The charge states of surface As vacancies on the (110) surface of p-type material were determined directly by means of scanning tunnelling microscopy. This method exploited a compensation between local band bending that resulted from the As vacancy and a p-type dopant whose charge states were known  a priori. A detailed analysis revealed a one-to-one compensation between the dopant-related and As vacancy-related features. This indicated that the As vacancy had a charge of +1. The method could be extended so as to determine quantitatively the charge states of other positive or negative point defects.

K.J.Chao, A.R.Smith, C.K.Shih: Physical Review B, 1996, 53[11], 6935-8