ZnO and related materials have excellent optical and electronic properties, and recent advancements in epitaxial growth technique have spurred the investigation of these materials for applications
such as ultraviolet light-emitting diodes and invisible transistors. Although reliable technique for p-type doping
into ZnO is not yet completed, the crystalline quality and materials purity is now approaching ultimate limits−
the fractional quantum Hall effect has been observed in ultraclean ZnO/MgZnO interfaces. The majority of the
applications presently envisaged can essentially be realized if single-crystalline layers glow on low-cost glass
and polymer substrates in a fashion of graphoepitaxy. The notion of graphoepitaxy has been applied for many classes of materials, including semiconductors, metals, molecular compounds, and alkali halides. A rational mechanism of crystal orientations is induced by the fact that nucleation occurs under geometric constraint in a grating lithographically fabricated on the glass surface. Here we study this for the ionic oxide semiconductor, hexagonal ZnO on a quartz substrate with a square-wave relief grating structure. The epitaxial structure was obtained by two-step growth; pulsed-laser deposition (PLD) of a c-axis oriented, homogeneous nucleation
layer, followed by mist chemical vapor deposition (Mist CVD) of an in-plane oriented, a few microns domains (a
few microns). Surprisingly, rotational symmetry of the domains was found to be twisted by 90º from right angles commonly found in graphoepitaxy (i.e., crystal facet m-planes parallel to the side walls). We investigated surface morphology for the growth-interrupted films to identify that the m-plane facets indeed
appeared perpendicular to side walls. The details of novel selection rule of the domain formation and the electronic properties of the obtained films will be presented.
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