Observation of As-Grown Defects in Zn-Doped GaAs by Positron Lifetime Spectra

Abstract

Positron lifetime spectra were measured for the Zn-doped p-type GaAs. In comparing the horizontal-Bridgmanmethod-grown and the A oating-zone-method grown p-type GaAs with the liquid-encapsulation-Czochralski-grown p-type GaAs samples, positron trapping into vacancy type defects was observed in the former two grown p-type GaAs. Shallow positron traps were detected, and the dominant ones were attributed t o acceptor the in p-type GaAs.P A C 3 78. 70. Bj Positron lifetime spectroscopy, which is directly sensitive to vacancy-type defects, is an established method for studying the defect in semiconductor.' Up to now, many works have been reported on ntype GaAs by and semi-insulating (SI)-type GaAs by using this technique and it has been proved to be s u c ~e s s f u l . ~-~ However, much less studies concerned about the p-type materials has been done. There is a discrepancy on positron trapping into defects in ptype GaAs. Some studies claimed that no positron trapping O C C U ~S , ~-~ but some other investigation argued that defects can be observed by positron in ptype G a A ~. ~-l l Dannefaer et al. found clear evidence of positron trapping in the p-type G ~A S . ~ Le Berre et al. found stronger temperature dependence of positron lifetime other than the simple thermal expansion, which was attributed to lattice expansion associated with positron-phonon ~o u p l i n g . ~ Wang et al. have also observed that the positron trapped into vacancy clusters in the deformed p-type GaAs." Fujii et al. found that interstitial clusters were introduced by Zn-doping." Thus, whether exist some defects that can be detected by positron measurement in p-type GaAs is still an open question, and this will be the subject of present work.