INVESTIGATION OF THE ANNHILATION OF POSITRONS IN DISTURBED SURFACE LAYERS OF GaAs.

Separation of the narrow component I//N from correlation curves obtained in the presence of a 14. 5 kG static magnetic field and measurements of the relative yield of the three-photon annihilation P//3// gamma were used in a study of the annhilation of positrons in disturbed surface layers of GaAs. These layers were subjected to the following treatments: a) grinding with an aqueous suspension of the M-5 Al//2O//3 abrasive powder; b) mechanical polishing with the ASM-1 diamond paste; c) chemomechanical polishing in an Al//2O//3 suspension; d) chemical polishing in a 1HF:3HNO//3:2H//2O mixture. The maximum values of I//N and P//3// gamma were obtained for samples which were chemically polished. These experimental observations, together with the proposed mechanism of positron annihilation in GaAs, led to the conclusion that an oxide film of complex composition was thicker on the chemically polished samples than on the samples subjected to the other three treatments.