Detailed investigation of n-channel enhancement 6H-SiC MOSFETs

Basic MOSFET parameters like inversion layer mobility, threshold voltage, intrinsic mobility reduction factor and interface state density extracted from the subthreshold slope were examined in detail for 6H-SiC enhancement-mode n-channel MOSFETs. The inversion layer mobility and the threshold voltage were determined as a function of substrate doping concentration as well as device temperature. The interface state density was studied for different substrate doping concentrations. The inversion layer mobility was found to decrease strongly with increasing substrate doping. In contrast to earlier reports the inversion layer mobility decreases also with temperature. Furthermore, the threshold voltage depends more pronounced on substrate doping and temperature than theoretically expected. The interface state density extracted from the subthreshold slope increases significantly with substrate doping concentration. All these phenomena are consistently interpreted by the classical MOSFET behavior which is extended by acceptor like interface states. These states are located close to the conduction band and exhibit a density increasing drastically toward the band edge.