Structure and Composition of Isolated Core-Shell(In,Ga)N/GaNRods Based on Nanofocus X-Ray Diffraction and Scanning Transmission Electron Microscopy

Abstract

Nanofocus x-ray diffraction is used to investigate the structure and local strain field of an isolated ðIn; GaÞN=GaN core-shell microrod. Because the high spatial resolution of the x-ray beam is only 80 × 90 nm 2 , we are able to investigate several distinct volumes on one individual side facet. Here, we find a drastic increase in thickness of the outer GaN shell along the rod height. Additionally, we performed highangle annular dark-field scanning-transmission-electron-microscopy measurements on several rods from the same sample showing that (In,Ga)N double-quantum-well and GaN barrier thicknesses also increase strongly along the height. Moreover, plastic relaxation is observed in the top part of the rod. Based on the experimentally obtained structural parameters, we simulate the strain-induced deformation using the finiteelement method, which serves as the input for subsequent kinematic scattering simulations. The simulations reveal a significant increase of elastic in-plane relaxation along the rod height. However, at a certain height, the occurrence of plastic relaxation yields a decrease of the elastic strain. Because of the experimentally obtained structural input for the finite-element simulations, we can exclude unknown structural influences on the strain distribution, and we are able to translate the elastic relaxation into an indium concentration which increases by a factor of 4 from the bottom to the height where plastic relaxation occurs.

Direct imaging of Indium-rich triangular nanoprisms self-organized formed at the edges of InGaN/GaN core-shell nanorods

“…Even within these domains different indium concentrations are observed, as shown in the nanoprisms. Issues like the different indium incorporation on different crystal facets 32 – 39 , the sophisticated strain distribution for three dimensional grown structures 40 – 45 as well as surface conditions 25 and atomic configurations 39 , 46 could have a significant influence on the indium incorporation in InGaN nanorod shell layers. We want to point out that the growth mechanism of these domains is much more complex compared to the proposed model of Griffiths et al .…”

Electron Tomography of Pencil-Shaped GaN/(In,Ga)N Core-Shell Nanowires

“…2a). This selected probe volume must be filled with carbon to protect the NW during the FIB milling process [21]. Carbon depositions were carried out in two steps in order to reduce the Ga contamination: (i) firstly, by electron beam-induced carbon deposition to fill the volume between the NWs (Fig.…”

Role of Underlayer for Efficient Core–Shell InGaN QWs Grown on m-plane GaN Wire Sidewalls

“…Figure 5areveals a significant number of bright lines corresponding to extended defects originating from the first QW when the QWs are directly grown on wire sidewalls, whereas no defect is visible in the case of GaN spacer growth (Figure 5c). TheFigure S6in the supporting information shows a STEM image of selected zone with and w/o GaN spacer that clearly confirms the absence of extended defects in presence of the GaN spacer.InGaN/GaN core-shell wires usually exhibit stacking faults (SFs) showing contrast perpendicular to the QWs.4,48 Detailed investigation of the SFs in the case of planar QWs on m-plane GaN systems reveals that these defects plastically relax the misfit strain accumulated during the growth process along the !̅ -direction 49,50. The pronounced difference between the defect densities in the two images is clearly related to the growth of the GaN spacer.…”