Modelling the interactions and diffusion of NO in amorphous SiO2

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 binds at the network sites with wide O–Si–O bond angles, which also serve as the intrinsic precursor sites for electron trapping.