Evolution of the m-Plane Quantum Well Morphology and Composition within a GaN/InGaN Core–Shell Structure

Abstract

GaN/InGaN core−shell nanorods are promising for optoelectronic applications due to the absence of polarization-related electric fields on the sidewalls, a lower defect density, a larger emission volume, and strain relaxation at the free surfaces. The core−shell geometry allows the growth of thicker InGaN shell layers, which would improve the efficiency of light emitting diodes. However, the growth mode of such layers by metal organic vapor phase epitaxy is poorly understood. Through a combination of nanofabrication, epitaxial growth, and detailed characterization, this work reveals an evolution in the growth mode of InGaN epitaxial shells, from a two-dimensional (2D) growth mode to three-dimensional (3D) striated growth without additional line defect formation with increasing layer thickness. Measurements of the indium distribution show fluctuations along the <10−10> directions, with low and high indium composition associated with the 2D and 3D growth modes, respectively. Atomic steps at the GaN/InGaN core−shell interface were observed to occur with a similar frequency as quasi-periodic indium fluctuations along [0001] observed within the 2D layer, to provide evidence that the resulting local strain relief at the steps acts as the trigger for a change of growth mode by elastic relaxation. This study demonstrates that misfit dislocation generation during the growth of wider InGaN shell layers can be avoided by using pre-etched GaN nanorods. Significantly, this enables the growth of absorption-based devices and light-emitting diodes with emissive layers wide enough to mitigate efficiency droop.

Structural impact on the nanoscale optical properties of InGaN core-shell nanorods

“…Core-shell InGaN nanorods offer low defect density, non-polar sidewalls [10][11][12] on cheap foreign substrates. Thicker active regions may be grown 13 without leading to large spatial separations between the electrons and holes due to the mitigation of the QCSE. The combination of larger effective light emitting area and improved radiative efficiency provides scope for substantial reductions in the local carrier density, leading to a potential reduction in efficiency droop and ultimately higher efficiency light emitting devices.…”

Deep UV Emission from Highly Ordered AlGaN/AlN Core–Shell Nanorods

“…The defect band, initially observed in the AlN template, could be related to O-complexes and/or Si-complexes and other native defects, such as vacancies. ,,, The AlGaN SQW shows two emission energies: one centered around 5.13 eV (242 nm) on both the m -plane facets and semipolar facets and a second one centered around 5.22 eV (238 nm) having a higher intensity and localized at the corners between the semipolar and nonpolar nanorod facets. The small energy shift occurring at the corners between the semipolar and nonpolar planes could be due to a change of the surface morphology at the intersection, preferential incorporation of species as a result of strain relaxation at the corners, or from a local change of the QW thickness, similar to that observed for InGaN/GaN core–shell structures. , Note that the higher intensity could also result from a local change to the QW thickness or enhanced light extraction.…”

“…The small energy shift occurring at the corners between the semipolar and nonpolar planes could be due to a change of the surface morphology at the intersection, preferential incorporation of species as a result of strain relaxation at the corners, or from a local change of the QW thickness, similar to that observed for InGaN/GaN core− shell structures. 54,55 Note that the higher intensity could also result from a local change to the QW thickness or enhanced light extraction.…”

Growth mechanism of InGaN nanodots on three‐dimensional GaN structures

“…It means semi‐polar facets have the lowest diffusion barriers leading to Frank‐van der Merwe (layer‐by‐layer) growth among other facets. Recently, several works about Ehrlich−Schwöbel barriers (ESBs) were reported . ESBs inhibit the diffusion of adatoms and therefore, adatoms need to overcome ESBs to diffuse down to attach the lower step‐edge.…”