Thermally induced strain in ZnSe and GaN epitaxial layers studied by high-resolution X-ray diffraction at variable temperatures

High-resolution X-ray diffraction at variable temperatures was used to stud y the strain slate in ZnSe layers of different thicknesses grown on GaAs(00 1) substrates and of GaN layers deposited on sapphire. In the ZnSe layers, a biaxial compressive strain component due to the lattice mismatch and a bi axial tensile strain due to the different thermal expansion coefficients ar e superposed which in general can be well modelled. However, the assumption s of the model may be violated for partially relaxed layers. A residual lat tice misfit induced strain is present in ZnSe layers as thick as 5.4 mu m O n the contrary, the strain state in GaN layers is given by a superposition of biaxial thermally induced strain and hydrostatic strain, presumably indu ced by impurity incorporation.