Deep ultraviolet luminescence and charge-transfer excitons in atomically thin GaN quantum wells*

We investigate the electronic, excitonic, and optical properties of atomically thin GaN quantum wells embedded in AlN or AlGaN barriers using first-principles calculations based on density functional theory (DFT) and many-body perturbation theory. The strong quantum confinement results in deep ultraviolet luminescence. Also, the quasi-2D structural characteristic produces strongly bound excitons, which are even stable at room temperature. We also investigate the properties of pairs of atomically thin GaN wells, separated by polar AlN barriers. The perpendicular electrical polarization produces charge-transfer excitons, in which electrons and holes are spatially separated in the two different GaN wells. Compared to direct excitons, the reduced overlap of charge-transfer excitons enables exciton lifetime that are 3-4 orders of magnitude longer. By adjusting the separation distance between electrons and holes through variations of the well and barrier thickness we can control the exciton lifetime and the binding energy simultaneously.