C. Leberre et al., EVIDENCE OF 2 KINDS OF ACCEPTORS IN UNDOPED SEMIINSULATING GAAS - POSITRON TRAPPING AT GALLIUM VACANCIES AND NEGATIVE-IONS, Physical review. B, Condensed matter, 52(11), 1995, pp. 8112-8120
Positron-lifetime experiments have been performed in Zn-doped p-type a
nd undoped semi-insulating GaAs in the temperature range 20-300 K to i
nvestigate native point defects. In p-type materials with hole concent
rations of 10(15)-10(19) cm(-3), no evidence of positron trapping is o
bserved. The temperature dependence of the positron lifetime can be ex
plained in terms of lattice expansion associated with positron-phonon
coupling. Therefore, we ascribe it to delocalized positrons. In semi-i
nsulating GaAs, two kinds of accepters are detected with concentration
s in the range 10(15)-10(17) cm(-3): gallium vacancies and negative io
ns. The temperature dependence of the positron trapping at the Ga vaca
ncy exhibits a slope break at about 130 K. A weakly bound Rydberg-like
precursor state is invoked to explain this temperature dependence.