**6.2. N**2**O and NH**<sup>3</sup>

Ammonia (NH3) POA shows benefits as well in terms of *Dit* reduction close to the conduction band edge of 4H-SiC [39, 53, 133]. However, it yields unnecessary incorporation of nitrogen throughout the oxide, totalling a density ∼ 100 times larger than NO POA. This compromises the integrity and reliability of the gate dielectric, as evidenced by the lowering of the breakdown voltage.

Nitrous oxide (N2O) oxidation or POA also improves the properties of the oxide/semiconductor interface, but to a lesser extent than NO [12, 37, 70, 76, 81]. This is because it decomposes at high temperature into NO, O2, and N2. While the resulting NO incorporates nitrogen at the 4H-SiC/SiO2 interface, the larger fraction of background oxygen mitigates this greatly. Indeed, since incorporated N is unstable against the slow re-oxidation occurring in parallel, N2O POA yields about an order of magnitude less nitrogen than pure NO POA at similar process temperature. It reduces D*it* by about a factor of 2 close to E*c* and leads to a peak field-effect mobility of up to ≈ 25 cm2/V.s in 4H-SiC transistors, as indicated in Fig. 10. However, nitrous oxide is sometimes preferred over NO for safety reasons as it comes with less demanding handling requirements.
