Optical characterization by variable angle spectroscopic ellipsometry of nitrogen-doped MgxZn1 − xO thin films prepared by the plasma-assisted reactive evaporation method

Abstract

Non-doped MgxZn1−xO films (MgxZn1−xO films) and nitrogen-doped MgxZn1−xO films (MgxZn1−xO:N films) were grown epitaxially on Zn faces of ZnO single crystal substrates by the plasma-assisted reactive evaporation (PARE) method using ZnMg alloys. Optical parameters, refractive index n, extinction coefficient k, and absorption coefficient α of these films and ZnO substrate were easily estimated by variable angle spectroscopic ellipsometry. The k values of these films abruptly increased with increase in photon energy near the absorption edge region. Dispersions of n of these films were sharper with larger peak values than that of a ZnO substrate. MgxZn1−xO films and MgxZn1−xO:N films grown on a ZnO substrate by the PARE method are of high quality with less defects than those of a ZnO substrate. Maximum value of α of these films calculated from k was about 2×105cm−1. The values of intercepts on photon energy hν axis of (αhν)2‐hν plots for these films and the ZnO substrate agree with peak energy of PL spectra, the origin of which is free excitons. These results indicate that absorption in those materials is dominated by exciton absorption.