First-principles study of charge states effects of nitrogen vacancies on phonon properties in III-nitride semiconductors

Understanding the effects of defects on the phonon-related properties of III-nitride semiconductors is important for device applications. However, the effect of the charge-state difference on the phonon-related properties of defects has not been studied. This study calculated the phonon bands of AlN and GaN for pristine crystals and crystals with +1 or +3 nitrogen vacancies (VN1+ or VN3+). Our results revealed distinct differences in the phonon bands, density of states (DOS), and infrared (IR) spectra between pristine and defective crystals, particularly between VN1+ and VN3+. The VN3+ exhibited a larger disturbance in the phonon bands than VN1+. The VN3+ exhibited more peaks and larger peak intensities in the DOS than VN1+. The IR spectrum intensity of A1(TO) was larger than that of E1(TO) in the VN3+, which was different from the pristine and VN1+ cases. In the IR spectrum of VN3+ in GaN, a small peak appeared to represent a defect. These results imply that the effects of vacancies on the phonon-related properties depend not only on the concentration but also on the charge state. This study can serve as a guide for future in-depth research on the effect of defects on thermal properties.