The deposition process of passivation layer for GaN-LEDs can affect the optical and electric properties of these devices. In this paper, we use an ammonia-free process to deposit the silicon oxynitride film at low temperature (100 degrees C) through plasma enhanced chemical vapor deposition (PECVD) to serve as the passivation layer of GaN-LEDs, investigating the relationship between the refractive index of silicon oxynitride film and the light output of GaN-LEDs, and furthermore, analyzing the properties of the devices before and after the passivation. It is found that the film with the refractive index of 1.54 possesses good characteristics and the optical and electrical properties of GaN-LEDs improve greatly after the deposition of the layer. Compared with the optical and electrical properties of GaN-LEDs without a passivation layer, the light output can be increased by as high as 17.8% after the deposition of the silicon oxynitride passivation layer; the forward voltage decreased and the reverse leakage current reduced obviously. The deposition process can greatly improve the optical and electric characteristics of GaN-LEDs. (c) 2006 Elsevier Ltd. All rights reserved.