Optical property in colorless AlN bulk crystals: investigation of native defect-induced UV absorption

Abstract The 4.7 eV absorption band of colorless AlN crystal with the carbon concentration level of 107 cm−3 is investigated. An analysis of the absorption characteristics of the annealed AlN crystal indicates that the native defect is the origin of 4.7 eV absorption band and gives rise to an infrared absorption band at 2850 cm−1. The theory calculations predict two absorption bands at 4.65 eV and 0.35 eV of nitrogen vacancy, and the defect explains the increased and decreased intensity of infrared absorption band at 2850 cm−1 as well as a similar increased-decreased ultraviolet absorption band at 4.7 eV.