STRUCTURAL CHARACTERIZATION AND INTERFACIAL STUDIES OF ZNSE BASED HETEROSTRUCTURES ON GAAS

Thin pseudomorphic ZnSe/CdxZn1-xSe/ZnSe quantum well structures and te rnary ZnSxSe1-x epilayers showing a nearly perfect crystalline structu re have been grown by molecular beam epitaxy (MBE). This has been demo nstrated by using high resolution X-ray diffraction and transmission e lectron microscopy (TEM). Concerning the X-ray diffraction, the struct ural information was obtained from rocking curves and their comparison to dynamical simulations as well as from reciprocal space maps. In th e 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 measu re of structural quality. This has been proved for a ZnSxSe1-x epilaye r which exhibits a gradient in sulphur concentration. Quantum well str uctures of sufficiently high structural quality offered the possibilit y 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 Ga As substrate and not caused by the MBE growth itself. For the best ZnS xSe1-x epilayers showing FWHM of the Bragg reflections equal to the th eoretical values (here 23 arc sec), the commonly used method of high r esolution X-ray diffraction reaches its limits in proving structural i mperfections.