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

TLDR

The study presents atomic‑resolution STM images of various reconstructions of smooth, in‑situ grown GaAs(100) surfaces. The STM analysis reveals that the c(4×4) surface has three As‑As adatom dimers parallel to [011], while the c(8×2) surface contains two Ga‑Ga dimers and two missing dimers per 4×2 cell. The study identifies 2×4 cells with two or three As‑As dimers, a 1×6 surface comprising a 2×6 unit cell with two dimers, and diffraction patterns indicating 4×6 symmetry from coexisting 2×6 and 4×2 units, and presents atomic models that agree with STM data and electron‑counting rules.

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.