Below band-gap optical absorption and photoluminescence excitation spectroscopy at room temperature in low-defect-density bulk GaN:Fe

We present a detailed study of the below band-gap optical absorption at room temperature in bulk semi-insulating GaN:Fe versus the Fe-doping. It was established that the 1.24 eV photoluminescence band at 300K consists of only vibrational replicas of the Fe 3+ 4 T 1 (G)→ 6 A 1 (S) internal transition. We also studied the below band-gap photoluminescence excitation of the 1.24eV band. The identical exponential rise of the photoluminescence excitation and the optical absorption coefficient identify the Fe 3+/2+ charge-transfer as the main contributor to the 300K optical absorption in the range 400-500nm. Practical implications of these results for Fe-doping determination are discussed.