Low-temperature growth of crystalline gallium nitride films using vibrational excitation of ammonia molecules in laser-assisted metalorganic chemical vapor deposition

Low-temperature growth of crystalline gallium nitride (GaN) films on c-plane sapphire (α-Al₂O₃) substrates was achieved by laser-assisted metalorganic chemical vapor deposition (LMOCVD) and coupling laser energy into the chemical reactions. Trimethylgallium (TMGa) and ammonia (NH₃) were used as precursors for the growth of GaN films. Through the resonant excitation of rotational-vibrational transition (1084.71 cm^-1) of the NH-wagging mode (v₂) in NH₃ molecules using a wavelength-tunable CO₂ laser tuned at 9.219 μm, highly c-axis oriented GaN films were deposited on sapphire at low substrate temperatures from 250 to 600 °C. GaN films with a large thickness of 12 μm were obtained within 1 h at a substrate temperature of 600 °C. The GaN films deposited by LMOCVD showed a higher degree of crystallinity, higher growth rate, and lower defect densities as compared to those synthesized by MOCVD without resonant excitation of NH₃ molecules. This low-temperature synthesis technique opens a promising approach to growing nitrides with low adverse effects.