Near-field microscopy on GaInN/GaN green light emitting quantum-well structures

In contrast to blue emitting GaInN/GaN quantum well structures, which show a quite high internal quantum efficiency (IQE), the IQE of green emitting GaInN/GaN quantum well structures is dropping quickly towards longer wavelengths. Another difference between blue and green quantum wells is the fact that the effect of thermal annealing on the luminescence is much stronger for the structures emitting in the green. In this contribution we will present spatially resolved photoluminescence measurements on structures emitting in the blue and green respectively, before and after a thermal annealing process to further investigate the inferior performance of green-emitting structures. The measurements were done with a scanning near-field optical microscope (SNOM) with which we are able to investigate the luminescence structure with a spatial resolution far below the diffraction limit (∼50 nm).