This paper reports a study of reactive ion etching (RIE) of n-ZnO in H-2/CH4 and H-2/CH4/Ar gas mixtures. Variables in the experiment were gas flow ratios, radio-frequency (rf) plasma power, and total pressure. Structural and electrical parameters of the etched surfaces and films were determined. Both the highest surface roughness and highest etching rate of ZnO films were obtained with a maximum rf power of 300 W, but at different gas flow ratios and working pressures. These results were expected because increasing the rf power increased the bond-breaking efficiency of ZnO. The highest degree of surface roughness was a result of pure physical etching by H-2 gas without mixed CH4 gas. The highest etching rate was obtained from physical etching of H-2/Ar species associated with chemical reaction of CH4 species. Additionally, the H-2/CH4/Ar plasma treatment drastically decreased the specific contact and sheet resistance of the ZnO films. These results indicated that etching the ZnO film had roughened the surface and reduced its resistivity to ohmic contact, supporting the application of a roughened transparent contact layer (TCL) in light-emitting diodes (LEDs). (C) 2010 Elsevier B. V. All rights reserved.