Nondestructive analysis of structural defects in wide bandgap II-VI heterostructures

Abstract

X-ray scattering measurements of wide bandgap II-VI heterostructures show that stacking faults (which nucleate defects that are responsible for optical degradation of light emitting diodes and lasers) introduce significant levels of diffuse scattering near Bragg reflections of both the epitaxial layers and the GaAs substrate. We employed triple axis x-ray diffraction techniques to investigate stacking fault diffuse scattering and used cathodoluminescence and transmission electron microscopy to independently measure the stacking fault density. For comparison, double axis scans from the same samples were largely incapable of detecting the presence of these defects. Measurements taken at different azimuthal positions exhibit different levels of diffuse scattering and the diffuse scattering intensity is related to the stacking fault intensity in each <110> direction, which suggests that this technique can provide a non-destructive assessment of defects present in these systems. For some samples, the ZnSe buffer layer exhibited a tilt with respect to the substrate along a <110> direction; this tilt was greater than the tilt which would be attributed to growing a strained layer on the slightly miscut substrates which were used here.