Analysis of trapping effects on the forward current-voltage characteristics of al-implanted 4H-SiC p-i-n Diodes

The forward current-voltage characteristics (IF-VF) of aluminum (Al) implanted 4H-SiC p-i-n diodes are investigated by means of a numerical simulation study that takes into account both intrinsic and doping-induced deep-defects, namely the Z1/2 and EH6/7 centers inside the drift region and an electrically active trap concentration inside the anode region due to the Al+ ion implantation process. From the experimental results, the fundamental electric parameters of several samples were extracted at different regions of diode operation and used for comparison. The modelling analysis reveals that Z1/2 and EH6/7 centers reduce the effective carrier lifetimes and increases the recombination rate in the drift region determining the slope of the IF curve in the recombination and diffusion regimes. In addition, a defect density that becomes comparable to the epilayer doping concentration introduces an apparent shunt resistance effect at low-medium biases and at the same time has a noticeable impact on the diode series resistance at voltages higher than 2.7 V. A detrimental effect on the series resistance is also observed in dependence of the trap concentration in the anode region that increases the diode internal resistance as a consequence of the carrier mobility decrease. Above the IF curve knee the diode current is largely dominated by the electron injection into the anode since the concentration of free holes for conduction is strongly limited in turn by the incomplete activation of the ion implanted impurities and the trap activity.