Study Of Heavy Ion Radiation Effects Of GaN HEMT Devices

Gallium nitride（GaN）has been widely used in satellite communication,radar and nuclear reactor due to its excellent physical and chemical properties.Although AlGaN/GaN high electron mobility transistor（HEMT）has shown great advantages in high frequency and high power applications,there is a lack of authoritative and unified understanding of its radiation effect mechanism at home and abroad.Therefore,based on AlGaN/GaN HEMT devices,the single event effect and displacement damage effect caused by heavy ion radiation are systematically studied in this thesis.The single event effect of AlGaN/GaN HEMT device has been studied.In the off-state,when the drain voltage reaches 40 V,the gate and drain current increase significantly,when the drain voltage reaches 100 V,the source current increases significantly,when the drain voltage reaches 150 V,the single event burnout occurs.In the semi-on state,when the drain voltage reaches 30 V,the gate current increases by two orders of magnitude,and the gate Schottky degradation is serious.In the on-state,there is no obvious single event effect.It is considered that the damage caused by heavy ion radiation is the most serious under off-state stress.Heavy ion radiation induces defects in AlGaN layer and GaN buffer layer,resulting in leakage path between gate drain and source drain.The simulation of single event effect of AlGaN/GaN HEMT device has been carried out.By changing different bias conditions,it is found that the single event effect is most obvious in the off-state;by changing different incident positions,it is found that the peak value of transient current is the highest when the drain is incident,and the pulse width of transient current is the widest when the gate is incident;by changing different LET,it is found that the higher the LET,the higher the transient current peak,the wider the pulse width,and the greater damage to the device;by changing different incident angles,it is found that the greater the incident angle,the more serious the damage.The displacement damage effect of AlGaN/GaN HEMT devices induced by heavy ion radiation is studied.When the heavy ion radiation fluence is 1×10⁸ ions/cm² and 1×10⁹ions/cm²,the gate reverse leakage current decreases slightly,and the heavy ion radiation induces a potential oxide barrier at the interface,which reduces the gate leakage current.After 1×10¹⁰ ions/cm² heavy ion irradiation,the electrical characteristics of the device are seriously degraded,the threshold voltage is shifted by 25%,and the drain saturation current is obviously degraded.Through EMMI,it is found that the number of"hot spots"increases and radiation defects are introduced at high radiation fluence.By analyzing the C-V characteristics of the heterojunction,it is found that the heavy ion radiation leads to the formation of defect trapped electrons at the AlGaN/GaN interface,resulting in the decrease of carrier concentration.The heavy ion radiation defects of AlGaN/GaN HEMT devices were characterized by pulse test,low frequency noise and photoluminescence.Different quiescent bias and different pulse width were used to test the surface defects of the device after heavy ion radiation.By comparing the results of different pulse width before and after radiation,it is found that the time constant of surface state trap induced by heavy ion radiation is more concentrated in the range of 500 ns～10μs.Through the characterization of low-frequency noise,it is found that with the increase of heavy ion radiation fluence,the defect density of noise extraction increases gradually.The defects induced by heavy ion radiation will increase the parasitic series resistance of AlGaN/GaN HEMT devices.The results show that the BL increases obviously after the heavy ion irradiation.It is considered that more VGa is introduced by the heavy ion irradiation,resulting in the formation of NGa defects.