Modelling the interactions and diffusion of NO in amorphous SiO2

Abstract

Abstract Nitric oxide (NO) is often used for the passivation of SiC/SiO2 metal oxide semiconductor (MOS) devices. Although it is established experimentally, using XPS, EELS, and SIMS measurements, that the 4H-SiC/SiO2 interface is extensively nitridated, the mechanisms of NO incorporation and diffusion in amorphous (a)-SiO2 films are still poorly understood. We used density functional theory (DFT) to simulate the incorporation and diffusion of NO through a-SiO2 and correlate local steric environment in amorphous network to interstitial NO (NO i ) incorporation energy and migration barriers. Shapes and volumes of structural cages in amorphous structures are characterised using a methodology based on the Voronoi S-network. Using an efficient sampling technique we identify the energy minima and transition states for neutral and negatively charged NO i molecules. Neutral NO i interacts with the amorphous network only weakly with the smallest incorporation energies in bigger cages. On the other hand N O i − 1 binds at the network sites with wide O–Si–O bond angles, which also serve as the intrinsic precursor sites for electron trapping.