Study On Minority Carrier Lifetime Of 4H-SiC PiN Diodes

Minority carrier lifetime is considered to play a very important role in the characteristics of PiN diodes, such as turn-on voltage and switching time. Control technology of minority carrier lifetime can effectively reduce the switching time and the peak reverse current of 4H-SiC PiN diode, and improve switch characteristics of device. There are few reports about the influence of the local lifetime control technique using electron irradiation on 4H-SiC PiN diodes. This thesis presents some work on those results in concern.Numerical model has been setup with right parameters for 4H-SiC PiN. The DC I-V characteristics and switching characteristics are simulated accurately by ISE-TCAD. The influence of minority carrier lifetime on forward characteristics and switching characteristics are simulated. With shorter minority carrier lifetime, the turn-on voltage increases while the switching time decreases.Electron irradiation can reduce materials'minority carrier lifetime and improve switching characteristics of devices, but it also cause the degradation of the forward characteristics. Through the Cu mask between the device and the irradiation source, we can control the Z1/2 (and EH6/7) concentration by low-energy electron irradiation. Some work has been done on the dc and reverse recovery characteristics of 4H-SiC PiN diodes after local electron irradiation. At room temperature, when the diode is switched from forward-biased at 3.1 volts to a reverse bias of 50 volts, the turn-off time is only 50 nanoseconds while the peak reverse current is 3.5×10^-4amper,which show significantly reduce compared with the data before local irradiation ,70 nanoseconds and 8.5×10^-4 ampere. Unlike the significantly increase of the turn-on voltage after nonlocal electron irradiation, the turn-on voltage after local electron irradiation only shows slight increase.Local electron irradiation aiming on intentional local lifetime reduction in drift region enables control of the charge gradient profile. Local lifetime control achieves the tradeoff between low forward voltage and short recovery time, and improves the devices'characteristics.