Exciton recombination dynamics in a -plane (Al,Ga)N/GaN quantum wells probed by picosecond photo and cathodoluminescence a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence ͑PL͒ reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature ͑9 K͒ time-resolved PL ͑TRPL͒ study shows that the sample

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... th 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy E loc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.