Photoluminescence (PL) and optically detected magnetic resonance (ODMR) experiments have been performed on a set of GaN epitaxial layers grown by organometallic chemical-vapor deposition. Both undoped and Mg-doped GaN films were investigated. Samples were studied from three laboratories to obtain general trends and behavior. The ODMR experiments on the undoped films reveal resonances from both effective-mass and deep-donor states. These two features appear in all of the undoped GaN films and are most likely associated with an intrinsic point defect or defects. The same two donor resonances and a Mg-related quasideep acceptor resonance are found from the ODMR experiments on the Mg-doped samples. The energy level of the deep-donor state is found from ODMR spectral studies to be ∼1 eV below the conduction-band minimum. The PL experiments provide evidence for shallow acceptors in the undoped films and in a GaN sample lightly doped by residual Mg in the growth reactor. Models are proposed that describe the capture and recombination among these shallow- and deep-donor and acceptor states. The assignments of the magnetic resonance features are compared with the latest theoretical calculations of defect states in GaN.

• Received 26 January 1995

DOI:https://doi.org/10.1103/PhysRevB.51.13326