NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. This work reports the controlling of conductivity and increase of work functions by Li doping.
Oxygen plasma assisted molecular beam epitaxy was used
to grow
thin films of In2O3 on α-Al2O3(0001) over a range of substrate temperatures between
300 and 750 °C. The crystal structures and morphologies were
examined by X-ray diffraction, transmission electron microscopy, and
atomic force microscopy. In all cases, the thermodynamically stable
body-centered cubic phase bcc-In2O3 predominates in the films, with an epitaxial relationship
In2O3(111)∥Al2O3(0001) and In2O3 [11̅10]∥Al2O3[101̅0] determined by matching between
the sublattice oxygen atoms in Al2O3(0001) and
the In atoms in In2O3(111): this involves a
30° rotation of the epilayer unit cell relative to that of the
substrate and a 3:2 coincidence structure. A minority fraction of
metastable rhombohedral rh-In2O3(0001) can be stabilized for substrate temperatures below 550 °C
due to the similarity in the bonding symmetries between rh-In2O3 and α-Al2O3. Despite the large mismatches between In2O3 and Al2O3 for the two epitaxial systems discussed
above (−13.2% for bcc-In2O3 and +15.1% for rh-In2O3), we show that the epitaxy can be maintained in both cases by matching
small but different integral multiples of lattice planes of the In2O3 and the substrate at the interface between the
two. Thus, the strain is effectively released by dislocations localized
at the interface. This so-called domain matching epitaxial growth
mode may open up a new route to fabrication of high-quality crystalline
thin films of oxides on highly mismatched substrates.
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