STRUCTURAL CHARACTERIZATION AND INTERFACIAL STUDIES OF ZNSE BASED HETEROSTRUCTURES ON GAAS

Thin pseudomorphic ZnSe/CdxZn1-xSe/ZnSe quantum well structures and ternary ZnSxSe1-x epilayers showing a nearly perfect crystalline structure have been grown by molecular beam epitaxy (MBE). This has been demonstrated by using high resolution X-ray diffraction and transmission electron microscopy (TEM). Concerning the X-ray diffraction, the structural information was obtained from rocking curves and their comparison to dynamical simulations as well as from reciprocal space maps. In the case of nearly perfect layers a simple estimation of the full width at half maximum (FWHM) of the rocking curve cannot be taken as a measure of structural quality. This has been proved for a ZnSxSe1-x epilayer which exhibits a gradient in sulphur concentration. Quantum well structures of sufficiently high structural quality offered the possibility of testing the existence of intermediate compound layers at the III-V/II-VI interface and of composition gradients at the well interfaces. The interface sharpness found is restricted by the waviness of the GaAs substrate and not caused by the MBE growth itself. For the best ZnSxSe1-x epilayers showing FWHM of the Bragg reflections equal to the theoretical values (here 23 arc sec), the commonly used method of high resolution X-ray diffraction reaches its limits in proving structural imperfections.