Microstructural Evolution During the Epitaxial Growth of Ag/InP (100)

Abstract

The initial stages of epitaxial growth of Ag on InP(100) has been studied using in-situ and ex-situ electron microscopy techniques. Vicinal InP substrates were cleaned by heating to about 450°C in ultra-high vacuum. Silver was subsequently deposited at substrate temperatures between 350–500°C. The microstructural evolution was monitored for coverages between 0.5–8ML using high spatial resolution secondary electron microscopy and transmission electron microscopy. At sub-monolayer coverages, square islands of Ag are formed with edges aligned along InP directions. Subsequent deposition leads to secondary nucleation or growth of pre-existing islands, depending on the substrate temperature. Surfaces with a uniform distribution of steps have a higher island density than those without steps but the steps are not preferred sites for island nucleation. Coalescence of islands begins at a smaller coverage for lower temperatures and for stepped surfaces. At the early stages of coalescence, island shapes with low symmetry are formed, with diminished island heights. These subsequently transform into shapes of higher symmetry. Except at the highest temperatures studied (500°C), island shape transformations (e.g. from square to elongated) are not very significant. Plan view transmission electron microscopy shows that the islands are epitaxially aligned and that even the smallest islands are generally incoherent. Island size distributions are used to analyze the growth mechanisms.