Roughness and correlations in the transition from island to film growth: Simulations and application to CdTe deposition

Highlights: • Simulations of deposition during island growth, coalescence, and film formation. • Island density is controlled by diffusion on the substrate. • Morphology in island coalescence and film formation is controlled by ES barrier. • Maximal roughness of CdTe films as islands coalesce indicates negligible barriers. Using kinetic Monte Carlo simulations, we relate morphological properties and microscopic dynamics during island growth, coalescence, and initial formation of continuous heteroepitaxial films. The average island width is controlled by adatom mobility on substrate. Subsequent evolution strongly depends on the Ehrlich-Schwöebel energy barrier $E_{\mathrm{ES}}$ of the deposited material. As $E_{\mathrm{ES}}$ decreases, islands become taller and their coalescence is delayed. For small islands and large $E_{\mathrm{ES}}$, the global roughness increases as $W~{\mathrm{thickness}}^{1/2}$ and the local roughness increases at short scales (apparent anomalous scaling) before and after island coalescence. If the islands are wide, W may have a plateau for large $E_{\mathrm{ES}}$ and has a maximum for small $E_{\mathrm{ES}}$ when the islands coalesce. This framework is applied to atomic-force microscopy data of the initial stages of CdTe deposition on Kapton: a maximum of W during island coalescence indicates negligible ES barrier, consistently with scaling properties of much thicker films, and the diffusion coefficient ${10}^{-7}—{10}^{-5}{\mathrm{cm}}^2/s$ on the Kapton surface at $150°C$ is estimated. Applications of the framework to other materials are suggested, in which the expected roles of ES barriers are highlighted.