Tunneling spectroscopy on compensating surface defects induced by Si doping of molecular-beam epitaxially grown GaAs(001)

Abstract

The compensating defects on the GaAs(001)-(2×4)/c(2×8) surface that are induced by Si doping have been studied by spatially resolved tunneling spectroscopy. Previous scanning tunneling microscopy studies have shown that as the Si doping level of molecular-beam epitaxially grown GaAs is increased, an increasing number of kinks form in the dimer-vacancy rows of the (2×4)/c(2×8) surface reconstruction. These kinks are believed to act as surface acceptors and result in pinning of the surface Fermi level. In this work, both voltage dependent imaging and spectroscopy show that negative charge is located at the kink sites. This confirms that they are surface acceptors. The spectroscopy is consistent with each acceptor being occupied by one electron. The surface Fermi level is found to be pinned near midgap. While no peak in the state density centered on the Fermi level is observed, gap states in the form of tails extending in from the band edges are observed near some kinks.