Domain Matching EpitaxialGrowth of In2O3Thin Films on α-Al2O3(0001).

Oxygen plasma assisted molecular beam epitaxy was usedto growthin films of In2O3on α-Al2O3(0001) over a range of substrate temperatures between300 and 750 °C. The crystal structures and morphologies wereexamined by X-ray diffraction, transmission electron microscopy, andatomic force microscopy. In all cases, the thermodynamically stablebody-centered cubic phase bcc-In2O3predominates in the films, with an epitaxial relationshipIn2O3(111)∥Al2O3(0001) and In2O3[11̅10]∥Al2O3[101̅0] determined by matching betweenthe sublattice oxygen atoms in Al2O3(0001) andthe In atoms in In2O3(111): this involves a30° rotation of the epilayer unit cell relative to that of thesubstrate and a 3:2 coincidence structure. A minority fraction ofmetastable rhombohedral rh-In2O3(0001) can be stabilized for substrate temperatures below 550 °Cdue to the similarity in the bonding symmetries between rh-In2O3and α-Al2O3. Despite the large mismatches between In2O3and Al2O3for the two epitaxial systems discussedabove (−13.2% for bcc-In2O3and .1% for rh-In2O3), we show that the epitaxy can be maintained in both cases by matchingsmall but different integral multiples of lattice planes of the In2O3and the substrate at the interface between thetwo. Thus, the strain is effectively released by dislocations localizedat the interface. This so-called domain matching epitaxial growthmode may open up a new route to fabrication of high-quality crystallinethin films of oxides on highly mismatched substrates. [ABSTRACT FROM AUTHOR]