Direct determination of exact charge states of surface point defects using scanning tunneling microscopy: As vacancies on GaAs (110)

We show a direct determination of the charge state of surface As vacancies on p-type GaAs(110) using scanning tunneling microscopy. This method utilizes the compensation between the local band bending resulting from the As vacancy and the p-type dopant whose charge states are known a priori. Detailed analysis shows a one-to-one compensation between the dopant-related and As-vacancy-related features, indicating that the As vacancy has a charge of +1. This method can be extended to determine quantitative charge states of other point defects (positive or negative). {} 1996 The American Physical Society.