Positron annihilation lifetime spectra were obtained from a series of crystals with various carrier concentrations, and were analyzed by using numerical Laplace inversion techniques. Three notable features were observed, in that the average positron annihilation rate in n-type and semi-insulating material was almost the same, but was smaller than that in p-type material. Also, the width of the positron annihilation rate distribution in n-type and semi-insulating material was much broader than that in p-type material. Finally, the upper limit of the annihilation rate distribution shifted from 3.96/ns for p-type material to about 3.77/ns for n-type and semi-insulating material. These results indicated that, in n-type and semi-insulating material, both In and P vacancies (VIn, VP) could trap positrons while, in p-type material, only the In vacancy was a trapping site. The charge state of VIn and VP was deduced to be neutral.

Z.Q.Chen, X.W.Hu, S.J.Wang, S.Q.Li: Solid State Communications, 1996, 97[11], 951-6