Resonant Raman and FTIR spectra of carbon doped GaN

• Carbon is intentionally doped into GaN using C2H2 in the MOVPE growth.
• A1(LO) phonon energy was determined to be 737.5 cm−1 by resonant Raman spectra, and local vibration mode related to carbon doping was found out at 777.5 cm−1 in the FTIR spectra.
• Possible origin of the carrier compensation suppressing p-type conduction was discussed in relation to the defect related yellow luminescence band.

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 A1(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 (CN). In spite of the strong suggestion of CN, 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.