Defects in samples which had been grown by means of metalorganic chemical vapour deposition were studied by using mono-energetic positron beams. In the case of Mg-doped material, no large change in the positron diffusion length was observed before and after Mg activation. This was attributed to the scattering of positrons by potentials which were associated with the electric dipoles of Mg-H pairs. In the case of Si-doped material, the line-shape parameter increased as the carrier density increased; thus suggesting the introduction of Ga vacancies due to the Fermi level effect. Although the optical properties of films which were grown in the Ga-face direction exhibited excitonic features, films which were grown in the N-face direction exhibited broadened photoluminescence and transmittance spectra. A Stokes shift of about 0.02eV was observed. This difference was attributed to extended band-tail states that were introduced by high concentrations of donors and acceptor-type defects in the latter samples.

Study of Defects in GaN Grown by the Two-Flow Metalorganic Chemical Vapour Deposition Technique Using Monoenergetic Positron Beams. A.Uedono, S.F.Chichibu, Z.Q.Chen, M.Sumiya, R.Suzuki, T.Ohdaira, T.Mikado, T.Mukai, S.Nakamura: Journal of Applied Physics, 2001, 90[1], 181-6