Extremely large refractive index of strained GaInNAs thin films

The refractive index of-strained GaInNAs layers was investigated. By spectroscopic ellipsometry (SE), changes in the optical constants of GaInNAs layers could be observed clearly, even though the layers were as thin as 6 nm and the nitrogen content was less than 1%. The refractive index of GaInNAs was found by ellipsometric analysis to increase in proportion to the nitrogen content taking the layer strain into account. The increase in the refractive index as the bandgap energy decreased was consistent with that observed in conventional III-V alloy semiconductors. The rate of increase relative to the bandgap shrinkage was, however, more than triple that in GaInAs. This may be due to the high density of states in the conduction band, which is unique to this type of material system that includes nitrogen atoms.