First-principles prediction on the stability, structural and electronic properties of AlGaN nanowires with point defects

Abstract AlGaN nanowires are promising for deep ultraviolet optoelectronic applications, but their performance is significantly affected by defects, and the mechanism of defect regulation remains unclear. In this work, the effect of vacancy and interstitial defects on the stability, structural and electronic properties of AlGaN nanowires are systematically investigated via first-principles. Our results demonstrate that the N vacancy exhibits the lowest formation energy of 3.68 eV, indicating that it is the most thermodynamically favorable defect type in AlGaN nanowires. Besides, as the defect position migrates from the center to the surface layer of nanowires, the stability of N vacancy gradually decreases (formation energy increases from 3.68 eV to 4.56 eV), while that of Ga vacancy progressively enhances (formation energy decreases from 8.06 eV to 7.88 eV). In addition, the introduction of defects induces significant relaxation in the atomic structure, with bond length variations up to 4.35% ∼ 7.50% for Ga-Ga around N vacancy and 9.92% ∼ 13.95% for N-N around Ga vacancy. Despite the incorporation of point defects, AlGaN nanowires preserve the direct bandgap characteristic. Moreover, Al vacancy, Ga vacancy and N interstitial introduce shallow acceptor levels at 0.12 ∼ 0.37 eV above the valence band maximum, while N vacancy, Ga interstitial and Al interstitial induce deep donor levels at 0.42 ∼ 1.58 eV below the conduction band minimum. Furthermore, Mulliken charge calculations reveal that atomic charge alterations induced by defects mainly occur within the neighboring coordination shell, verifying the localized nature of defect effects.