Achieving high-efficiency photoanodic behavior with a low-mobility oxide, In/sub 2/O/sub 3/

The authors report the solid-state and photoelectrochemical properties of thermally grown and reactively sputtered In/sub 2/O/sub 2/ films of mean thickness <2000A grown on bare Pyrex, platinum, gold, and ITO. The colloidally rough, thermally grown films on bare Pyrex flats exhibited quantum efficiencies near unity at 310 nm, while the same thickness of uniformly flat In/sub 2/O/sub 3/ reactively sputtered directly onto Pyrex displayed no detectable photoresponse. Comparison of the morphological, solid-state, optical, and photoelectrochemical properties indicate that there are two sources contributing to the superior behavior of the collidally rough films over the uniform flat films. The first is an improvement in the solid-state properties of the thermally grown films which gives rise to both a substantial increase in the majority carrier mobility and a much wider space charge region due to a reduced doping density. The second is purely geometrical in nature with the rough morphology leading to more minority carriers being generated near the semiconductor-electrolyte interface (roughness-enhanced transport) as well as to more light being absorbed in the rough films than in smooth films of the same mean thickness (roughness-enhanced absorption)