Critical spatial disorder in InGaN resonant Bragg structures

We study a disorder-induced transformation of the resonant optical reflection from a nearly periodic system of quasi-2D excitons in the InGaN quantum wells arranged as a resonant Bragg structure (RBS). We show that there is a critical deviation from the exact periodicity when the reflection by a single super-radiant exciton–polariton mode is transformed into a multimode spectrum. This critical disorder appears to be inversely proportional to the number of periods in the RBS. Using a numerical model which describes the experimentally observed optical spectra, we found the critical standard deviation from exact periodicity to be 1.76%, 1.0%, and 0.45% for InGaN-based RBS with 60, 100, and 200 periods, respectively.