Electrical and Optical Properties of Transparent Conducting Cadmium Stannate and Zinc Stannate Thin Films Prepared by RF Magnetron Sputtering

Cadmium stannate (Cd2SnO4) is a transparent conductive oxide (TCO) with potentially superior performance and lower cost than conventional meterials, such as indium tin oxide (ITO). However, due to concenrs about cadmium in some appl8ications, we have begun investigation of its non-toxic analog, zing stannate (Zn2SnO4). We report here elctrical and optical results for thin films of both cadmiumand zinc stannate. Films were prepared by radio frequency (RF) magnetron sputtering onto unheated or heated glass substrates. Some films were subsequently aneled at high temperature. Single-0phase polycrystalline spinel-type Cd2SnO4 films with sheet resistivities as low as 2 .OMEGA./.box. have been obtained for films 6500 .ANG. thick. These same Cd2SnO4 films showed .apprx.80% transmittanceacross the visible spectrum, with near-zero absorbance. These results compare favorably to commercially available TCOs, which typically show sheet resistances of about 10 .OMEGA./.box. for films that are about 80% transparent. The plama wavelength for Cd2SnO4 films occurred at about 1.mu.m. and reflectivity in the infrared (IR) reached about 90% by 5 .mu.m. Polycryatlline spinel-type Zn2SnO4films were found to have a relatively high optical bandgap (.apprx.3.9 eV) and showed .apprx.90% transmittanc3 across the visible spectrum. However, compared to Cd2SnO4 films, Zn2SnO4 films showed substantially inferior conductivity due to both lower carrier concentration and lower electron mobility. We have also investigated a perovskite phase zinc stannate, ZnSnO3, and report preliminaryresults for this material.