Fabrication and optical properties of Mg_xZn_1-xO thin films

Mg_xZn_1 - xO (x \le 0.3) thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at room temperature. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The Mg content in the films is slightly larger than that in the targets. The refractive indices of Mg_xZn_1 - xO films measured at room temperature by spectroscopic ellipsometry (SE) on the wavelength 632.8 nm are systematically decreased with the increasing of Mg content. Optical band gaps of Mg_xZn_1 - xO films are determined by the transmittance spectra. With increasing Mg content, the absorption edges of Mg_xZn_1 - xO films shift to higher energies and band gaps linearly increase from 3.24 eV at x=0 to 3.90 eV at x =0.30.