Studies of positron-surface interactions in semiconductors using positron annihilation induced auger electron spectroscopy

A surface sensitive technique, Positron-Annihilation-Induced Auger-Electron Spectroscopy (PAES), is becoming a powerful tool available for studies of positron surface phenomena and characterization of semiconductor surfaces. In this paper the results of studies of Si(111) and GaAs(100) surfaces using PAES are analyzed by performing quantum mechanical calculations of positron surface states and annihilation characteristics for the reconstructed Si(111)-(7x7) surface and for both As- and Ga-rich (100) surfaces of GaAs with c(2x8), (2x4), and c(4x4) reconstructions. Estimates of the positron binding energy, work function, and annihilation characteristics reveal their sensitivity to surface reconstruction and chemical composition of the topmost layers of semiconductors. Calculations show that the positron is getting trapped at the corner hole sites of the reconstructed Si(111)-(7x7) surface. It is shown that comparison of theoretical positron annihilation probabilities computed for different reconstructed GaAs(100) surfaces with experimental ones estimated from the measured Auger peak intensities permits identification of the chemical composition of the topmost layers of the GaAs(100) surface.