Different Effects Of Mg And Si Doping On The Thermal Transport Of Gallium Nitride

Mg and Si as the typical dopants for p-and n-type gallium nitride(GaN),respectively,are widely used in GaN-based photoelectric devices.In the practical application of GaN-based optoelectronic devices,the performance and lifetime of the devices mainly lie with the heat dissipation efficiency in the active region.Experimentally,the thermal conductivity of GaN is significantly suppressed after doping with Mg and Si,but the physical mechanism is not clear.Insight into the thermal transport properties of Mg-and Si-doped GaN and the physical mechanism of thermal conductivity reduction after GaN doping,which have great scientific value and practical significance for improving the performance of devices and prolonging the lifetime of devices.In this study,based on the density function theory and phonon Boltzmann transport equation,the effects of Mg and Si doping on the thermal transport properties of GaN were investigated by using first-principles calculations.The innovation results can be summarized as follows:The thermal conductivities of Mg-doped GaN were calculated to be 5.11 and 4.77W/m K for in-plane and cross-plane directions,the thermal conductivities of GaN reach0.41 and 0.51 W/m K for in-plane and cross-plane directions after doping with Si,respectively.Compared with the 275 and 303 W/m K of pristine GaN in in-plane and cross-plane directions,respectively,the thermal conductivities of Mg-and Si-doped GaN are significantly reduced by two and three orders of magnitude,respectively.Meanwhile,the physical nature of the decrease of thermal conductivity caused by the doping of Mg and Si GaN was explored at the micro/nano scale,which can be summarized as three points: first,the decrease of in-plane and cross-plane thermal conductivities of Mg-doped GaN are both attributed to the combined effect of low group velocities of optical phonon branches and small phonon relaxation time.For Sidoped GaN,due to the different contributions of different phonon modes to the in-plane and cross-plane thermal conductivity,the decrease of in-plane thermal conductivity is mainly due to the extremely low phonon relaxation time,while the suppression of crossplane thermal conductivity is due to the joint action of low optical phonon group velocity and very low phonon relaxation time.Second,further analysis shows that the lattice anharmonicity enhancement promotes phonon-phonon scattering after GaN doping with Mg and Si,which greatly suppresses phonon relaxation time.Third,the analysis of electronic structure shows that the strong polarization of Mg-N and Si-N bonds and the distortion of the local structures together enhance the anharmonicity of lattice,which indirectly explains the sharp decrease of thermal conductivities of Mgand Si-doped GaN.In this study,the effects of Mg and Si doping on the thermal transport properties of GaN were clarified from the atomic and electronic scales,and the fundamental mechanism of the significant reduction of thermal conductivity was revealed,which would provide guidance for the thermal management of GaN-based photoelectric devices.