Anatomy of internal electric field profile in operating SiC power MOSFETs with local contact potential probing

Abstract

A comprehensive understanding of local contact potential profiles and carrier transport mechanisms in SiC MOSFETs is crucial for optimizing device design and performance. We report the evolution of local contact potential across the cross section of 1200 V SiC MOSFETs under applied external bias using Kelvin probe force microscopy. In the vertical direction of the cross section, notable features in the relative contact potential difference (RCPD) are identified at the interfaces of the P well and N− drift layer, as well as between the N− drift layer and the N+ substrate. The RCPD drop-out values at the P well to N− drift layer interface increase from 0.17 to 1.54 V and then to 2.94 V as the external voltage is adjusted, with corresponding values of 2.43 and 3.86 V observed at VGS = VDS of 2 and 4 V, respectively. Conversely, the RCPD drop values at the N− drift layer to N+ substrate interface fluctuate between −0.38 and 0.74 V. In the horizontal direction of the cross section, as VGS = VDS increases from 0 to 4 V, the RCPD drop-out values change from 0.14 to 1.33 V, and ultimately reach 2.41 V. These variations are indicative of enhanced energy band bending at the P–N junction due to charge injection, revealing key insights into the electric field distribution within the device. This study elucidates the local contact potential profile evolution in SiC MOSFETs and highlights intrinsic electrical properties essential for advancing SiC-based power devices.