Ga doped ITO transparent conductive oxide: Optical and electrical properties at different deposition conditions

Abstract

In the optoelectronics, especially in thin-film photovoltaics, the transparent conductive oxides (TCO) play an important role to minimize the front contact optical losses. The TCOs used as a front contact needs to have low resistivity (<1 mOhmcm), high optical transparency in the broad wavelength region (>80% at 400-1000 nm) and high temperature stability. In the case of using nano-imprinted lithography for reproduction of the morphologies the good electrical and optical properties should be obtained at low deposition or post-annealed temperatures. To translate the morphology, at which the light is efficiently scattered, to the internal interfaces of the solar cells very low thickness of TCO is required (<200 nm). One of such candidates is Ga doped SnO2:In (ITO), which exhibits better optical and similar electrical properties to ITO 90/10, additionally it has lower indium content. A multicomponent Ga-In-Sn oxide target with Ga:In:Sn = 4:64:32 metal ratio was prepared, that was used in RF sputtering system for deposition of high quality GITO thin-film layers on glass. In this study, we will focus on electrical (specific resistivity, mobility and carrier concentration) and optical properties (thickness and refractive index) as a function of deposition and annealing parameters. The results of optical and electrical characterization of the two best GITOs will be presented, one globally optimized and one optimized with the respect to the low temperature deposition prerequisite.