Nanoscopic Insights into InGaN/GaN Core–Shell Nanorods: Structure, Composition, and Luminescence

Abstract

Nitride-based three-dimensional core-shell nanorods (NRs) are promising candidates for the achievement of highly efficient optoelectronic devices. For a detailed understanding of the complex core-shell layer structure of InGaN/GaN NRs, a systematic determination and correlation of the structural, compositional, and optical properties on a nanometer-scale is essential. In particular, the combination of low-temperature cathodoluminescence (CL) spectroscopy directly performed in a scanning transmission electron microscope (STEM), and quantitative high-angle annular dark field imaging enables a comprehensive study of the nanoscopic attributes of the individual shell layers. The investigated InGaN/GaN core-shell NRs, which were grown by metal-organic vapor-phase epitaxy using selective-area growth exhibit an exceptionally low density of extended defects. Using highly spatially resolved CL mapping of single NRs performed in cross-section, we give a direct insight into the optical properties of the individual core-shell layers. Most interesting, we observe a red shift of the InGaN single quantum well from 410 to 471 nm along the nonpolar side wall. Quantitative STEM analysis of the active region reveals an increasing thickness of the single quantum well (SQW) from 6 to 13 nm, accompanied by a slight increase of the indium concentration along the nonpolar side wall from 11% to 13%. Both effects, the increased quantum-well thickness and the higher indium incorporation, are responsible for the observed energetic shift of the InGaN SQW luminescence. Furthermore, compositional mappings of the InGaN quantum well reveal the formation of locally indium rich regions with several nanometers in size, leading to potential fluctuations in the InGaN SQW energy landscape. This is directly evidenced by nanometer-scale resolved CL mappings that show strong localization effects of the excitonic SQW emission.

Photon bunching reveals single-electron cathodoluminescence excitation efficiency in InGaN quantum wells

“…In CL, a high-energy electron beam in a scanning electron microscope (SEM) excites a material and generates luminescence that is collected and analyzed. CL emission gives valuable spatially resolved information about the band gap [7,8], carrier generation [9], defects [10,11], diffusion and carrier transport [12][13][14], recombination [15,16], and other optoelectronic properties of semiconductors that are used, e.g., in light-emitting diodes (LEDs) [17,18], lasers [19], solar cells [20], and more.…”

Wafer-scale Thermodynamically Stable GaN Nanorods via Two-Step Self-Limiting Epitaxy for Optoelectronic Applications

“…This further enhances the LED characteristics by removing the phosphor conversion efficiency, as well as improving device reliability which may be caused by phosphor degradation due to prolonged exposure to internally generated heat. Such nanorod and phosphorless LED devices are actively being developed at both academic and industry labs due to its possibility of out-performing its planar counterpart8262728. The shell layer consists of 10-pairs of InGaN/GaN super-lattice for strain relief, 3-paris of InGaN/GaN multi-quantum well and barrier layers, AlGaN electron blocking layer to prevent electron overflow at high current densities, and a p-GaN layer for hole carrier injection.…”

“…It is also possible to monolithically integrate GaN devices with silicon technology to further enhance the functionality of conventional CMOS devices7. Both catalyst-assisted and catalyst-free growth of III-V nanorods have been demonstrated and studied in various epitaxial growth systems in terms of growth morphology and uniformity68910. Growth of nanostructures practically eliminates extended defect formations (e.g.…”

Thermodynamic photoinduced disorder in AlGaN nanowires

“…the characteristic charge carrier mobility and lifetime) reflect the nature and quality of semiconductor device materials, 46 and is influenced by device architecture, the nature and dimensions of the materials and interfaces involved, and operational mode. 47 Examples include semiconducting zero-dimensional (0D) nanocrystals (NCs) and quantum dots (QDs), 48,49 1D nanowire solar cells, 50 two-dimensional (2D) GaN, 51 and three-dimensional (3D) InGaN/GaN core-shell nanorods 52 and nanoscale silicon-based transistors, 53,54 which can demonstrate opto-electrical, photovoltaic, and signal switching properties superior to those of their bulk and large-area counterparts.…”