Microscopic mechanism of the homoepitaxy onSi(111)7×7

Abstract

Very initial stages of the homoepitaxy on the $\mathrm{Si}(111)7\ifmmode\times\else\texttimes\fi{}7$ surface are studied at 310, 356, and $366{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ by in situ continuous observation using high-temperature scanning tunneling microscopy (HTSTM) at the atomic scale during Si deposition under a slow rate of 0.02 bilayer $(\mathrm{BL})\phantom{\rule{0.16em}{0ex}}{min}^{\ensuremath{-}1}$. The substrate surface is reconstructed to the well-established dimer-adatom-stacking fault (DAS) structure with the $7\ifmmode\times\else\texttimes\fi{}7$ unit cell consisting of two triangular half unit cells (HUCs): a stacking faulted (F)-HUC and a normally stacked one. It is expected that the complex, large unit cell compels the initial homoepitaxy to proceed in a quite different manner from that on unreconstructed surfaces. Formation and growth of various adsorbed clusters are pursued by the continuous observation of the same narrow areas during the deposition, avoiding the tip-shadow effect. The most anomalous finding is a quasiliquid cluster (QLC) spreading to plural HUCs (spread QLC) on the $7\ifmmode\times\else\texttimes\fi{}7$ DAS substrate. This appears as a result of the difficulty of the F-HUC to be transformed into the normally stacked BL, being essential for the homoepitaxy. After the transformation, the spread QLC undergoes the following structural changes with an increase of the Si deposition: crystallization to a small epitaxial BL \ensuremath{\rightarrow} surface reconstruction to the DAS structure. Validity and reasons of the transitional formation of the spread QLC are discussed. The spread QLC mediated homoepitaxy mechanism is concluded and is a new mode in the crystal growth. Real in situ HTSTM observations of the same areas on the nanoscale during Si deposition are indispensable to explore for the dynamic atomistic mechanism of the homoepitaxial growth on the $\mathrm{Si}(111)7\ifmmode\times\else\texttimes\fi{}7$.