HIGH-RESOLUTION X-RAY-DIFFRACTION STUDY OF ZNSE/GAAS HETEROSTRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY

We have used high-resolution X-ray diffraction (HRXRD) to study the strain relaxation in ZnSe/GaAs (001) heterostructures grown by molecular beam epitaxy (MBE). For layers thinner than a critical thickness, X-ray interference fringes are observed. Using a simulation program based on the dynamical theory, we are able to determine with high degree of precision the layer thickness and the (001) Poisson ratio of ZnSe. A transition from partially strained to fully relaxed layer is observed as a function of increasing film thickness for films thicker than a critical thickness, which is determined to be between 1600 to 1850 Angstrom. The (001) axis of the epilayer is observed to tilt away from the (001) axis of the substrate. The inclination angle for pseudomorphic layers is fairly constant. For films thicker than the critical thickness, there is no clear relationship between the tilt angle and the film thickness.