Mixed Ge-Si Dimer Growth at the Ge/Si(001)-(2×1) Surface

The submonolayer growth of Ge on single domain Si(001)-( $2\times 1$) has been studied using high resolution photoemission by monitoring the Ge $3d$ and Si $2p$ core levels as functions of coverage, electron emission angle, and annealing temperature. It is shown that Ge initially grows as asymmetric mixed Ge-Si dimers with Ge occupying the up atom and Si occupying the down atom sites. Although this growth mode is predominant up to 0.8 monolayer coverage, pure Ge-Ge dimers do occur as well as Ge substitution of second and perhaps deeper layer Si. This interdiffusion is enhanced upon annealing to 600 °C.