Recombination and Excess Currents in 4H-SiC Structure with Low-Doped n-Region

Presented in this paper are the results of a study of forward and reverse current-voltage characteristics of the 4H-SiC pn structures produced by implantation of Al+ ions in low-doped ((5-7)∙1014cm-3) n-type conductivity epitaxial layer. A forward current was identified which is consistent with the model of recombination in the space charge region of a pn junction via a deep level: J=Joexp(qU/nkT), where Jo=Jo*exp[-Ea/(kT)] (or J= Jo*exp[(qU-2Ea)/nkT)]) with the ideality factor n=2. Parameters of this current are as follows: Jo(293 K) ~ 8∙10-25 A/cm2, Ea 1.73-1.75 eV (2Ea3.46-3.5 eV), Jo*~7∙105 A/cm2. A comparison of the experimental and model-based values of Ea, with allowance for all clearly defined temperature dependences, both strong and weak, of the model of recombination in the space charge region shows that the effective lifetime increases and effective trapping cross section σeff of the recombination level decreases with increasing temperature: σeff ~ T-2÷σeff ~ T-2.5 or σeff ~exp(ΔE /kT) where ΔE=80-100 meV. Reverse current practically in whole temperature range is excess current, only at high temperatures (~800 K) reverse current became close to generation current in space charge region. Special interest are the excess currents as a result of the application of a reverse or forward voltage at high temperature. The barrier type excess currents is characteristic of SiC.