Optical Centers in Cr-, Mn-, and O-Doped AlN and Their Thermodynamic Stability Designed by a Multiscale Computational Approach.

Abstract

The optical centers in AlN can frequently exist in various charge states and can be accompanied by many coexisting defect species, creating a complex environment where mutual interactions are inevitable. Therefore, it is an immediate quest to design AlN crystal growth protocols that can target a specific optical center of interest and tune its concentration while preventing the formation of other unwanted point defects. Here, we provide a powerful workflow for point defect engineering in wide band gap, binary semiconductors that can be readily used to design optimal crystal growth protocols through combining CALPHAD-based phase analysis, and ab initio defect calculations. We investigate technologically relevant chromium- and manganese-induced optical centers in AlN, followed by studying the impact of oxygen that can be unintentionally incorporated during crystal growth. We present the dominant defects in all three cases as a function of process parameters along with the optical signatures. In the case of both Cr and Mn doping, the Cr_Al and Mn_Al defects are most likely, and increasing nitrogen partial pressure tends to enhance their concentration. We show that it is possible to use nitrogen fugacity as a tool for tuning the intensity of optical signatures. We calculate the Cr_Al charge transition levels with respect to the valence-band maximum at 2.60 eV (E^+/-), 3.83 eV (E^0/-), and 5.41 eV (E^-/2-) and electron and hole capture transitions with luminescence bands centered at 2.82, 1.91, and 3.15 eV. Unlike the Cr doping, Mn aggregation is unlikely, and the Mn_Al-V_N is the most abundant defect after Mn_Al under most synthesis conditions. Oxygen tends to form complexes with V_Al, and O_N-V_Al is a prominent defect following O_N, with near-UV emission bands at 3.17, 3.26, and 3.81 eV. Our results agree with the available experimental optical signatures of Cr-, Mn-, and O-related centers and provide pathways on how to tune the luminous intensity of these centers through changes in growth conditions.