SURFACE RECONSTRUCTIONS OF GAAS(100) OBSERVED BY SCANNING TUNNELING MICROSCOPY

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(4×4) reconstruction consists of three As-As adatom dimers parallel to [011]. Cells containing two or three As-As dimers have been observed on the 2×4 surface. The 1×6 surface seen in low-energy electron diffraction has a 2×6 unit cell containing two As-As dimers. Diffraction patterns implying 4×6 symmetry are seen to arise from the coexistence of 2×6 and 4×2 units. The c(8×2) surface is made up of two Ga-Ga dimers and two missing dimers per 4×2 cell. Atomic models, which are consistent with both the STM images and electron-counting heuristics, are also shown. © 1990 The American Physical Society.