Persistent relaxation processes in proton-irradiated 4H-SiC

The processes of long-term (persistent) conductivity relaxation in $n$-type silicon carbide irradiated with protons in a wide range irradiation temperatures $T_i$ from 23 to 500$^\circ$C are studied. It is shown for the first time that as a result of the proton irradiation with the fluence of 10$^{14}$ cm$^{-2}$, two “competing” long-term processes of conductivity relaxation can be observed. The characteristics of both processes significantly depend on the irradiation temperature and bias, at which the dynamics of conductivity changes is studied. After applying a relatively small constant voltage to the sample, the decrease in current during persistent relaxation process is replaced by persistent increase in current and establishing of the steady state. Both processes are characterized by a very wide range of time constants. When irradiation is performed at room temperature ($T_i$ = 23$^\circ$C), the time constants range from milliseconds to hundreds of seconds. When the samples are irradiated at elevated temperatures, the time constants are in the range from milliseconds to hundreds of milliseconds. The higher the bias applied, the faster the decrease in current is replaced by its increase. The possible nature of the observed effects is discussed.