We report on two pulse, degenerate four wave mixing (DFWM) measurements on shallow InGaN/GaN multi-quantum wells (MQWs) grown on sapphire substrates. These reveal pulse length limited signal decays. We have found a 10:1 resonant enhancement of the DFWM signal at the excitonic transition frequencies which thereby give a sharp discrimination of the discrete excitonic contributions within the featureless distribution seen in absorption spectra. The exciton resonances have peak positions, which yield good overall agreement with a full k.P model calculation for the quantum well energy levels and optical transition matrix elements. InGaN/GaN MQWs generally exhibit strongly inhomogeneously broadened excitation spectra due to indium fluctuation effects; this approach therefore affords a practical method to extract information on the excited excitonic states not available previously
@article{arxiv.1401.3156,
title = {Resolution of Discrete Excited States in InGaN Multiple Quantum Wells using Degenerate Four Wave Mixing},
author = {D. O. Kundys and J. -P. R. Wells and A. D. Andreev and S. A. Hashemizadeh and T. Wang and P. J. Parbrook and A. M. Fox and D. J. Mowbray and M. S. Skolnick},
journal= {arXiv preprint arXiv:1401.3156},
year = {2015}
}