Surface reconstructions of GaAs(100) observed by scanning tunneling microscopy.

Abstract

We present atomic-resolution images, obtained with scanning tunneling microscopy (STM), of the various reconstructions of smooth, in situ grown GaAs(100) surfaces. The outermost layer of the c(4\ifmmode\times\else\texttimes\fi{}4) reconstruction consists of three As-As adatom dimers parallel to [011]. Cells containing two or three As-As dimers have been observed on the 2\ifmmode\times\else\texttimes\fi{}4 surface. The ``1\ifmmode\times\else\texttimes\fi{}6'' surface seen in low-energy electron diffraction has a 2\ifmmode\times\else\texttimes\fi{}6 unit cell containing two As-As dimers. Diffraction patterns implying 4\ifmmode\times\else\texttimes\fi{}6 symmetry are seen to arise from the coexistence of 2\ifmmode\times\else\texttimes\fi{}6 and 4\ifmmode\times\else\texttimes\fi{}2 units. The c(8\ifmmode\times\else\texttimes\fi{}2) surface is made up of two Ga-Ga dimers and two missing dimers per 4\ifmmode\times\else\texttimes\fi{}2 cell. Atomic models, which are consistent with both the STM images and electron-counting heuristics, are also shown.