A near-UV emitting diode was fabricated by successive heteroepitaxial growth of In2O3:Sn(ITO), n-electrode, n-ZnO, and p-SrCu2O2 (SCO) on an extremely flat surface of yttria-stabilized ZrO2 single crystalline substrate using a pulsed-laser deposition technique. Upon current injection at room temperature, the resulting diode emitted near-UV light with a peak at 382 nm. The threshold voltage for emission was ∼ 3 V, which is in agreement with the energy difference between the ZnO donor level and the SCO acceptor level. The epitaxial relationship between SCO and ZnO depends on the deposition temperature of SCO on ZnO. The inhomogeneity of the SCO crystal was improved by raising the deposition temperature from 350°C to 600°C. The threshold current for near-UV emission from the diode fabricated by deposition of the SCO film at 600°C was reduced to ∼ 1/5 of that at 350°C. A reason why this heteroepitaxial growth occurs for oxides with large lattice misfit is explained in terms of the high ionicity of chemical bonds in oxides.
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