Structure of an $\mathrm{InAs}\left(111\right)\mathrm{}A-(2\mathrm{}\times 2)S$ surface studied by scanning tunneling microscopy, photoelectron spectroscopy, and x-ray photoelectron diffraction

The structure of an $\mathrm{InAs}\left(111\right)\mathrm{}A-(2\mathrm{}\times 2)S$ surface has been studied by using scanning tunneling microscopy (STM), synchrotron radiation photoemission spectroscopy (SRPES), and x-ray photoelectron diffraction (XPD). Honeycomblike images are observed by STM measured at a bias voltage of -1.4 V. Similar images are also observed at +1.5 V, although the intensity of the alternative corner of a hexagon is depressed, resulting in a threefold symmetry. $\mathrm{S}2s$ and $\mathrm{As}3d$ XPD patterns show that sulfur atoms rarely exchange the fourfold arsenic sites. Three surface components are found in the $\mathrm{In}4d$ spectra. On the other hand, no surface components are found in the $\mathrm{As}3d$ spectra. Based on the STM, SRPES, and XPD results, a probable structure model for the $(2\mathrm{}\times 2)S$ surface is proposed. The experimental XPD patterns are in good agreement with the calculated ones.