The spectral dependences of the nonequilibrium carrier lifetimes obtained by using time-resolved photoluminescence (PL) spectroscopy reveal new features in the carrier dynamics in AlGaN epilayers with high aluminum content. Three decay components can be traced in the PL decay. The fast, intermediate, and slow components are attributed to the decay of the free carriers, localized carriers, and the carriers trapped in deep states, respectively. The spectral dependence of the fast component is flat with a very weak dependence on temperature. At low temperatures, the intermediate decay component has the longest effective decay times in the vicinity of the PL band peak and exhibits a decrease on both high and low energy slopes. The spectral dependence of the lifetimes flattens at elevated temperatures. To interpret the decrease in the carrier lifetime at lower energies, we suggest the modification of the double-scaled potential profile in AlGaN alloys by introducing a gradual potential decrease to the low-potential regions instead of the abrupt walls of the regions previously assumed.

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.

Krūvininkų dinamikos III grupės nitriduose modeliavimas kinetiniu Monte Karlo metodu

A model for the dynamics of a coupled system of free and localized carriers in semiconductors with strong carrier localization is suggested. Kinetic Monte Carlo technique is exploited for simulations. The model is verified by fitting the simulated and experimental temperature dependences of photoluminescence (PL) band intensity, peak position, and band width, and the carrier density dependence of PL efficiency in AlGaN quantum wells. The influence of carrier localization conditions on the dominating carrier migration and recombination processes is revealed. The efficiency droop effect is shown to be caused by peculiarities of carrier localization without significant influence of Auger recombination.