ODMR studies of MOVPE-grown GaN epitaxial layers.

GaN epitaxial layers grown by MOVPE on Al2O3 substrates have been studied by optically detected magnetic resonance (ODMR) at 21 GHz. Undoped n-conducting, Mg doped high resistivity and Mg doped p-conducting layers have been investigated. The undoped sample reveals an excitonic near band-gap (3.47 eV) luminescence and a sharply structured infrared luminescence near 1.30 eV. The dominant ODMR signal observed in this sample is an orthorhombic spin S=5/2 center, due to isolated Fe(3+) on the gallium site. The GaN:Mg layers show a strong blue/near UV D-A emission band peaked at 3.2 eV and the 1.3 eV band. Four additional ODMR lines are observed on these bands. First the shallow donor resonance, second an anisotropic signal possibly related to the Mg-acceptor and finally two signals of unknown origin