Optical properties of InGaN/GaN nanopillars fabricated by postgrowth chemically assisted ion beam etching

The optical properties of InGaN/GaN quantum wells, which were nanopatterned into cylindrical shapes with diameters of 2 μm, 1 μm, or 500 nm by chemically assisted ion beam etching, were investigated. Photoluminescence (PL) and time-resolved PL measurements suggest inhomogeneous relaxation of the lattice-mismatch induced strain in the InGaN layers. By comparing to a strain distribution simulation, we found that partial stain relaxation occurs at the free side wall, but strain remains in the middle of the pillar structures. The strain relaxation leads to an enhanced radiative recombination rate by a factor of 4–8. On the other hand, nonradiative recombination processes are not strongly affected, even by postgrowth etching. Those characteristics are clearly reflected in the doughnut-shape emission patterns observed by optical microscopy.