Temperature Dependence Cross-Sectional Study of Ammonothermal Gallium Nitride

Gallium nitride (GaN) is increasingly recognized as a popular material in the field of power electronics, optoelectronics, and high-frequency applications due to its advantageous properties, such as wide bandgap, high electron mobility, and good thermal conductivity. Hence, characterizing GaN is vital for optimizing its performance in various applications. In this study, we investigate the far-field infrared (IR) properties of Ammonothermal GaN wafers and their temperature-dependent behavior, utilizing a custom-built Fourier-transform infrared (FTIR) microscope setup. The setup has the ability to take measurements varying from 5 to 500 degrees of kelvin. The low defect density, scalability, and exceptional material properties of ammonothermal GaN make it highly advantageous for a range of applications. A set of Oxygen-doped (n-type), and Manganese-compensated (semi-insulating) Ammonothermal GaN samples were examined in this research. Our results reveal variations in the reststrahlen band as a function of temperature, which correlate with existing studies using different methods in the high temperature regime. Furthermore, we utilize the transverse optical (TO) and longitudinal optical (LO) phonon model to extract the model parameters of the material that leads to the observation of a red shift in the LO phonon mode. This shift suggests alterations in the lattice dynamics as temperature varies. Another distinctive feature of our investigation is the focus on the cross-section of the GaN material, which allows for the excitation of both in-plane and out-of-plane phonon components. This contrasts with traditional top-down measurement techniques that typically only engage in-plane phonon dynamics. By capturing both components as well as the effect of change in temperature, our study provides a more comprehensive understanding of GaN's dielectric properties and its phonon behavior. Overall, our findings contribute significantly to the characterization of GaN, enhancing the fundamental understanding of its thermal and dielectric responses. Such studies are crucial for the advancement of next-generation GaN-based devices, such as improving device efficiency, performance, and reliability.