Misfit evolution in the early stages of the heteroepitaxial growth of GaAs on Si(001): An in-situ X-ray scattering study

Abstract. We briefly describe, theoretical considerations in the quest to grow crystalline films with perfection in uniformity of thickness. The endeavor of perfect crystallinity is best served by growing epitaxially. Thickness uniformity is facilitated by growing in a monolayer-by-monolayer mode-so called Frank-van der Merwe (FM) mode. The island (Volmer-Weber ---VW) mode is undesirable; it promotes roughening and the creation of crystalline imperfections. Equilibrium criteria, proposed by Bauer, on the basis of shape equilibrium, predict that FM growth is favored by strong substrate bonding. The dependence of shape equilibration on adatom migration barriers, substrate temperature, and deposition rate is discussed. Modification of the system to improve adverse conditions by intermixing, alloying, and the use of surfactants is outlined. VW growth may also commence after completion of one or a few monolayers (MLs) in FM mode. This form of island growth, also known as Stranski-Krastanov (SK) growth, is mainly due to electronic effects, but may also be triggered by epitaxial strain relief. The tailoring of growth into FM-like growth, when VW or SK conditions exist-by an appropriate increase of supersaturation usually effected by controlling the substrate temperature and deposition rate, is briefly discussed.

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