Characterization of the refractive index of strained GaInNAs layers by spectroscopic ellipsometry

We have characterized the refractive index of strained GaInNAs layers. Using spectroscopic ellipsometry (SE), the variation in optical constants of GaInNAs layers, about 6 nm thick with a nitrogen content lower than 1%, can be clearly observed. Analysis of the SE data, including the strain effect in the layer, clarified that the refractive index of GaInNAs increases in proportion to the nitrogen content. While the trend for increase in refractive index with a decrease in the bandgap energy is the same as that observed in conventional III-V alloy semiconductors, the rate of increase is found to be much larger than that in GaInAs. This result suggests a large density of states in the conduction band characteristics of this type of material system that includes nitrogen atoms.