An investigation was conducted into the effect of hydrogen dilution on the mi-crostructure and optical properties of silicon nanograins embedded in silicon nitride (Si/SiNx)thin film deposited by the helicon wave plasma-enhanced chemical vapour deposition technique.With Ar-diluted SiH_4 and N_2 as the reactant gas sources in the fabrication of thin film,the filmwas formed at a high deposition rate.There was a high density of defect at the amorphous silicon(a-Si)/SiN_x interface and a relative low optical gap in the film.An addition of hydrogen into thereactant gas reduced the film deposition rate sharply.The silicon nanograins in the SiN_x matrixwere in a crystalline state,and the density of defects at the silicon nanocrystals (nc-Si)/SiN_x inter-face decreased significantly and the optical gap of the films widened.These results suggested thathydrogen activated by the plasma could not only eliminate in the defects between the interfaceof silicon nanograins and SiNx matrix,but also helped the nanograins transform from the amor-phous into crystalline state.By changing the hydrogen dilution ratio in the reactant gas sources,a tunable band gap from 1.87 eV to 3.32 eV was obtained in the Si/SiN_x film.
