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 H 2 O 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 × 10 −4 to 4.5 × 10 −4 Ω-cm, the carrier concentration increases from 9.7 × 10 20 to 1.2 × 10 21 cm −3 , the specific contact resistance decreases from 4.4 × 10 −4 to 7.5 × 10 −5 Ω-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.