Structural properties of Cu_2O epitaxial films grown on c-axis single crystal ZnO by magnetron sputtering

摘要

Epitaxial Cu_2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu_2O films exhibit a columnar growth manner apart from a ～5 nm thick CuO interfacial layer. In comparison to the reactively sputtered Cu_2O, the ceramic-sputtered films are less strained and appear to contain nanovoids. Irrespective of polarity, the Cu_2O grown by reactive sputtering is observed to have (111)Cu_2O||(0001)ZnO epitaxial relationship, but in the case of ceramic sputtering the films are found to show additional (110)Cu_2O reflections when grown on O-polar surface. The observed CuO interfacial layer can be detrimental for the performance of Cu_2O/ ZnO heterojunction solar cells reported in the literature.