Resonant Raman and FIIR spectra of carbon doped GaN

Intentionally carbon (C) doped (0 0 0 1)GaN was grown using C2H2 on a sapphire substrate by metalorganic vapor phase epitaxy. Optical spectra of the heavily doped samples were investigated at room temperature. In Raman spectra excited by the 325 nm line of a He-Cd laser, multiple LO phonon scattering signals up to 7th order were observed, and the A(1)(LO) phonon energy was determined to be 737.5 cm(-1) (91.45 meV). In infrared reflectance spectra, on the other hand, a local vibration mode was found at 777.5 cm(-1), which is attributed to a Ga-C bond in the GaN matrix suggesting that the C sits on an N site (C-N). In spite of the strong suggestion of C-N, the samples did not show p-type conduction. Possible origin of the carrier compensation is discussed in relation to the enhancement of defect related yellow luminescence in the photoluminescence spectra. (C) 2014 Elsevier B.V. All rights reserved.