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.