Origin of thermal quenching of exciton photoluminescence in AlGaN epilayers

Dynamics of a low-density exciton system is simulated using the kinetic Monte Carlo algorithm. The temperature dependences of photoluminescence (PL) intensity and PL band Stokes shift in a high-Al-content AlGaN epi­layer are calculated and fitted to the experimentally measured ones. The key features of nonradiative recombination via delocalized states and direct tunnelling to nonradiative recombination centres and their influence on PL efficiency are analysed. A strong influence of the tunnelling-based recombination in AlGaN epilayers with a large ratio between the densities of nonradiative recombination centres and localized states is revealed.

Exciton–Exciton Interactions in Coaxial Double Quantum Rings

We study theoretically the quantum states of two interacting excitons in coaxial double quantum rings. An interplay between exciton–exciton Coulomb interactions and specific geometry of the structure leads to the emergence of peculiar energy spectrum of two exciton system. We develop a semi-analytic approach providing highly accurate energies of system in the wide range of values of geometrical parameters relevant to experimental realizations.

Coherent potential approximation for the absorption spectra of a two-dimensional Frenkel exciton system with Gaussian diagonal disorder

We investigate the optical absorption and the density of states of a Frenkel exciton system on a square lattice with nearest-neighbor interactions and a Gaussian distribution of transition frequencies (i.e. Gaussian diagonal disorder). Results are presented for the absorption and the density of states of direct and indirect edge systems for a range of variances. There is reasonable agreement with the corresponding finite array calculations of Schreiber and Toyozawa. The existence of an Urbach tail is also investigated.