Electrical, optical, and defect properties of carbon-doped gallium nitride grown by molecular-beam epitaxy

The electrical and optical properties of carbon-related defects in GaN:C, both semi-insulating and n-type conducting material, have been evaluated by a variety of characterization techniques including photoluminescence, electrical resistivity, photoconductivity, thermally stimulated current, deep-level transient spectroscopy, Raman scattering, positron annihilation spectroscopy, and low-frequency noise spectroscopy.; Carbon has been found to introduce at least two, and probably three, different types of point defects. These are identified as the C_N acceptor, tentatively the CGa DX-donor for the second defect, and most probably a third deep-acceptor defect related to interstitial carbon. The C_N acceptor shows an optical ionization energy of 220 meV, and an thermal ionization energy of 150 meV estimated indirectly from thermal quenching of a luminescence process believed to be related to this defect.; It was found from a comparison of the gallium vacancy concentration, carbon concentration, and the absolute intensity of the ∼2.2 eV luminescence in a series of specially prepared samples that there are almost certainly two mechanisms contributing to the ∼2.2 eV luminescence usually observed in GaN.; The types of defects introduced by carbon in wurtzite GaN grown by MBE showed an anomalous dependence on the carbon flux supplied to the growth surface. The fraction of the total carbon incorporated in the form of C_Ga defects (rather than C_N) steadily increased as a function of doping level.; Carbon-doped GaN samples did not show acceptor-bound exciton luminescence transitions despite their high acceptor concentrations, and showed a strong blue (∼2.9 eV) luminescence band that dominated over shallow donor-acceptor pair transitions. These observations were understood based on the carbon pairing phenomenon.; As a consequence of the anomalous concentration dependent carbon defect formation behavior, the net acceptor concentration introduced by carbon decreased with increasing carbon concentration. This prevented p-type conductivity and caused the resistivity of semi-insulating GaN:C to decrease above a certain carbon concentration. Extremely heavily doped material was actually n-type conducting rather than semi-insulating. (Abstract shortened by UMI.)...