Spectroscopic Ellipsometric Study of ZnO and Zn1−xMgxO Thin Films Grown on (0001) Sapphire Substrate

We grew ZnO and Zn1−xMgxO thin films on (0001) sapphire substrates by using metal-organic vapor phase epitaxy and measured the pseudo-dielectric functions using variable-angle spectroscopic ellipsometry. We analyzed the pseudo-dielectric functions by using the multi-layer model. The dielectric functions were fitted by using a Holden model dielectric function. We used anisotropic layer modeling for the ZnO thin film, whereas we adopted the approximation of isotropic layer modeling for the Zn1−xMgxO alloys. We also discuss the Mg composition dependence of the band-gap and the binding energy in Zn1−xMgxO alloys, and consider the valence-band ordering in ZnO thin films