Local Vibration Modes for Determining the Ge Ga + Fingerprint Peak in Gallium Nitride (GaN) via First-Principles Calculations

Abstract Highly conductive silicon-doped gallium nitride (GaN) is commonly used in high-power optoelectronics and electronics. Alternatively, germanium (Ge) can achieve a higher doping concentration than silicon, as its atomic size is similar to that of Ga. Precisely understanding and controlling the atomic structure of Ge-doped GaN is necessary to enhance the electrical performance of GaN materials. While Raman spectroscopy can present localized vibration mode (LVM) fingerprint peaks that exhibit Raman activity caused by doping, determining the atomic structure of point defects through fingerprint peaks remains challenging. In this study, we estimated the phonon spectrum and LVMs of Ge-doped GaN using density functional theory. Additionally, we calculated the Raman spectra through bond polarization to obtain the atomic structure and vibration modes corresponding to fingerprint peaks. According to the formation energy, GeGa+ was the most likely defect to form. A comparison between the phonon density of states of bulk and defective structures located the fingerprint peak at 547.0 cm–1. Additionally, the LVMs exhibited a phenomenon similar to rotational displacement patterns, which may be related to the symmetry breaking at the Ge site. This study improves the understanding of how the structure of Ge-doped GaN affects variations in its material properties.