High resolution X-ray diffraction studies of CdxHg1- xTe/ CdTe epitaxial layers grown by MOVPE on GaAs substrates

Abstract

We have applied high resolution X-ray diffractometry and topography techniques to investigate both the lateral uniformity and structural properties of Cd x Hg 1− x Te layers grown by MOVPE onto CdTe buffer layers on GaAs. On samples ∼1–2 cm square, maps of rocking curve width (β) have shown values varying from 60 arc sec (comparable to the best reported) to over 1000 arc sec on the same slice, indicating the superior value of mapping over single point measurements on this material. A good correlation has been observed between rocking curve widths, lattice tilts and the density of pyramid-like surface defects, the last of which are also associated with an increased twin density. However, on rotating the sample about its surface normal, the 400 surface symmetric β-value varies by up to an order of magnitude, indicating that lattice tilts play an important role in broadening the rocking curve. X-ray topography reveals large tilt boundaries in the CMT epilayer which correlate with the dislocation structure in the GaAs substrate.