STM analysis of defects at the GaAs(001)-c(4 × 4) surface

Atomic structure models of semiconductor surfaces consider usually ideal models based on density functional theory calculations. In reality, however, semiconductor surfaces exhibit a variety of defects which deviate from this ideal surface structure. Depending on their specific nature and amount, these defects can contribute significantly to the total energy of the surface. Furthermore, the electronic properties and consequently their specific reactivity towards adsorption processes can be modified significantly due to the existence of surface defects. Here, we present an analysis of different kinds of defects at the GaAs(001)-c(4 × 4) surface reconstruction. The surfaces were prepared by thermal decapping of GaAs(001) epilayers grown by molecular beam epitaxy and capped by an amorphous As cap. High resolution measurements with scanning tunneling microscopy were performed at room temperature and allowed the identification and atomic analysis of several different kinds of surface defects. Apart from other defects we found indications that approximately 3% of the surface dimers are incomplete, consisting only of one As atom instead of two.