Influence of ${\text{Si}}_3{\text{N}}_4$ layer on the electrical properties of Au/n-4H SiC diodes

In this study, the effect of ${\text{Si}}_3{\text{N}}_4$ insulator layer on the electrical characteristics of Au/n-4H SiC diode was investigated. The current–voltage ($I-V$), capacitance–voltage ($C-V$) and conductance–voltage ($G/w-V$) measurements were carried out at room temperature condition. Under thermionic emission model, electrical parameters as zero-bias barrier height (${\Phi }_{Bo}$), ideality factor (n), interface states ($D_{it}$), and series ($R_s$) and shunt ($R_{sh}$) resistances were estimated from forward bias $I-V$ analyses. The values of n and ${\Phi }_{Bo}$ were about 1.305 and 0.796 eV for metal–semiconductor (MS) rectifying diode, and 3.142 and 0.713 eV for metal–insulator–semiconductor (MIS) diode with the insertion of ${\text{Si}}_3{\text{N}}_4$ layer, respectively. Since the values of n were greater than the unity, the fabricated diodes showed non-ideal $I-V$ behaviour. The energy distribution profile of $D_{it}$ of the diodes was calculated by taking into account of the bias dependence of the effective barrier height (${\Phi }_e$) and $R_s$. The obtained $D_{it}$ values with $R_s$ are almost one order of magnitude lower than those without $R_s$ for two diodes. According to Cheung's model, $R_s$ were calculated and these values were found in increasing behaviour with the contribution of ${\text{Si}}_3{\text{N}}_4$ insulator layer. In addition, the $J_R-V$ plot behaviours with linear dependence between ln($J_R$) vs.$V^{0.5}$ indicated that the dominant conduction mechanism in the reverse bias region was Schottky effect for both MS and MIS diodes. In the room temperature $C-V$ measurements, different from the results of MIS diode, the values of C for MS diode was observed in decreasing behaviour from ideality with crossing the certain forward bias voltage point ($\sim$$2.5\text{V}$). The decrease in the negative capacitance corresponds to the increase of G / w.