Strain and electronic structure of Ge nanoislands on Si(111)-7×7surface

Abstract

To study the relation between the strain and the electronic structure in two-dimensional (2D) Ge nanoislands on the Si(111)-$7\ifmmode\times\else\texttimes\fi{}7$ surface, we calculated the relation based on the density functional theory and measured with the angle resolved ultraviolet photoelectron spectroscopy (ARUPS) and the scanning tunneling microscopy (STM). In the calculation, the dangling-bond state at the strained adatom on the 2D Ge island (${S}_{Ge}^{R}$ state) shifts to lower energy at the rate of $\ensuremath{-}8.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{nm}$ with the height of the adatoms. The ARUPS spectrum shows a characteristic peak corresponding to the ${S}_{Ge}^{R}$ state, whose energy depends on the size of the Ge nanoisland. The state appears at $\ensuremath{-}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below the Fermi level for the small Ge islands (3.8--5 nm) and at $\ensuremath{-}0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for the large Ge islands. The height of the Ge islands estimated from the energy difference is consistent with a result of the STM measurement. The strain of Ge islands can be estimated from the electronic structure.