Defects in GaN grown using metalorganic chemical vapor deposition were studied through the use of monoenergetic positron beams. For Mg-doped GaN, no large change in the diffusion length of positrons was observed before and after activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg–hydrogen pairs. For Si-doped GaN, the line-shape parameter S increased as carrier density increased, suggesting an introduction of Ga vacancy due to the Fermi level effect. Based on these results, we discuss the effects of the growth polar direction of GaN on optical properties in this article. Although the optical properties of a GaN film grown toward the Ga face direction exhibited excitonic features, a film grown toward the N face (−c) direction exhibited broadened photoluminescence and transmittance spectra, and a Stokes shift of about 20 meV was observed. This difference was attributed to extended band-tail states introduced by high concentrations of donors and acceptor-type defects in −c GaN.

A positron pulsing system has been constructed for variable energy positron lifetime spectroscopy. The system consists of a reflection type chopper, a sub-harmonic prebuncher, and a double harmonic buncher. By operating the system with an intense slow positron beam generated by an electron linac, positron lifetime spectra have been successfully measured in an extended time range of more than 45 ns with a good time resolution (250 ps). Furthermore, Doppler broadening profiles of annihilation radiations can be obtained simultaneously with the lifetime measurements.

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Annealing properties of defects in F+- and B+-implanted Si were studied using monoenergetic positron beams. For F+-implanted specimen with a dose of 2×1013 F/cm2, before annealing treatment, the mean size of the open volume of defects was estimated to be close to the size of divacancies. After rapid thermal annealing (RTA) at 700° C, vacancy-fluorine complexes and vacancy clusters were formed. The mean size of the open volume for the vacancy-fluorine complexes was estimated to be close to the size of monovacancies, and their annealing temperature was determined to be 800° C. For F+-implanted specimen with a dose of 4×1015 F/cm2, complexes between vacancy clusters and fluorine atoms were introduced during solid-phase epitaxial growth of the amorphous region, and they were observed even after RTA at 1100° C. Effects of additional B+ implantation on annealing properties of defects are also discussed.