CaF2 growth as a buffer layer of ZnO/Si heteroepitaxy

This report describes an improvement of the CaF2 buffer layer for the heteroepitaxy of the ZnO films on Si (1 1 1) substrates. In the heteroepitaxy, the quality of CaF2 buffer layer plays an important role to transmit the epitaxial relationship from Si to ZnO by suppressing the oxidation of substrate surface. Although CaF2 has a closely matched lattice constant to Si, a low-temperature (LT) growth by two-step procedure is found to be important to grow uniform CaF2 layers free from rotational domains, and the structural and optical properties of the ZnO films on Si are dramatically improved by the use of LT grown CaF2 as the buffer layer.