Reciprocal Space Mapping of MBE-Grown HgCdTe Heterostructures

Lattice mismatch between substrates and epitaxial layers of different mole-fractions can create a variety of distortions and defects in HgCdTe epilayers, thus degrading the performance of infrared detectors fabricated from this material. X-ray diffractometry is a sensitive non-destructive technique, which allows in-depth characterisation of the crystal lattice prior to detector fabrication. We present results of triple-axis diffractometry (TAD) performed on single and double layer HgCdTe films grown on (211)B CdZnTe substrates by molecular beam epitaxy (MBE). The positions of both surface-symmetric and asymmetric diffraction peaks have been used to extract lattice spacings parallel and perpendicular to the (211) growth direction. The unstrained lattice parameter of each epilayer has been calculated assuming that the layers are elastically strained. The low-symmetry of the (211) plane, coupled with the anisotropic elasticity of zinc-blende semiconductors, results in monoclinic distortion of the lattice, as observed in these samples. In double layer samples, the mosaicity of both layers is greater than that observed in single epilayers. Annealed samples show greater lattice distortion than as-grown samples