Several series of amorphous silicon nitride thin films have been grown by plasma-enhanced chemical vapour deposition, where the ratio of ammonia and silane feed gases was held constant for each series while the deposition temperature was varied from 160 °C to 550 °C, and all other deposition conditions were held constant. Photothermal Deflection Spectroscopy measurements were used to determine the Urbach slope E0 and the defect density ND. It is found that ND is determined by E0 for most of these samples, suggesting that defect equilibration occurs in a-SiNx:H for x up to at least 0.6. The growth temperature at which the disorder is minimised increases to higher values with increasing x, which is explained in terms of a hydrogen-mediated bond equilibration reaction. Fourier Transform Infra Red spectroscopy measurements were performed to determine the changes in hydrogen bonding with growth temperature. The results suggest that a second bond equilibration reaction also occurs at the growing surface, but that equilibrium cannot be reached at higher temperatures because of hydrogen evolution from Si-H bonds.