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

Research output: Contribution to journalArticle

Abstract

Nanofocus x-ray diffraction is used to investigate the structure and local strain field of an isolated (In,Ga)N/GaN core-shell microrod. Because the high spatial resolution of the x-ray beam is only 80×90 nm2, 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 high-angle 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 finite-element 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.

Details

Authors
  • Thilo Krause
  • Michael Hanke
  • Lars Nicolai
  • Zongzhe Cheng
  • Michael Niehle
  • Achim Trampert
  • Maik Kahnt
  • Gerald Falkenberg
  • Christian G. Schroer
  • Jana Hartmann
  • Hao Zhou
  • Hergo Heinrich Wehmann
  • Andreas Waag
External organisations
  • Paul-Drude-Institut für Festkörperelektronik
  • German Electron Synchrotron (DESY)
  • University of Hamburg
  • Technical University of Braunschweig
Original languageEnglish
Article number024033
JournalPhysical Review Applied
Volume7
Issue number2
Publication statusPublished - 2017 Feb 28
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes