Study of MBE-grown GaN/AlGaN quantum well structures by two wavelength excited photoluminescence

We report experimental results of two wavelength excited photoluminescence (TWEPL) applied to GaN/Al0.2Ga0.8N multiple quantum well structures grown b y plasma assisted molecular beam epitaxy. An increase or a decrease in phot oluminescence (PL) indicate the presence of trap centers with dissimilar ch aracteristics for each case. In these samples, a spatial inhomogeneity of t rap distribution originating from the growth process was detected due to di fferent change in PL for distinct regions. Also a time-dependent phenomenon in PL was observed: after a continuous midterm irradiation with UV light ( 4.12 eV), the amount of change in FL, which is characteristic of TWEPL, bec ame nil. We argue this phenomenon is a complex issue that can be due to mig ration of native defects or a kind of saturation process involving trap cen ters.