* Corresponding author. Tel.: #44 1865 273714; fax: 44 1865 273764; e-mail: zbigniew.mitura@materials.ox.ac.uk. Journal of Crystal Growth 198/199 (1999) 905—910 Interpretation of reflection high-energy electron diffraction oscillation phase Z. Mitura*, S.L. Dudarev, M.J. Whelan  Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK  Institute of Physics, Marie Curie-Sk!odowska University, pl. M. Curie-Sk!odowskiej 1, 20-031 Lublin, Poland Abstract The use of reflection high energy electron diffraction (RHEED) became very popular after the discovery of reflected electron beam intensity oscillations in the early 1980s. Although a number of theoretical explanations of the effect have already been given, many aspects of the question as to why RHEED oscillations appear still remains open. We propose a new mechanism which may lead to the appearance of RHEED oscillations. This mechanism can be briefly described as the periodic variation of diffraction peak positions due to changes in the average scattering potential near the crystal surface during the deposition of a new layer. We conclude that in a general case one can explain qualitatively the origin of RHEED oscillations as the superposition of effects due to: (1) periodic variations in surface roughness, (2) changes in interference conditions for waves scattered from different surface terraces and (3) periodic variations in the average potential in the topmost layer.  1999 Elsevier Science B.V. All rights reserved. PACS: 61.14.Hg; 68.35.Bs; 68.55.Jk Keywords: RHEED; Oscillations; MBE From early 1980s the use of reflection high en- ergy electron diffraction (RHEED) to monitor epi- taxial growth of thin films has become very popular [1]. This is largely a consequence of the discovery RHEED intensity oscillations [2,19,20]. It was ex- perimentally found that if epitaxial growth follows a layer-by-layer mode then regular oscillating cha- nges in the intensity of specularly reflected beam occur and the period of such oscillations corres- ponds to the deposition of one monolayer. How- ever, it has turned out that the theoretical explanation of this effect is not quite so simple. This is because a fully quantitative description of elec- tron diffraction from crystals can be achieved only if dynamical diffraction theory is employed. In fact, even for the case of perfectly flat surfaces, dynam- ical theoretical analysis is rather complicated. The case of a growing surface is far more difficult to deal with. Due to permanent theoretical progress in this research area, we may expect that some day we will 0022-0248/99/$ — see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 9 8 ) 0 1 0 4 0 - 9