Structure of an InAs(111)A-(2X2)S surface studied by scanning tunneling microscopy, photoelectron spectroscopy, and X-ray photoelectron diffraction

The structure of an InAs(111)A-(2 X 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. S 2s and As 3d XPD patterns show that sulfur atoms rarely exchange the fourfold arsenic sites. Three surface components are found in the In 4d spectra. On the other hand, no surface components are found in the As 3d spectra. Based on the STM, SRPES, and XPD results, a probable structure model for the (2 X 2)S surface is proposed. The experimental XPD patterns are in good agreement with the calculated ones.