In this paper, we report the fabrication of porous and crystalline tin-doped indium oxide (ITO) thin films at room temperature by ion beam sputtering deposition at oblique angles using either argon or xenon ions. Deep insights into these systems are provided by coupling nanostructural (scanning and transmission electron microscopies, X-ray diffraction) and optical (spectroscopic ellipsometry, spectral reflectometry) characterizations. This original approach allows extracting important features of the films (porosity, refractive indexes, in-grain carrier densities, and mobilities) not easy to reach locally by other techniques. We propose a model decomposing the complex film's nanostructure into two layers presenting different electro-optical properties, which are attributed to the shadowing effect, but also to the presence of growth defects and impurities due to the atomic peening. In particular, we demonstrate that ITO films deposited with Xe present a better crystallinity and larger porosity, providing superior in-grain carrier transport and offering more flexibility to design broad-band low-reflectivity surfaces. These results widen the possibilities to engineer transparent and conductive thin films at room temperature with enhanced properties, especially in the near-infrared range where oblique angle deposition allows a reduction of reflectivity even at high doping.
Amorphous gallium oxide thin films were grown by plasma-enhanced atomic layer deposition on (100) silicon substrates from trimethylgallium Ga(CH3)3 precursor and oxygen plasma. At 200 °C, the growth per cycle is in the range of 0.65–0.70 Å for O2 plasma exposure times ranging from 3 up to 30 s during each cycle. The effect of O2 plasma exposure times on the interfacial SiOx regrowth and the electrical properties was investigated. In situ spectroscopic ellipsometry shows that the SiOx regrowth occurs during the first three cycles and is limited to 0.27 nm for plasma times as long as 30 s. Increasing the O2 plasma exposure during each ALD cycle leads to a drastic decrease in the leakage current density (more than 5 orders of magnitude for 30 nm films), which is linked to the suppression of oxygen vacancy states as evidenced by spectroscopic ellipsometry. Interestingly, an increase in the dielectric constant with increasing O2 plasma exposure time is observed, reaching a value of εr∼14.2, larger than that of single crystalline β-Ga2O3. This study highlights the crucial role of oxygen plasma exposure time in the control and tuning of the electrical properties of amorphous gallium oxide films.
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