The structure of vicinal (111) surfaces of perfect and dislocation-rich Ge crystals doped with Ga

Abstract

The authors have investigated by means of both scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED) Ge(111) vicinal surfaces misoriented by 1 degrees and 2 degrees toward the (112) and (112) high-symmetry directions. Surfaces of moderately Ga-doped (dopant concentration (DC) approximately=1*1019 cm-3) Ge reconstruct c(2*8). No straight step edges but meandering kinks between terraces are observed with the STM. For highly Ga-doped (DC approximately=2*1020 cm-3) Ge crystals rich in dislocations and Ga inclusions, the vicinal surfaces mentioned exhibit at room temperature the previously reported LEED pattern for a phase of the well oriented clean Ge(111) surface appearing at approximately 300 degrees C. STM images at room temperature clearly display the incommensurate honeycomb-domain reconstruction, I(2*2), proposed by Phaneuf et al. (1985) in order to explain the LEED pattern. High dislocation density and misorientation appear to be essential in order to observe this reconstruction. This is, to the best of their knowledge the first real-space observation of such a structure.