Epitaxial ZnO films on (111) Si substrates with Sc₂O₃ buffer layers

Epitaxial (0001) ZnO films were grown on (111) Si substrates using epitaxial (111) Sc₂O₃ buffer layers. The quality of the ZnO epilayers is manifested by a Hall mobility of 77 cm²/V s at room temperature, x-ray diffraction rocking curve full widths at half maximum of 300–400 arc sec, and optical properties comparable to ZnO single crystals. Transmission electron microscopy studies reveal that a thin layer of SiO_x was formed at the Sc₂O₃/Si interface not during the Sc₂O₃ growth, but during the growth of the ZnO films. The thermal-mismatch induced residual strain in the films causes an energy shift of the exciton resonances in the photoluminescence spectrum. The redshifts are smaller than those of GaN films, indicating that the optical properties of ZnO are less strain sensitive.