Tailoring the optical properties of Mg x Zn1−x O thin films by nitrogen doping

Abstract

Thin films of MgxZn1−xO and MgxZn1−xO doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm2 and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped MgxZn1−xO thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for MgxZn1−xO thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.