The scanning electron microscopy techniques of wavelength-dispersive X-ray (WDX) mapping, hyperspectral cathodoluminescence (CL), electron backscatter diffraction (EBSD) and electron channelling contrast imaging (ECCI) allow the investigation and correlation of the structural, compositional and luminescence properties of III-nitrides on the nanoscale.

WDX provides a quantitative measure of the composition of the material under study. CL provides information on a sample’s luminescence properties, where the luminescence spectrum is sensitive to strain, crystallinity, defects, doping and free carrier concentration. To directly correlate composition and luminescence properties, high-sensitivity WDX maps are acquired at the same time as CL spectra [1]. InN fluctuations in In_xGa_1-xN thin films have been measured on a scale of tens of nanometres [2].

To obtain a direct measure of the structural properties of III-nitrides we use the techniques of EBSD and ECCI [3]. An EBSD pattern is recorded by placing a phosphor screen in front of a highly tilted sample so that it intercepts electrons backscattered from the sample. An EBSD pattern provides a direct measurement of a sample’s crystal structure as it is a 2-D projection of the crystal structure. EBSD patterns acquired from a mesh of points on a sample can be used to produce maps of crystal structure, tilt, rotation and strain with a spatial resolution of order 20 nm.

ECCI exploits the fact that electrons will channel down the crystal planes of a suitably tilted sample. Images derived from these channelled electrons reveal defects which distort the crystal planes. Images with a resolution of tens of nanometres are obtainable.

We will report on recent results from In-containing III-nitrides produced by the RAINBOW Network [4].

1. R. W. Martin et al., phys. stat. sol. (a), 201 665 (2004).

2. P. R. Edwards et al., phys. stat. sol. (c), 0 2474 (2003).

3. C. Trager-Cowan et al., Phys. Rev. B 75, 085301 (2007).

4. http://rainbow.ensicaen.fr/

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1. Electron Channelling Contrast Imaging of Defects in Nitride Semiconductor Thin Films 
2. Sub-micron InGaN Ring Structures for High-efficiency LEDs