Thesis

Electron channelling contrast imaging of nitride semiconductor thin films

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13328
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Abstract
  • This work reports on the development of a scanning electron microscopy based technique known as electron channelling contrast imaging for characterising extended defects in nitride semiconductors. Extended defects in nitride semiconductors act as scattering centres for light and charge carriers and thus limit the performance of optoelectronic devices. Developing the capability to rapidly analyse extended defects, namely threading dislocation and stacking fault densities without any sample preparation represents a real step forward in the development of more efficient nitride-based semiconductor devices. In electron channelling contrast imaging, changes in crystallographic orientation, or changes in lattice constant due to local strain, are revealed by changes in grey scale in an image constructed by monitoring the intensity of backscattered electrons as an electron beam is scanned over a suitably oriented sample. Extremely small orientation changes are detectable, enabling small angle tilt and rotation boundaries and extended defects to be imaged. Images with a resolution of tens of nanometres are obtainable with electron channelling contrast imaging. Vertical threading dislocations are revealed as spots with black-white contrast in electron channelling contrast imaging. A simple geometric procedure was developed which exploits the differences observed in the direction of this black-white contrast for screw, edge, and mixed dislocations for two electron channelling contrast images acquired from two symmetrically equivalent crystal planes. By using this procedure, an order of magnitude reduction in the time required to obtain quantitative information on dislocations is envisaged compared to the presently available techniques. The use of electron channelling contrast imaging to reveal and characterise basal plane stacking faults and partial dislocations in m-InGaN thin films and quantifying threading dislocations in InAlN thin films is also demonstrated. Preliminary work on combining electron channelling contrast imaging and cathodoluminescence imaging has been demonstrated for the first time to understand the effect of threading dislocations on light emission characteristics in nitride semiconductors.
Resource Type
DOI
Date Created
  • 2012
Former identifier
  • 967036

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