Two-Dimensional Excitons in Multiple GaN/AlN Monolayer Quantum Wells

The decay kinetics of low-temperature exciton photoluminescence in a heterostructure with multiple GaN/AlN monolayer quantum wells, which is prepared by molecular beam epitaxy, is studied. Measured radiation decay curves are theoretically simulated within a three-level model. The relaxation of dipole-allowed "bright" excitons spatially confined in GaN monolayers is determined as exciton relaxation with a characteristic time of ~3 ps, which is accompanied by spin flip and by transformation to dipole-forbidden "dark" excitons whose levels lie by ~60 meV below in energy. It has been shown that exciton states at temperatures above 50 K are two-dimensional.