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

Abstract

Strain relaxation effect by nanotexturing InGaN/GaN multiple quantum wellEffects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor depositionThe optical properties of InGaN/GaN quantum wells, which were nanopatterned into cylindrical shapes with diameters of 2 m, 1 m, or 500 nm by chemically assisted ion beam etching, were investigated. Photoluminescence ͑PL͒ 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.

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

“…This value agrees well with the results shown in Ref. 10. Furthermore, compared with the previous fluorescence microscope images, our high resolution CL hyperspectral imaging reveals a much more detailed emission wavelength distribution in these micro-pillars and thus enables us to investigate the local strain relaxations.…”

“…15 However, in choosing boundary conditions, previous authors have usually just considered the local environment of the QWs while neglecting the influence from other layers. 9,10,13,15 This assumption becomes increasingly inaccurate when the fill factor of etched mesas (the ratio of mesa area to total sample area) is very small and the height of the mesa is relatively large. Moreover, the spatial resolution of the photoluminescence measurements used so far was limited by the size of the beam spot.…”

“…V C 2012 American Institute of Physics 112, 013107-1 800 nm at 4.2 K. 10 With such resolutions, it is not possible to investigate the detailed strain relaxation process at a submicron scale and direct comparison between the experimental and simulation results is also hard to achieve. Clearly, further improvement of spatial resolution and simulation accuracy will enable a much better understanding of the mechanism of strain relaxation in the micro-GaN pillars, which is critically important to the design of novel micro/nano pixellated LED devices for a wide range of applications.…”

“…[3][4][5][6][7][8][9][10][11][12] The fabrication method has typically involved "top-down" patterning by etching an initially planar epitaxial structure containing InGaN/GaN QWs, although studies of directly grown nano-columnar structures have also been reported. 12 Correlations between spectroscopic results and numerical simulations of strain relaxation in the QWs were included in the reports by Yu et al 9 and Kawakami et al 10 The authors of Ref. 9 employed an atomistic valence force field (VFF) method for strain calculations.…”

“…Meanwhile in Ref. 10, the finite element method (FEM), embodying macroscopic elastic theory, was used. Analogous FEM calculations have proved effective in simulating semiconductor nanostructures including self-organized GaN/AlN quantum dots, 13 InAs quantum dots 14 and nanocolumnar GaN/AlGaN disks.…”