  We present a comprehensive tensorial characterization of second-harmonic
generation from silicon nitride films with varying composition. The samples
were fabricated using plasma-enhanced chemical vapor deposition, and the
material composition was varied by the reactive gas mixture in the process. We
found a six-fold enhancement between the lowest and highest second-order
susceptibility, with the highest value of approximately 5 pm/V from the most
silicon-rich sample. Moreover, the optical losses were found to be sufficiently
small (below 6 dB/cm) for applications. The tensorial results show that all
samples retain in-plane isotropy independent of silicon content, highlighting
the controllability of the fabrication process.
