Elucidating surface properties of dry-etched ZnO using H2/CH4 and H2/CH4/Ar plasma

This paper reports a study of reactive ion etching (RIE) of n-ZnO in H2/CH4 and H2/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 H2 gas without mixed CH4 gas. The highest etching rate was obtained from physical etching of H2/Ar species associated with chemical reaction of CH4 species. Additionally, the H2/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).