Spectroscopic ellipsometry and absorption study of Zn1-xMnxO/Al2O3 (0<=x<=0.08) thin films.

We grow Zn1-xMnxO/Al2O3 (0<=x<=0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5 eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B 56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3 eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3 eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization. [ABSTRACT FROM AUTHOR]