Study of defects in GaN grown by the two-flow metalorganic chemical vapor deposition technique using monoenergetic positron beams

Defects in GaN grown using metalorganic chemical vapor deposition were stud ied through the use of monoenergetic positron beams. For Mg-doped GaN, no l arge change in the diffusion length of positrons was observed before and af ter activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg-hydrogen pairs. For Si-doped G aN, the line-shape parameter S increased as carrier density increased, sugg esting an introduction of Ga vacancy due to the Fermi level effect. Based o n these results, we discuss the effects of the growth polar direction of Ga N 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 photolu minescence and transmittance spectra, and a Stokes shift of about 20 meV wa s observed. This difference was attributed to extended band-tail states int roduced by high concentrations of donors and acceptor-type defects in -c Ga N. (C) 2001 American Institute of Physics.