Dynamics of nonequilibrium carrier decay in AlGaN epitaxial layers with high aluminum content.

Carrier dynamics in high-Al-content AlGaN epilayers with different dislocation densities from 5 × 10(8) cm(-2) to 5 × 10(9) cm(-2) is studied by comparing the photoluminescence decay with the decay of carrier density. The carrier density decay was investigated using the light-induced transient grating technique. This comparison shows that the luminescence at the nonequilibrium carrier densities expected in operating light-emitting diodes depends on the recombination of free carriers and the localized exciton-like electron-hole pairs and localization-delocalization processes. In addition, a fraction of the nonequilibrium carriers is captured by the deep capture centers with extremely long lifetimes. These carriers have an insignificant contribution to the band-to-band radiative recombination. This capture is an important factor in decreasing the emission efficiency.