Field-plate design for edge termination in silicon carbide high-power Schottky diodes

Abstract

Theoretical two-dimensional simulations have been performed using the ATLAS device simulator from Silvaco (Santa Clara, CA) to investigate the influence of field plate on the high-power performance of n-type 4H-silicon carbide (SiC) Schottky diodes. For the simulations, the doping level of the substrate, the permittivity of the dielectric layer, the thickness of the dielectric layer, the length of the field plate, and the thickness of the field plate have been critically analyzed. The peak electric fields both at the edge of the field plate and inside the dielectric layer have been calculated. The dependence of the junction breakdown voltage on the substrate doping level, the diode temperature, the dielectric layer thickness, and the permittivity of the dielectric layer has been examined. Theoretical simulations have been compared with available experiments, which lend support to the validity of the present results. It has been observed that only a combined impact of optimization of various parameters can lead to the best improvements in field-plated diodes. The optimized overlap between the Schottky-metal contact and the field plate underneath this contact has particularly been found very important. Also, the dielectric layer thickness should neither be very small nor very large, and the doping concentration should preferably be around ND=1×1015 cm−3. A small dielectric layer thickness generates a very large electric field. On the other hand, a large dielectric layer thickness exhibits a very high impact ionization potential. The newest and perhaps the most exciting finding of this investigation is a novel structure exhibiting composite dielectric deposited on the SiC substrate and a second dielectric covering the field-plate edge.