in situ with surface sensitivity and atomic resolution. Several recent microscopy techniques may be used like transmission or reflection electron microscopy /1/, low energy electron microscopy /2/ and scanning tunnel microscopy /3, 4/. All imaging techniques have the advantage of an easy qualitative evaluation of the kind and shape of any deviations from a perfect surface. It is, however, difficult to obtain quantitative informations as on average sizes or probability distributions, since here an enormous amount of images would be required. For that purpose diffraction techniques are better suited, since they providea perfect average and exact values on distributions from start on /5, 6, 7, 8/. Although many diffraction techniques are in use (reflection high energy electron diffraction /9, 10/, atom diffraction /11, 12/, x-ray diffraction /13/), here only low energy electron diffraction is considered, since it has so far provided the most quantitative results.