Optical absorption of nanometer-sized band-edge-modulated amorphous silicon-nitrogen films

Optical absorption of nanometer-sized band-edge-modulated (BM) amorphous silicon-nitrogen (a-Si1-xNx:H) films, BM films, are discussed using the effective medium expression and characterized in terms of the optical gap Eg, the value of the slope in Tauc plot B, the Urbach energy Eu and the refractive index n0 as functions of the modulation period L and their correlations between them. Eg in BM film increases with decreasing L without changing n0, i.e., average composition in the film. This results in the quantum-size effect. The values of B are hardly affected by L, while Eu increases with decreasing L. The increase in Eu is not expected from the effective medium expression and attributed to the effect caused by the sinusoidal modulation of the band-edge