High-performance, transparent conducting oxides based on cadmium stannate

We discuss the modeling of thin films of transparent conducting oxides and we compare the predictions with the observed properties of cadmium stannate. Thin films of this material were deposited using radio-frequency magnetron sputtering. The Drude free-carrier model is used to model the optical and electrical properties. The model demonstrates the need for high mobilities. The free-carrier absorbance in the visible spectrum is used as a comparative figure-of-merit for cadmium stannate and tin oxide. This shows that free-carrier absorbance is much less in cadmium stannate than in tin oxide. X-ray diffraction shows that annealed films consist of a single-phase spinel structure. The postdeposition annealing sequence is shown to be crucial to forming a single phase, which is vital for optimal optical and electrical properties. The films are typically high mobility (up to 65 cm(2) V-1 s(-1)) and have carrier concentrations as high as 10(21) cm(-3). Resistivities are as low as 1.3 10(-4) Omega cm, the lowest values reported for cadmium stannate. Atomic force microscopy indicates that the root-mean-square surface roughness is approximately +/- 15 Angstrom. Cadmium stannate etches readily in both hydrofluoric and hydrochloric acid, which is a commanding advantage over tin oxide.