Facet recovery and light emission from GaN/InGaN/GaN core-shell structures grown by metal organic vapour phase epitaxy on etched GaN nanorod arrays

Abstract

The use of etched nanorods from a planar template as a growth scaffold for a highly regular GaN/InGaN/GaN core-shell structure is demonstrated. The recovery of m-plane non-polar facets from etched high-aspect-ratio GaN nanorods is studied with and without the introduction of a hydrogen silsesquioxane passivation layer at the bottom of the etched nanorod arrays. This layer successfully prevented c-plane growth between the nanorods, resulting in vertical nanorod sidewalls (∼89.8°) and a more regular height distribution than re-growth on unpassivated nanorods. The height variation on passivated nanorods is solely determined by the uniformity of nanorod diameter, which degrades with increased growth duration. Facet-dependent indium incorporation of GaN/InGaN/GaN core-shell layers regrown onto the etched nanorods is observed by high-resolution cathodoluminescence imaging. Sharp features corresponding to diffracted wave-guide modes in angle-resolved photoluminescence measurements are evidence of the uniformity of the full core-shell structure grown on ordered etched nanorods

Investigation of indium gallium nitride facet-dependent nonpolar growth rates and composition for core–shell light-emitting diodes

“…1(b). In this work, for the subsequent InGaN layer growth, the reactor parameters rather than the NR spacing 17 determine the relative facet growth rates and the InN fraction incorporation on the respective facets. The TMIn and TMGa flows were kept constant across all the InGaN growths at 200 and 9 sccm, respectively.…”

“…Such NRs can be grown using either a bottom-up approach using selective area epitaxy [8][9][10][11][12][13][14] or a top-down approach 15,16 in which NRs with controlled aspect ratio are etched from a planar film before the regrowth of GaN/InGaN shell layers over the NRs. 4,16,17 Irrespective of their method of formation, there is substantial evidence that GaN NRs are strain-free once their height exceeds their diameter. 17,18 Therefore, the only strain in the core-shell structures described here will be due to lattice mismatch between InGaN and relaxed GaN.…”

“…4,16,17 Irrespective of their method of formation, there is substantial evidence that GaN NRs are strain-free once their height exceeds their diameter. 17,18 Therefore, the only strain in the core-shell structures described here will be due to lattice mismatch between InGaN and relaxed GaN. A particular advantage of the top-down approach lies in its potential to be highly uniform on a wafer scale.…”

“…15,18,19 In contrast to planar layer growth, uniform InGaN growth on NRs is difficult because the three-dimensional (3-D) growth mode leads to facet-dependent growth rates and indium nitride (InN) incorporation, leading to emission at multiple peak wavelengths. 4,5,17,20 Further, InGaN growth on pre-etched GaN NRs can be nonuniform for closely packed arrays, 12,21 indicating a likely dependence of indium mole fraction incorporation on NR height and spacing.…”

Stress distribution in GaN nanopillars using confocal Raman mapping technique

“…Recently, Le Boulbar et al have studied the strain relaxation of etched and re-grown GaN nanorods using Raman spectroscopy. 19 They show that the GaN nanorods are fully relaxed in etched and re-grown structures. Re-growth of GaN onto the etched nanorods does not re-introduce strain in their studies.…”