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

Abstract

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 O2 plasma post-treatment on the surface morphology, surface chemical property, electrical, and optical characteristics of GZO films are investigated. With enhancing the O2 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 × 10−4 to 4.5 × 10−4 Ω-cm, the carrier concentration increases from 9.7 × 1020 to 1.2 × 1021 cm−3, the specific contact resistance decreases from 4.4 × 10−4 to 7.5 × 10−5 Ω-cm2 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 O2 plasma power in the near- and mid-infrared regions.