Resonant Raman and FTIR spectra of carbon doped GaN

Abstract

Intentionally carbon (C) doped (0001)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 325nm 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 737.5cm−1 (91.45meV). In infrared reflectance spectra, on the other hand, a local vibration mode was found at 777.5cm−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.