Infrared absorption of hydrogen-related defects in ammonothermal GaN

Polarization controlled Fourier transform infrared (FTIR) absorption measurements were performed on a high quality m-plane ammonothermal GaN crystal grown using basic chemistry. The polarization dependence of characteristic absorption peaks of hydrogen-related defects at 3000–3500 cm⁻¹ was used to identify and determine the bond orientation of hydrogenated defect complexes in the GaN lattice. Majority of hydrogen was found to be bonded in gallium vacancy complexes decorated with one to three hydrogen atoms (V_Ga-H_1,2,3) but also hydrogenated oxygen defect complexes, hydrogen in bond-center sites, and lattice direction independent absorption were observed. Absorption peak intensity was used to determine a total hydrogenated V_Ga density of approximately 4 × 10¹⁸ cm⁻³, with main contribution from V_Ga-H_1,2. Also, a significant concentration of electrically passive V_Ga-H₃ was detected. The high density of hydrogenated defects is expected to have a strong effect on the structural, optical, and electrical properties of ammonothermal GaN crystals.