Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon

The impact of C incorporation on the deep level spectrum of n-type and semiinsulating GaN:C:Si films grown by rf plasmaassisted molecularbeam epitaxy ( MBE ) was investigated by the combination of deep level transient spectroscopy, steadystate photocapacitance, and transient deep level optical spectroscopy. The deep level spectra of the GaN:C:Si samples exhibited several bandgap states. A monotonic relation between systematic doping with C and quantitative trap concentration revealed C related deep levels. A deep acceptor at E-c-2.05 eV and a deep donor at E-c-0.11 eV are newly reported states, and the latter is the first directly observed deep level attributed to the C-Ga defect. A configurationcoordinate model involving localized lattice distortion revealed strong evidence that C- related deep levels at Ec-3.0 eV and E (v)+0.9 eV are likely identical and associated with the yellow luminescence in Cdoped GaN films. Of the deep levels whose trap concentration increase with C doping, the bandgap states at E-c-3.0 and 3.28 eV had the largest concentration, implying that freecarrier compensation by these deep levels is responsible for the semi- insulating behavior of GaN:C:Si films grown by MBE. The differing manner by which C incorporation in GaN may impact electrical conductivity in films grown by MBE and metalorganic chemicalvapor deposition is discussed. (c) 2005 American Institute of Physics.