Surface mass transport and island nucleation during growth of Ge on laser textured Si(001)

Abstract

Substrates with controlled surface morphologies are used to quantify the kinetics of surface mass transport during Stranski-Krastanov growth of epitaxial nanostructures. Morphologies are modified by laser texturing; tightly focused nanosecond laser pulses are used to produce micron-scale dimples on the surface of Si(001) substrates. The areal densities of three-dimensional Ge islands formed by chemical vapor deposition on these modified substrates is measured by atomic force microscopy for a wide range of Ge coverages (3--10 ML), temperatures $(500<T<700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ and deposition rates $(0.003<F<0.3 {\mathrm{ML}\mathrm{}\mathrm{}\mathrm{s}}^{\ensuremath{-}1}).$ Island nucleation is enhanced at the vicinal surfaces surrounding the rim of the laser dimples, and, as a consequence, a denuded zone with a reduced island density surrounds each dimple. The width of the denuded zone can be as large as 50 times the island spacing and is created by extensive mass transport during the formation of the wetting layer. Mass transport is driven by chemical-potential gradients associated with the wetting-layer thickness, substrate vicinality, and the elastic relaxation of three-dimensional islands. We find excellent agreement between the data and a one-dimensional model calculation of diffusion and nucleation; the fit to the model gives a transport rate of ${\mathrm{Dn}}_{0}\ensuremath{\approx}1.5\ifmmode\times\else\texttimes\fi{}{10}^{5}{\mathrm{s}}^{\ensuremath{-}1}$ at $600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and an activation energy ${E}_{f}{+E}_{m}\ensuremath{\approx}1.3 \mathrm{eV}.$