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Crystallisation phenomena of In₂O₃:H films

: Muydinov, R.; Steigert, A.; Wollgarten, M.; Michalowski, P.; Bloeck, U.; Pflug, A.; Erfurt, D.; Klenk, R.; Körner, S.; Lauermann, I.; Szyszka, B.

Volltext ()

Materials 12 (2019), Nr.2, Art. 266, 20 S.
ISSN: 1996-1944
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IST ()
In₂O₃-H; thin film; crystallization; TCO; high mobility

The crystallisation of sputter-deposited, amorphous In₂O₃:H films was investigated. The influence of deposition and crystallisation parameters onto crystallinity and electron hall mobility was explored. Significant precipitation of metallic indium was discovered in the crystallised films by electron energy loss spectroscopy. Melting of metallic indium at ~160 °C was suggested to promote primary crystallisation of the amorphous In₂O₃:H films. The presence of hydroxyl was ascribed to be responsible for the recrystallization and grain growth accompanying the inter-grain In-O-In bounding. Metallic indium was suggested to provide an excess of free electrons in as-deposited In₂O₃: and In₂O₃:H films. According to the ultraviolet photoelectron spectroscopy, the work function of In₂O₃:H increased during crystallisation from 4 eV to 4.4 eV, which corresponds to the oxidation process. Furthermore, transparency simultaneously increased in the infrared spectral region. Water was queried to oxidise metallic indium in UHV at higher temperature as compared to oxygen in ambient air. Secondary ion mass-spectroscopy results revealed that the former process takes place mostly within the top ~50 nm. The optical band gap of In₂O₃:H increased by about 0.2 eV during annealing, indicating a doping effect. This was considered as a likely intra-grain phenomenon caused by both (In⁰)o•• and (OH⁻)o• point defects. The inconsistencies in understanding of In₂O₃:H crystallisation, which existed in the literature so far, were considered and explained by the multiplicity and disequilibrium of the processes running simultaneously.