Optical and electrical properties of gallium doped indium tin oxide optimized for low deposition temperature applications

In optoelectronic and photovoltaic devices, transparent conductive oxides are important in establishing a good electrical contact while minimizing optical losses over a broad range of wavelengths (400-1200 nm). To date, research has focused on In2O3 - SnO2 (ITO) films. In this paper, we report on a study of Ga-doped ITO (GITO) films, which in contrast to standard ITO 90/10 (i.e. In:Sn = 90:10) films contain less In. Initially, we describe the development of a multicomponent Ga-In-Sn oxide target with a Ga:In:Sn ratio of 4:64:32, which was used in a radio-frequency sputtering system to deposit GITO thin films on glass substrates. Furthermore, we describe the microstructural/structural (scanning electron microscopy and X-ray diffraction spectroscopy), optical (wavelength dependent complex refractive indices) and electrical (resistivity, mobility, free carrier density) measurements used to optimize sputtering conditions and post-annealing processing. As well as achieving an optimized/improved GITO thin film deposited at high substrate and annealing temperatures, we obtained promising thin GITO films with excellent optical properties and with relatively low resistivity (1.7 mΩcm) deposited and annealed at temperatures around 200 °C.