Assessment and Modification of Recombination Dynamics in In_xGa_1-xN-Based Quantum Wells

Nanoscopic optical characterization using scanning near-field optical microscopy was performed on both InxGa1-xN/GaN single quantum wells (SQWs) grown on polar (0001) orientation and a semipolar (1122) microfacet SQW fabricated by a re-growth technique. The photoluminescence intensity of a conventional (0001) SQW emitting in the blue was completely independent of the threading dislocations (TDs) due to the small diffusion length less than 100 nm. In contrast, the photoluminescence intensity was well correlated with the TDs in the sample emitting in the green due to the association of In-rich clusters with dislocations, and the effect was enhanced by the larger diffusion length contribution from the longer radiative recombination lifetime. It was found that in a (1122) SQW, the suppression of the piezoelectric field leads to orders-of-magnitude faster radiative lifetime and consequently, a shorter diffusion length. In addition, the highest internal quantum efficiency was approximately 50% at 520 nm, which is about 50 nm longer than in (0001) QWs, suggesting that (1122) QWs are suitable for green emitters.