Thin-film-induced index change and channel waveguiding in epitaxial GaN films

We report on optical waveguiding in the channel region of an epitaxial GaN film defined by a SiN cladding layer of a stripe window pattern. We carried out numerical analyses on the various possible effects that might contribu te to the overcompensation of the negative loading effect of a SiN cladding window. This includes the photoelastic, piezoelectric, and electro-optic e ffects in GaN induced by a SiN window layer. The analysis result suggests t hat the observed phenomenon can be ascribed to a combination of both the ph otoelastic and electro-optic effects, and especially that the spontaneous p olarization field in undoped GaN with a low background carrier concentratio n might play an important role in forming a channel waveguide in the window region. (C) 2000 American Institute of Physics. [S0003-6951(00)02038-6].