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].