Effects of Substrate Radial-Position Relative to the Sputter-Gun Axis on the Electrical, Optical and Structural Properties of ZnO Thin Films Deposited by Reactive Direct Current Magnetron Sputtering

Abstract

ZnO thin films were deposited using reactive direct current (dc) magnetron sputtering on glasssubstrates placed at seven variable radial positions (-1, 0, 1, 2, 3, 4 and 5 cm) relative to thesputter-gun (target) axis. A pure zinc target was used and sputtering carried out in argon andoxygen atmosphere with flow rates of 50 sccm and 6 sccm, respectively. XRD characterizationshowed that, all films crystallized homogeneously in the wurtzite phase with a strong (002) and aweak (004) orientations. Film crystallinity was very low at substrate positions located less than orequal to 1 cm from the target axis but rapidly improved as substrate position increased beyond 1cm. Film thickness decreased steadily (from 320 to 160 nm) with increase in substrate positionfrom 1 to 5 cm. Film resistivity was much higher (over ~104 Ω cm) at substrate positions locatedless than 2 cm from the target axis and rapidly decreased with increase in substrate positionreaching the order ~10– 3 Ω cm at 3 cm and leveled out. Optical transmittance was homogeneouswith 86% in the wavelength range 380 – 2500 nm. Band gap increased dramatically (from 3.15 eVto 3.28 eV) with increase in substrate position.