InGaN is the key compound of the state-of-the-art blue-UV light emitting diodes and laser diodes. InGaN layers have inherent compositional fluctuations resulting in potential fluctuations, which localize carriers/excitons so that their nonradiative recombination is inhibited and light emission efficiency is increased. However, such an inherent disorder obscures the absorption edge of InGaN, which is a fundamental optical property.
In this report we apply photoluminescence (PL), PL excitation, and photoreflectance spectroscopy to characterize the absorption edge of InGaN multiple quantum wells with different In content (20-30%) and propose Monte Carlo simulation of exciton hopping to quantitatively describe band-edge dynamics in the temperature range of 10-300 K and to estimate the scales of potential fluctuations in the alloy.
The simulation yielded a temperature dependence of the Stokes shift between the PL peak and the average exciton position as well as of the PL linewidth. We described quantitatively the experimental data by introducing a double-scale potential profile. One potential fluctuations scale reflects formation of In-rich regions with different average In content, while another scale corresponds to the variations of local indium content within a single In-rich region. Moreover, the Monte Carlo approach enabled us to estimate the band edge energy in the entire temperature range. The determined band edge was found to correspond to that obtained from the photoreflectance measurements within the experimental uncertainty. Increased indium content in InGaN alloy resulted in an increase of the both scales of potential fluctuations.