Abstract
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 infraredspectral 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.
Highlights
Hydrogen doped indium oxide (In2 O3 :H) films demonstrate an electron Hall mobility of over 100 cm2 /Vs [1,2]
In oxygen-deficient In2 O3 films, metallic indium may form as a result of oversaturation by cooling down after deposition at elevated temperature [36]
According to the impedance measurements performed on In2 O3 polycrystalline samples, their reduction in dry hydrogen results in a slow resistance decline, starting already at room temperature
Summary
Hydrogen doped indium oxide (In2 O3 :H) films demonstrate an electron Hall mobility (μe ) of over 100 cm2 /Vs [1,2]. Such outstanding property can be achieved if the In2 O3 film is deposited in an amorphous state and subsequently crystallised at T > 160 ◦ C. It is widely accepted in literature that the n-type doping of crystalline In2 O3 is related to the hydrogen incorporation. The question of whether we deal with so-called plasma damage still remains This negative effect of the accelerated O− ions largely determines electrical properties and their spatial deviations over the film [12,13]. We attempted to compose a full puzzle from all these data and understand this material better
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