Amorphous hydrogenated silicon nitride (a-SiNx:H) films of different compositions (0≤x≤1.18) were prepared by pulsed glow discharge plasma immersion ion implantation and deposition. The processing gases were silane and nitrogen at a substrate temperature ≤50 °C. The properties of the films were investigated using Rutherford backscattering, elastic recoil detection analysis, UV–visible optical absorption, Fourier transform infrared, and Raman spectroscopies, and nanoindentation. Depending on the value of x, the band gap of the films changes from 1.54 to 4.42 eV, and hardness changes from 11.2 to 15.3 GPa. Changes in the film properties are caused by formation of Si–N bonds and by reducing disorder in the films. It is shown that hard and transparent silicon nitride films can be obtained at room temperature.