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Keywords:

  • Scanning transmission electron microscopy (STEM);
  • High-resolution;
  • Z-contrast;
  • ADF;
  • HAADF;
  • Electron energy loss spectroscopy (EELS);
  • ZnSxSe1 − x/ZnSe quantum wells;
  • MOVPE

Abstract

Epitaxial growth techniques for ZnSxSe1 − x/ZnSe heterostructures have already achieved a high degree of development. Further improvements strongly require characterisation techniques with high compositional sensitivity and high spatial resolution. Therefore in this work high-resolution Z-contrast, which provides compositional information down to the atomic scale, has been used for the first time to characterise ZnSxSe1 − x/ZnSe quantum well structures. The influence of structural defects on Z-contrast is demonstrated by comparison of scanning transmission electron microscopy (STEM) bright field images and STEM Z-contrast micrographs of planar defects and dislocations. The compositional abruptness of ZnSxSe1 − x/ZnSe interfaces in MOVPE-grown quantum well (QW) structures is judged from high-resolution Z-contrast micrographs. Electron energy loss spectroscopy (EELS) measurements were performed for the first time in ZnSxSe1 − x/ZnSe QW structures in order to obtain quantitative compositional information with nanometre spatial resolution. From EELS line scans, which monitor the selenium concentration across ZnSe QWs, the obtainable spatial resolution is estimated to be about 1–2 nm. The problems that have prevented quantitative analysis of the selenium concentration up to now are discussed.