Lattice distortion of thick epitaxial layers

Precise x-ray diffraction measurements between room temperature and similar to 400 degrees C (Bond method) exhibit some details in the variations of strain in similar to 1 mu m thick epitaxial layers of GaAs, InP, CdTe, EuS, or SrS on Si or GaAs substrates. The lattice parameters of the cubic layers, which are deposited at high temperatures, deviate from the lattice parameters, a(0), of small unconstrained single crystals by Delta a/a(0) = epsilon(0) less than or similar to 10(-3). The layers adhere to the substrates below T-c and adopt different strains, epsilon(parallel to) and epsilon(perpendicular to), parallel and perpendicular to the substrate. Frequently the T-c and epsilon(0) values vary on annealing at 160-400 degrees C. The ratio E = - (epsilon(perpendicular to) - epsilon(0))/(epsilon(parallel to) - epsilon(0)) remains constant for each sample. The change of the relative volume Delta V/V-0 = epsilon(parallel to) (2 - E) + epsilon(0) (1 + E) at the variation of epsilon(parallel to) and epsilon(0) can give rise to corrugations, blisters, or microcracks in the epitaxial layers. Stable epitaxial layers with constant epsilon(0) and T-c values can be obtained by deposition on buffer layers or stepped substrates.