Magnetic resonance experiments, including optically detected magnetic resonance and electron paramagnetic resonance, were performed on Si-doped homoepitaxial GaN layers grown by MOCVD and on high quality, free-standing (~200μm-thick) GaN grown by HVPE. This made it possible to obtain information on the properties of native defects and dopants in GaN with a significantly reduced density of dislocations (<107/cm2) compared to that typically observed (about 5 x 108 to 1010/cm2) in conventional heteroepitaxial GaN layers. The high structural and optical quality of the layers was revealed by cross-sectional transmission electron microscopy and detailed low-temperature photoluminescence studies, respectively. Optically detected magnetic resonance at 24GHz on strong shallow donor–shallow acceptor recombination from the Si-doped homoepitaxial layer reveals evidence for Si or C shallow acceptors on the N sites. Electron paramagnetic resonance of the new free-standing HVPE GaN confirmed the low concentration of residual donors (~1016/cm3) as determined by Hall effect measurements. In addition, new deep centers were found from optically detected magnetic resonance on the 2.4eV, so-called green, photoluminescence band and on the broad emission less than 1.8eV from the HVPE GaN template. However, contrary to expectations, the reduction of random strain fields (associated with dislocations) had not led to significant changes in the character of the magnetic resonance (such as resolved electron-nuclear hyperfine structure) compared to that typically found for heteroepitaxial GaN layers.

Magnetic Resonance Studies of Defects in GaN with Reduced Dislocation Densities. E.R.Glaser, J.A.Freitas, G.C.Braga, W.E.Carlos, M.E.Twigg, A.E.Wickenden, D.D.Koleske, R.L.Henry, M.Leszczynski, I.Grzegory, T.Suski, S.Porowski, S.S.Park, K.Y.Lee, R.J.Molnar: Physica B, 2001, 308-310, 51-7