Mesoscopic and Condensed Matter Physics

Biography

Biography: Sadık Guner

Abstract

The pure ZnO and Cr doped ZnO (Cr:ZnO) thin films (thickness: 200 nm) were grown on both side polished silica (SiO₂) substrates by RF magnetron sputtering at room temperature. As deposited samples were annealed at 400 °C, 500°C and 600 °C for 45 min in quartz annealing furnace system, respectively. The structural and chemical composition analyses were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectrometry (EDS). XRD studies revealed that the almost single crystalline hexagonal Wurtzite structure of pure ZnO film disappears with increasing Cr concentration and annealing process contributes the long range crystal order of films. SEM images show that average grain size is around 30 nm. EDS results indicate that only Zn, Cr and O elements are present in the Cr:ZnO thin films. The electrical properties were investigated by using the Four Point Probe (FPP) method. The smallest electrical resistivity for doped samples were obtained at 600 °C  annealing temperature and specifically as 5.34×10⁻⁴ Ω⋅cm belonging to Cr_8.21ZnO. The electrical conductivity and carrier concentration of the films are increased while mobility carriers are decreased with increasing Cr content. The optical properties were studied in the wavelength region of 200-1000 nm by employing UV-vis spectroscopy. Pure ZnO and Cr:ZnO films that include 3.22 at. % Cr content (or less), have transmittance above 70 % between 400-1000 nm before annealing.  It was observed that all annealed samples have higher average transmittance in the range of 200–1000 nm as compared to as-deposited films. Tauc plots were drawn to specify the optical energy band gap (E_g) of  as-deposited and annealed samples. The E_g increases from 3.24 eV to 3.90 eV with incrasing Cr concent from x: 0 at. % to 3.22 at. % and then decreases to 1.60 eV for 11.80 % Cr concentration.