High-Resolution X-Ray Diffraction Studies of Molecular Beam Epitaxy-Grown HgCdTe Heterostructures and CdZnTe Substrates

Lattice mismatch between substrates and epitaxial layers of different mole-fractions can create a variety of distortions and defects in Hg(1-x)Cd(x)Te epilayers, thus degrading the performance of infrared detectors fabricated from this material. X-ray diffraction is a sensitive nondestructive technique, which allows in-depth characterization of the crystal lattice prior to detector fabrication. We present results of triple-axis diffractometry performed on single- and double-layer HgCdTe films grown on (211)B CdZnTe substrates by molecular beam epitaxy (MBE). In this study, both the omega and 2 theta diffraction angles have been recorded absolutely so that the diffraction peaks in the RSMs can be positioned directly in reciprocal space, without requiring reference to a substrate peak. 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 relaxed lattice parameter of each epilayer has been calculated assuming that the layers are elastically strained. The low symmetry of the (211) growth direction, 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. Layers subjected to a Hg-saturated anneal show greater lattice distortion than as-grown samples.