Dynamics of localized excitons in InGaN/GaN quantum wells

By using a "nanoscale aperture" method, we studied the dynamics of localized excitons in active InGaN layers in an InGaN/GaN multiple quantum well (MQW). Local photoluminescence (PL) from local excitation shows very different characteristics from far-field luminescence. PL spectra from these nanoapertures are, in general, blueshifted relative to the spectra acquired in the unmasked regions. The spectra vary from aperture to aperture, reflecting the spatial fluctuation of the In composition in the MQW. In addition, one typically observes spectra with clearly resolved multiple peaks from the small apertures, which may be attributed to compositional and size fluctuations over a length scale longer than the exciton diameter but smaller than the aperture size. The excitation intensity dependence of PL indicates a band-filling effect in the multiple-peak structure. Finally, time-resolved studies reveal a very interesting spectral weight shifting between the higher energy peaks and the lower-energy peaks.