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Plasma-assisted molecular beam epitaxy of Sn-doped In2O3: Sn incorporation, structural changes, doping limits, and compensation



A comprehensive study of Sn doping in In2O3 during plasma-assisted molecular beam epitaxy (PA-MBE) is given, covering growth aspects and application-relevant aspects such as structural and transport properties. Single crystalline, (001) oriented indium oxide (In2O3) thin films were grown on Y-stabilized ZrO2(001) and systematically doped with 1018 cm−3 to 6 × 1021 cm−3 tin (Sn) by PA-MBE. The Sn incorporation was proportional to the Sn flux up to a Sn concentration of ≈1020 cm−3 indicating well-controllable doping in this regime. Toward higher Sn concentrations the Sn incorporation was increasingly impeded, which could be somewhat mitigated by increasing the oxygen-to-indium flux ratio. The surface faceting of undoped In2O3(001) during growth under oxygen rich conditions was prevented by doping to Sn concentrations math formula4×1020 cm−3. Up to Sn concentrations of 1.4 × 1021 cm−3 no detrimental effects on the film crystal quality were observed by X-ray diffraction, but concentrations math formula cm−3 resulted in structural deterioration with the formation of secondary crystalline phases. The electron concentration increased and resistivity decreased with increasing Sn concentration. The electron concentration was limited to ≈2 × 1021 cm−3 despite higher Sn concentrations and a minimum resistivity of 9 × 10−5 Ω cm was reached at a Sn concentration of ≈1021 cm−3. The highest electron concentrations and lowest resistivities were realized by a post-growth vacuum annealing to remove compensating acceptors. Guidelines to obtain low resistivity, high-quality indium tin oxide (ITO) films are given. Textured reference films grown on r-plane sapphire, Al2O3(10–12), showed very similar behavior in terms of incorporation, doping limit, and compensation, which indicates that our results are qualitatively not limited to single crystalline films.