COMPOSITE STRUCTURE OF ZINC OXIDE DEPOSITED EPITAXIALLY ON SAPPHIRE

1299237 Piezo-electric elements NORTH AMERICAN ROCKWELL CORP 24 Nov 1970 [24 Nov 1969] 55914/70 Heading H1E [Also in Division C7] A process for producing an epitaxial deposit of monocrystalline ZnO on a substrate of monocrystalline sapphire comprises heating a ZnO source material such that the ZnO vapour is transported to and epitaxially deposited on the substrate. The ZnO may be formed as a thin film or as a thick layer and the orientation of the ZnO single crystal is determined by the lattice orientation on the substrate deposition surface. The orientation of the C-axis can thus be varied over a wide range by varying the sapphire cut. Palladium-purified hydrogen at one atmosphere pressure is allowed to flow through a previously evacuated enclosure and powdered ZnO is heated in a quartz boat to a temperature of about 825‹ C., the boat supporting at a distance of 0À5 to 2À0 cm. above the ZnO the inverted substrate which is heated to a temperature of about 775‹ C. HCl gas may be introduced into the enclosure in a preferred concentration of about 2% of the total gas to clean the substrate before deposition. In a directional transducer in which the C-axis is parallel to the plane of the substrate, gold or aluminium electrodes may be evaporated on to the ZnO surface.