Study On Radiation Effects And Damage Mechanisms Of AlGaN/GaN HEMTs

With the development of space technology,spacecraft exhibit higher requirements for the performance of electronic systems.The performance of traditional semiconductor devices can no longer meet the requirements of aerospace engineering.AlGaN/GaN HEMTs show excellent application in the space equipment due to high frequency,high power,high temperature and high voltage.However,the total ionizing dose and displacement damage mechanism of AlGaN/GaN HEMTs has not been fully understood,which limits its application in aerospace engineering.In this paper,the domestic AlGaN/GaN HEMTs are studied by different radiation sources.Through experimental characterization and simulation methods,the mechanism of irradiation damage and ionization/displacement synergistic effect of AlGaN/GaN HEMTs are reveale and the equivalence of NIEL method was clarified.In order to accurately characterize the defects induced by different types of particles in the AlGaN/GaN HEMTs,based on the characteristics of the AlGaN/GaN HEMTs,an electroactive defect characterization method by monitoring the transient current was invented,which improved the defect testing accuracy and reliability.Through this method,it is confirmed that there are many different types of defects in GaN layer of AlGaN/GaN HEMTs,which are closely related to displacement radiation damage.The energy level of These defects are all located near E_C-0.9 e V.These defects induced by displacement damage will greatly reduce the electrical performance of devices.Based on the experimental and density functional theory,it is found that the possible defect types of the energy level are nitrogen interstitial,nitrogen di-vacancy and gallium vacancy.Through the irradiation and simulation analysis before and after hydrogen pretreatment,it is revealed that the gallium vacancy is the main defect in these defects,and the existence of hydrogen will form a more stable complex defect structure with gallium vacancy.This shows that the formation and evolution of defects in AlGaN/GaN HEMTs is a complex dynamic process and the dynamic evolution behavior is revealed based on molecular dynamics simulation.Through comprehensive analysis of the electrical performance degradation and defects evolution of the devices,it is revealed that the acceptor defect in the GaN layer is the main reason for the degradation.The defect concentration and the shift of threshold voltage are in a sub-linear relationship,and the electrical performance degradation caused by the defect whose energy level is close to the valence band is more obvious.When multiple defects exist at the same time,defects with deeper level will reduce the influence of other defects on performance degradation.Based on the above relationship,a degradation simulation method for AlGaN/GaN HEMTs was established by combining the first principle,Monte Carlo,molecular dynamics and TCAD simulation technology and the key electrical parameters predicted were consistent with the test results.By studying the degradation of electrical performance of AlGaN/GaN HEMTs caused by different energies and kinds of heavy ion irradiation,it is found that the displacement damage equivalent method based on NIEL value is not applicable to AlGaN/GaN HEMTs and the displacement damage of AlGaN/GaN HEMTs is not completely determined by the NIEL value.By matching the order of comprehensive irradiation of different particle sources,it is found that when the NIEL value of the incident particles in the AlGaN/GaN HEMTs is the same,the greater the ionization energy loss(IEL),the more displacement defects caused by radiation,and the greater the of displacement damage,which indicates that the AlGaN/GaN HEMTs has obvious ionization/displacement synergistic effect.By density functional theory simulation,it is revealed that the excited state caused by ionization effect will reduce the lattice atomic dislocation threshold energy in GaN,and promote the generation of displacement defects in devices.