Study On Novel Structure Of 4H-SiC Light Triggered Thyristor

As third generation semiconductor material,silicon carbide(SiC),which has wide bandgap,high thermal conductivity,high critical avalanche breakdown electric field and large saturation carrier driftvelocity,is one of the ideal materials for high temperature,high power and radiation-hardened power devices’fabricatiorn.As a semiconductor power device,SiC light triggered thyristor(LTT)has great advantages in simplifying drive circuits and enhancing the ability to resist electromagnetic interference.Over several years’ development,the researches on SiC LTT have obtained gratifying achievements both domestic and overseas.However,different from silicon(Si),there is low acceptor impurity ionization characteristic in heavily doped p-type SiC at room temperature.The low acceptor impurity ionization leads to low hole-injection in SiC p+n junction.And there are few studies about affects and action mechanisms of low hole-injection issue on SiC LTT characteristics.Therefore,basing on the systematically analysis of basic structure,working mechanism and electric characteristics,the numerical simulation model are set up to in estigate the formation mechanism and adverse effects of low hole-injection issue in SiC LTT.Aiming to improve the device’s performances,the theoretically and experimental researches are carried out on novel structure of 4H-SiC LTT.The main research contents and results are as follows:1.The formation mechanism of low hole-injection issue in SiC LIT p+n emitter junction and the influences of low hole-injection issue in p+n emitter junction on device performances of SiC LTT are investigated.The simulation results indicate that for p-type blocking base SiC LTT,the influences are mainly on minimum triggering light intensity and turn-on delay time.For n-type blocking base SiC LTT,the influences are mainly on on-state voltage drop.2.The structure scheme for enhancing hole-injection of p+n emitter junction is proposed.According to the formation mechanism of low hole-injection issue in p+n emitter junction and structure characteristic of SiC LTT,double-layer thin n-base,double-layer n-buffer,and NiO/SiC heterojunction are used to enhance the hole-injection in p+n emitter junction,weaken the adverse effects of low acceptor impurity ionization,and improve the performances of SiC LTT.The simulation results indicate that,by using double-layer thin n-base structure,the minimum triggering light intensity and the minimum turn-on delay time of p-type SiC LTT can be reduced by 11.8%and 45%,respectively.By using double-layer n-buffer structure,the on-state voltage drop of n-type SiC LTT can be reduced by 43.5%.By using the NiO/SiC heterojunction,the hole-injection ratio of p+n emitter junction in SiC LTT can be improved by about 1.53 × 108 times.3.The structure scheme for enhancing hole-transmission of n-base is proposed.According to the influence mechanism of low hole-injection in p+n emitter junction,structure and fabrication characteristics of SiC LTT,the gradually doped thin n-base and gradually doped n-buffer are used to enhance the hole-transmission in n-base,compensate for the insufficient of low hole-inj ection issue in p+n emitter junction,and improve the performances of SiC LTT.The simulation results indicate that,by using gradually doped thin n-base structure,the minimum triggering light intensity and the minimum turn-on delay time of p-type SiC LTT can be reduced by 65%and 33.7%,respectively.By using 7-shaped thin n-base doping profile structure,the minimum triggering light intensity and the minimum turn-on delay time of p-type SiC LTT can be reduced by 68.3%and 50.3%,respectively.By using gradually doped n-buffer structure,the on-state voltage drop of n-type SiC LTT can be reduced by 44.9%.By using 7-shaped n-buffer doping profile structure,the on-state voltage drop of n-type SiC LTT can be reduced by 47.3%.4.The trenched-junction insulated amplifying gate is proposed.The action mechanism of trenched-junction insulated amplifying gate and characteristics of 7-shaped thin n-base doping profile SiC LTT with trenched-junction insulated amplifying gate are studied by numerical simulation.The results indicate that the trenched-junction insulated amplifying gate are more effective,in increasing device area efficiency compared to resistance-isolated amplifying gate,and in improving blocking characteristic compared to trench-isolated amplifying gate.5.The SiC LTT with double-layer thin n-base is designed and triggered by UV-LED firstly.The experimental results indicate that the on-state voltage drop of the designed SiC LTT is about 4.97V when the on-state current is 10A.The forward leakage current is lower than 20μA when the blocking voltage is around 1000V.When under 400V forward bias,the fabricated 4H-SiC LTT can be triggered on by 365nm UV light with an intensity of 100mW/cm2.The turn-on delay time and the anode voltage falling time of the fabricated LTT are less than 15μs and 110ns,respectively.