MOSFETs (metal-oxide-semiconductor field effect transistors) fabricated with the 4H polytype of SiC have the potential for significantly improved performance compared to Si devices for high-power and high-frequency operation. However, the development of 4H MOSFETs has been hindered by unexpectedly low inversion channel mobilities—often no more than single-digit values. A few years ago Schorner, et al. (EDL 20[5]: 241, 1999) suggested that the cause for this low mobility was an asymmetric distribution of interface states in the 4H-SiC bandgap, with much higher defect densities near the conduction band edge. These band-edge states are responsible for the low-channel mobility in 4H MOSFETs because they trap and scatter charge carriers (electrons). Low mobility means low current carrying capability and therefore low power handling capability. Our paper describes a nitrogen-based technique (NO passivation) that can be used to reduce the band-edge defect state density by more than one order of magnitude and increase electron channel mobility by factors of 20-30.

The 4H polytype is the polytype of choice for SiC high-power devices, and the NO passivation process is useful for anyone in the community who wishes to fabricate 4H-SiC MOSFETs. Also this technique can be used for the SiC device passivation to get a better reliability.

Historical knowledge of the role of nitrogen in Si-based MOS device fabrication and the early papers of Hui-feng Li, S. Dimitrijev, H.B. Harrison, and D. Sweatman from Griffith University in Australia.

The MOSFET is one of the most commonly manufactured electronic devices on earth, and these transistors are used to switch electric current on and off at some voltage that is applied to the MOSFET. The power-handling capability of the MOSFET is basically the product of the current through the device and the voltage applied to it. During operation, current (in the form of electrons) flows in the semiconductor immediately adjacent to the interface between the thin oxide layer and the semiconductor. The NO (nitric oxide) passivation process places nitrogen at this interface where the nitrogen passivates defects (i.e., interface states) and prevents these defects from trapping and scattering the flowing electrons. The result is a more efficient flow of electrons that results in much higher current through the device.