Formation mechanism of Zn2SiO4crystal and amorphous SiO2in ZnO/Si system

In our recent study Xu et al (2002 Chem. Phys. Lett. 364 57–63), a phase transformation from the hexagonal to the tetragonal structure in the annealed ZnO films on silicon was studied by atomic force microscopy. Cathodoluminescence (CL) and glancing-angle x-ray diffraction analysis of the ZnO films indicated that such a transformation is due to the generation of a tetragonal zinc silicate. In order to identify the formation mechanism of the zinc silicate and the bottom broadening of the UV band, a depth profile secondary ion mass spectroscopy experiment was carried out. The results show that vast atomic diffusion between the ZnO film and the silicon substrate occurred due to the annealing temperature. Such interdiffusion can create not only a mixed crystal of ZnO and Zn2SiO4, but also an amorphous silicon dioxide (a-SiO2) in a deep range from the surface to the interface of the ZnO/Si system. The a-SiO2 is most probably the source of the 453 nm blue band hidden in the tail of the 390 nm UV band, since the blue band agrees with the CL spectra of the amorphous quartz glass and the thermally oxidized silicon.