In situ scanning tunneling microscopy of GaAs(001), (111)A, and (111)B surfaces in sulfuric acid solution

In situ electrochemical scanning tunneling microscopy (STM) was used to examine n-type GaAs(001), (111)A, and (111)B surfaces in 0.05 M sulfuric acid. Cathodic polarization of the GaAs electrodes effectively inhibited the oxidation of the surface, making it possible to acquire STM images with atomic resolution. Atomically-flat terrace-step structures were consistently observed on all surfaces prepared by the chemical etching method. Steps observed on these surfaces are composed of double layers with step heights of 0.28 and 0.33 nm for the (001) and (111) surfaces, respectively. In situ STM atomic images revealed that those surfaces have (1×1) structures with the square and hexagonal lattices, respectively.