Theoretical modeling on hydrogen evolution in ultraviolet light-treated hydrogenated silicon nitride

Ultraviolet light illumination is shown experimentally to be able to induce hydrogen evolution in hydrogenated amorphous silicon nitride (a-Si_xN_yH_z) film and the total hydrogen (H) removal percentage depends strongly on the composition with a maximum with balanced silicon-hydrogen and nitride-hydrogen single bonds (Si–H/N–H ratio equals to 1). We developed a general model for analyzing H removal in such alloyed glass system. Our statistical Monte Carlo models reveal that H₂ evolution is the result of highly selective chemical reactions among nearest neighbor SiH and NH bonds in a-SiN_xH_y, which leads to formation of Si–N bonds. This process is sensitive to its local chemical environment. The nearest neighbor coordination number and the presence of SiH₂ and NH₂ groups in a-Si_xN_yH_z network have impact on the total H removal. Our model gives quantitative measures for all the corresponding reaction constants, consistent with experimental observations.