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Plasma‐assisted molecular beam epitaxy of Sn‐doped In 2 O 3 : Sn incorporation, structural changes, doping limits, and compensation
Author(s) -
Bierwagen Oliver,
Speck James S.
Publication year - 2014
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201330224
Subject(s) - molecular beam epitaxy , doping , materials science , analytical chemistry (journal) , electrical resistivity and conductivity , annealing (glass) , indium , tin , electron diffraction , electron mobility , epitaxy , thin film , indium tin oxide , crystallography , nanotechnology , chemistry , diffraction , optoelectronics , metallurgy , optics , layer (electronics) , physics , engineering , chromatography , electrical engineering
A comprehensive study of Sn doping in In 2 O 3 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 (In 2 O 3 ) thin films were grown on Y‐stabilized ZrO 2 (001) and systematically doped with 10 18 cm −3 to 6 × 10 21 cm −3 tin (Sn) by PA‐MBE. The Sn incorporation was proportional to the Sn flux up to a Sn concentration of ≈10 20 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 In 2 O 3 (001) during growth under oxygen rich conditions was prevented by doping to Sn concentrations ≳ 4×10 20 cm −3 . Up to Sn concentrations of 1.4 × 10 21 cm −3 no detrimental effects on the film crystal quality were observed by X‐ray diffraction, but concentrations ≳ 4.9 × 10 21 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 × 10 21 cm −3 despite higher Sn concentrations and a minimum resistivity of 9 × 10 −5 Ω cm was reached at a Sn concentration of ≈10 21 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, Al 2 O 3 (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.