Channel engineering of 4H-SiC MOSFETs using sulphur as a deep level donor

We demonstrate Si-face 4H-SiC MOSFET using sulphur (S) as a deep level donor in channel region, for the first time. Contrary to general recognition that deep level donors are not suitable for device fabrication, S is found to be a promising deep level donor for the channel region of 4H-SiC MOSFETs. Compared with channels doped by shallow level donors, S-doped channel is found to provide lower channel resistance (R ch ) and higher threshold voltage (V th ). On the basis of simulations and experiments, this improvement is found to be ascribed to two inherit natures of S in 4H-SiC. One is the large ionization energy (E ion ), resulting in the increase of V th . Another is that S act as a donor, improving inversion layer mobility in channel region. By applying this novel channel engineering to vertical 4H-SiC MOSFETs, 31% reduction of specific on resistance (Ron) at high V th of 4.0 V was achieved.