POSITRON-ANNIHILATION STUDIES OF DEFECT PROPERTIES IN SEMIINSULATING GAAS

The positron lifetime spectra have been measured in three semi-insulat ing (SI) GaAs samples, one n-type GaAs doped with Te, and one p-GaAs d oped with Zn. The average lifetimes in all SI-GaAs samples were approx imate to 229 ps, and were larger than the bulk lifetime found in p-GaA s. Moreover, the annihilation rate distribution (ARD) in SI-GaAs was m uch wider than that in p-type GaAs. This showed that gallium vacancies existed in SI-GaAs. By measuring its Doppler broadening spectra as a function of temperature between 10 and 300 K, we observed that the S-p arameter decreased with temperature increasing from 10 to 120 K. Thus the charge state of V-Ga was determined to be negative. Another defect V-As in SI-GaAs has also been detected under photoexcitation at 77 K by the increase of the S-parameter with the driving current in GaAs LE D which was not observed in the dark.