Cesium-induced surface conversion: From As-rich to Ga-rich GaAs(001) at reduced temperatures

Abstract

We proved experimentally that Cs adsorption on the clean arsenic-rich $\mathrm{Ga}\mathrm{As}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}4)∕c(2\ifmmode\times\else\texttimes\fi{}8)$ surface followed by annealing at $450\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}--470\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, induced conversion to the $(4\ifmmode\times\else\texttimes\fi{}2)∕c(8\ifmmode\times\else\texttimes\fi{}2)$ gallium-rich reconstruction. Thus, the conversion temperature is lower by $\ensuremath{\sim}100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ than that required to produce the Ga-rich surface by a conventional ultrahigh vacuum annealing without preliminary Cs adsorption. This effect is monitored using low-energy electron diffraction, reflectance anisotropy spectroscopy, and photoreflectance spectroscopy. We propose that the conversion is due to Cs-induced weakening of arsenic bonds on the surface, which, in its turn, is supposedly caused by electron charge redistribution between Cs adatoms and GaAs surface atoms. Along with the transformation of surface stoichiometry and structure, Cs passivates intrinsic electronic surface states and thus leads to unpinned behavior of the Fermi level at the surface. In combination with the iodine-induced conversion from the Ga-rich to As-rich reconstruction, which was observed earlier, the reverse (As-rich to Ga-rich) low-temperature Cs-induced conversion presented here is promising for the development of atomic-layer etching of GaAs(001).