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 glass substrates placed at seven variable radial positions (-1, 0, 1, 2, 3, 4 and 5 cm)  relative to the sputter-gun (target) axis. A pure zinc target was used and sputtering carried out in argon and oxygen atmosphere with flow rates of 50 sccm and 6 sccm, respectively. XRD characterization showed that, all films crystallized homogeneously in the wurtzite phase with a strong (002) and a weak (004) orientations. Film crystallinity was very low at substrate positions located less than or equal to 1 cm from the target axis but rapidly improved as substrate position increased beyond 1 cm. Film thickness decreased steadily (from 320 to 160 nm) with increase in substrate position from 1 to 5 cm. Film resistivity was much higher (over ~10⁴ Ω cm) at substrate positions located less than 2 cm from the target axis and rapidly decreased with increase in substrate position reaching the order ~10^{– 3} Ω cm at 3 cm and leveled out. Optical transmittance was homogeneous with 86% in the wavelength range 380 – 2500 nm. Band gap increased dramatically (from 3.15 eV to 3.28 eV) with increase in substrate position.

Keywords: Magnetron sputtering, substrate radial position, properties of ZnO thin films