Ellipsometry Analysis of Mg<sub>x</sub>Zn<sub>1-x</sub>O Films on Silicon Substrates

Mg x Zn 1-x O films with hexagonal structure are prepared by radio frequency (rf) magnetron sputtering on Si substrate. The refractive indices and absorption coefficients of these films in the wavelength range from 300 to 800nm are determined by using ellipsometry at room temperature. The results show that the refractive index increases as the wavelength decreases in the transparent region (400-800nm). It reaches its maximum value around 340nm and 331nm, which is close to the fundamental absorption edge. Then the refractive index decreases as the wavelength gets shorter. The value of the refractive index is also a function of the Mg content. The higher the Mg content is in the film, the smaller the refractive index of the film is in the wavelength range from 330nm to 850nm. The band gap energy of the Mg x Zn 1-x O film is obtained by analyzing its absorption spectrum. An increase in the Mg content causes the fundamental absorption edge to shift toward shorter wavelength. In addition, UV and strong blue emission have been observed when the Mg x Zn 1-x O film is excited with light wave of 260nm at room temperature, and the emission mechanism is discussed.