Ideal 4H-SiC pn junction and its characteristic shunt

The results of a study of forward current–voltage characteristics of 4H-SiC pn structures produced by various methods are presented in this paper. In all pn structure types a forward current was identified which is consistent with the model of recombination in the space charge region via a deep level: J=Jo exp(qU/nkT), where Jo=Jo* exp[−Ea/(kT)] (or J=Jo* exp[(qU−2Ea)/nkT)]) with the ideality factor n=2. The values of the other parameters are as follows: Jo(293 K)∼(10−24–10−25) A cm−2, Ea≈1.75 eV, Jo*∼(105–106) A cm−2. In the absence of other leaks, this current represents a natural (intrinsic) shunt for the diffusion current at low biases and determines the value of the injection coefficient of a pn junction. In many of the pn structures the forward current, while showing an exponential dependence on voltage and temperature, was significantly higher than the current described above. The ideality factor, in some instances, was close to unity. A situation with such characteristics can be considered as an ideal extrinsic (due to nonuniformities) barrier type shunt. The potential barrier height of this shunt is ≈1.4 eV. This sort of shunt is characteristic of SiC; earlier a similar object, presumably of the same origin, was identified in 6H-SiC pn structures.