High Performance Transparent Conducting Films of Cadmium Indate Prepared by RF Sputtering

We are examining various spinel-structured thin films (e.g., Cd2SnO4, Zn2SnO4) to develop higher-quality transparent conducting oxides (TCO) than more conventional materials such as indium tin oxide. Here, we report on cadmium indate (CdIn2O4, CIO), which is another member of this family. Thin films of CIO were deposited by radio-frequency (RF) magnetron sputtering, from an oxide target, ontoborosilicate glass substrates. The variables included the substrate temperature, sputtering gas composition, and pressure. Film properties were measured before and after heat treatment. Characterization involved Hall effect measurements, optical and infrared spectrophotometry, X-ray diffraction, and atomic-force microscopy. Film resistivities as low as 2.3X10-4 .OMEGA. cm were achieved for afilm thickness of .55 .mu.m. The transmittance was 90% in the visible region of the spectrum, without correction for substrate losses and without an anti-reflection coating. The plasma resonance occurred at longer wavelengths than for other materials and this, with a bandgap of approximately 3.1 eV, presents a wide window for optical transmittance. The highest mobility was 54 cm2 V-1 s-1 and thehighest carrier concentration was 7.5X10 (sup 20) cm-3.