S. Heppel et al., Mode conversion in GaN based laser structures on sapphire due to the birefringence of the nitrides, PHYS ST S-A, 176(1), 1999, pp. 73-77
In this paper, we present our investigations of the waveguiding properties
of various GaInN/GaN-DH and laser structures; particularly with regard to t
he influence of the substrate. Due to the small refractive index of sapphir
e and the neccessity of a thick GaN buffer,:several higher order modes (up
to 30) are guided in a complete laser structure on sapphire. This and the f
act, that the nitrides are birefringent, lead to mode coupling phenomena. T
o support our experimental results we performed calculations with a 4 x 4 t
ransfer-matrix method, taking into account the birefringence of the materia
l. The results are in good qualitative agreement with our experimental data
.