Tilting in the arsenic-induced c(4×4) reconstruction of the GaAs{001} surface

The atomic geometry of the As-rich GaAs{001}-c(4×4) surface prepared by molecular-beam epitaxy has been characterized in situ. The focus of the study is to determine how excess As affects the structure of the GaAs{001} surface. We report that the second- and third-interlayer spacings are (1.48±0.10) and (1.47±0.10), respectively, in comparison to the bulk spacing of 1.41. Arsenic atoms in the first layer are observed to be dimerized along the 110 azimuth with a bond length of (2.69±0.10). Furthermore, evidence is presented that is consistent with a structure which contains both untilted and tilted dimers. The tilting is defined by a rotation about the center of the dimer bond by ±(4.3°±0.5°). These results are based on desorbed Ga+ ion distributions obtained by shadow-cone-enhanced secondary-ion mass spectrometry.