Strain Determination in Quasi-Lattice-Matched LWIR HgCdTe/CdZnTe Layers

We take advantage of the zinc distribution of (211)B CdZnTe substrates to probe the lattice-mismatch-induced stress in long-wave infrared HgCdTe layers grown by molecular beam epitaxy. High-resolution x-ray diffraction is used to accurately determine the strain-free lattice parameters of both CdZnTe and HgCdTe, together with the in-plane components of the stress tensor. By using several wafers, the stress evolution is derived over a broad range of lattice mismatch. In particular, stress relaxation is evidenced for mismatch greater than 0.02% and 0.04% for tensile and compressively strained HgCdTe, respectively. In-plane strain anisotropy, expected for the (211) orientation, is only evidenced for the compressive configuration. Strain relaxation is correlated with substrate curvature and rocking-curve peak broadening, providing indirect evidence for plastic relaxation.