Thermal conductivity of GaN with a vacancy and an oxygen point defect

GaN has high thermal conductivity, therefore it is expected to be used in high-power, high-frequency, and compact electronic devices. However, GaN includes many defects and impurities, which reduce its thermal conductivity. Therefore, the effect of defects and impurities on the thermal conductivity of GaN needs to be understood for optimal thermal management. In this study, the thermal conductivity of GaN in three cases – with a Ga vacancy, an N vacancy, and an O impurity substituted at an N site – was investigated using first-principles calculations. Thermal conductivity was calculated based on the Boltzmann transportation equation under the relaxation time approximation. At 300 K, the thermal conductivity values of pure GaN and GaN with a Ga vacancy, an N vacancy, and an O substitutional impurity (defect concentrations$\sim 1.3\times 10$²¹ cm⁻³) were 325, 74, 70, and 138 W/(m K), respectively. It was found from the spectrum of thermal conductivity that acoustic phonons at frequencies lower than 10 THz were responsible for most of the thermal conductivity of GaN. We also examined the effect of sample size on thermal conductivity and found that the cumulative thermal conductivity value of pure GaN was less than 9% of the bulk value, when the sample size was smaller than 100 nm.