Effects of Oxygen Plasma Post-Treatment on Ga-Doped ZnO Films Grown by Thermal-Mode ALD

Gallium-doped zinc oxide (GZO) thin films were grown via thermal-mode atomic layer deposition (TM-ALD) at different deposition temperatures. Diethylzinc (DEZ), triethylgallium (TEG), and H2O were used as zinc, gallium precursors, and oxygen source, respectively. ALD-GZO thin films are constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. In order to eliminate the residual hydroxyl groups, we have employed the oxygen ion bombardment on ALD-GZO film surface. The influences of O-2 plasma post-treatment on the surface morphology, surface chemical property, electrical, and optical characteristics of GZO films are investigated. With enhancing the O-2 plasma power, the performance of GZO films would be improved. As a result of exposure to 200-W plasma power, the resistivity decreases from 6.7 x 10(-4) to 4.5 x 10(-4) Omega-cm, the carrier concentration increases from 9.7 x 10(20) to 1.2 x 10(21) cm(-3), the specific contact resistance decreases from 4.4 x 10(-4) to 7.5 x 10(-5) Omega-cm(2) for Ti/Al contact, the surface property changes from hydrophilic to hydrophobic behavior, the bandgap energy varies from 3.7 to 3.8 eV for Burstein-Moss shift phenomenon, and the mean optical transmittance keeps above 90% in the visible spectrum. On the other hand, the transmittance decreases with O-2 plasma power in the near- and mid-infrared regions. (C) 2013 The Electrochemical Society. All rights reserved.