A scanning tunneling microscopy study of the GaAs(112) surfaces

The GaAs(112)A and B surfaces were prepared by molecular beam epitaxy (MBE) and characterized in situ by scanning tunneling microscopy (STM). Both sur faces an unstable. On the (112)A surface Eve facets with the orientations ( 111), {110} and {124} appear, while on the ((112) over bar)B surface four f acets with the orientations ((111) over bar)B, ((110) over bar) and ((113) over bar)B were observed. In both cases, the facets form depressions coveri ng the entire surface. In addition, total-energy calculations employing den sity-functional theory were carried out for these surfaces. For the (112)A surface a roof-like structure of {111} and {113} planes has the lowest calc ulated energy. According to the calculations, the ((112) over bar)B surface forms under As-rich conditions a roof-like structure of {(111) over bar} a nd {(113) over bar}B planes, and it decomposes under Ga-rich conditions int o {<(11)over bar>0} planes. The experimental and theoretical findings for t he {(112) over bar}B surface are in good agreement. The occurrence of {124} -facets on the (112)A surface was not taken into consideration in the calcu lations and needs to be investigated further. (C) 1999 Elsevier Science Ltd . All rights reserved.