Epitaxial growth and quantum well states study of Sn thin films on Sn induced Si(111)-(2√3x2√3) R30° surface

Surface morphologies and electronic structures of Sri thin films prepared on Si(111)-Sn(2 root 3x2 root 3) R30 degrees substrate are investigated by low temperature scanning tunneling microscopy/scanning tunneling spectroscopy (STS). A typical Stranski-Krastanov growth is observed at various growth temperatures (95-300 K), and the Sn islands above wetting layers exhibit the preferential thicknesses of odd-numbered atomic layers. STS measurement shows the formation of well-defined quantum well states with an oscillation period of 2 ML, which modulates the surface energy and accounts for the observed preferential thicknesses. Due to the interplay between large lattice mismatch and symmetry difference, a transition from alpha-Sn to beta-Sn occurs at 4 ML, which confirms the previous report. From 4 to 11 ML, the mismatch resulted strain manifests the growth via thickness-dependent striplike modulation structures on the surfaces of all Sri islands. Upon room temperature annealing, the as-deposited Sri islands undergo a metal-insulator transition, while the band gaps of wetting layers increase and oppositely shift with respect to the Fermi level for n- and p-type substrates. The change in electronic property is attributed to the electron transfer at the Sn-Si interface, which also affects the growth and morphologies of films.