Unreconstructed As atoms mixed with (3 x 2) cells and (6 x 6) supercells in low As pressure epitaxy on GaAs(001)

摘要

Since the early days of GaAs molecular beam epitaxy, it has been understood that on the As-stabilized growth surface, As lies in the form of As_2 building blocks. At lower As pressure however, there is a transition to a (3 x 1) growth surface observable by reflection high-energy electron diffraction. Using in situ scanning tunneling microscopy, we provide an atomically resolved observation of this still As rich surface that displays unreconstructed As atoms in (1 x 1) cells as well as (3 x 2) and (6 x 6) reconstructed areas. Most surface As atoms do not display any dimer bonds. From the statistics of surface Ga atoms in sp~2 hybridization we propose that the background carbon acceptor impurities content is significantly reduced in the (3 x 1) growth.