Fabrication and evaluation of a Si/ZnO/HfO2 buried heterostructure through internal oxidation

Metal-oxides are in the forefront of various applications in optoelectronic, piezo-electronics, magnetism etc. The large bandgap oxide semiconductor hetero-interface growth can be achieved through a controlled conversion of the metallic part of a group II elements of the compound. This study investigates the controlled in-vitro growth of zinc oxide (ZnO) thin films on n-type silicon substrates through the internal oxidation of a buried metallic Zn layer under hafnium dioxide (HfO₂). Controlled annealing in an oxygen atmosphere at 400 °C resulted in the transformation of the underline Zn layer of thickness 44 nm into ZnO layer of thickness 37.5 nm. The comparative structural analysis of the as-grown and annealed Zn/HfO₂ layers by x-ray diffraction clearly indicates complete conversion of the Zn layer to ZnO/HfO_x hetero-interface, where x < 2. The x-ray reflectivity and x-ray photoelectron spectroscopy clearly indicates non-stoichiometry in the HfO₂ layer indicating diffusion of O to the underlying Zn layer to convert it to ZnO. The presence of well-defined fringes in the x-ray reflectivity clearly suggest high quality hetero-interfaces which allows us to determine the interfacial layer thicknesses. Low temperature photoluminescence spectra taken at 4 K clearly showed sharp and well-defined multiple order near band edge emission peaks at around 3.37 eV, which falls in the UV region of the spectra. The findings underscore the potential of this method for developing oxide-based buried low-dimensional heterostructures for different applications.