Resolution of Discrete Excited States in InGaN Multiple Quantum Wells using Degenerate Four Wave Mixing


Abstract in English

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

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