We studied the crystallographic orientation of GaN nanostructures grown on Si(111) and Al 2 O 3 substrates. We evaluated Zr metal as a novel alternative to conventional buffer layers such as AlN and ZnO. One-dimensional structures (nanorods and nanoneedles) were grown by hydride vapor phase epitaxy at 650 and 600 C, and investigated using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. FE-SEM images showed that the GaN nanorods had a uniform diameter along the growth direction. XRD results indicated that the nanostructures had a hexagonal crystal structure, and pole figure measurements revealed that GaN nanostructures grown on the Si (111) substrate had a stronger c-axis crystallographic orientation than those grown on the Al 2 O 3 substrate.
A large threshold voltage shift (ÁV th ) seen in the nano-structured-thin film electroluminescent device (NS-TFELD) has been studied with simple formulas derived from the continuity of the electric flux density through the nano-structured dielectric layers. The electric fields in the emission layers and the tunneling rate from the interface state are dependent on the material and geometric parameters consisting of the emission layer, being different from those of the conventional TFELD. The estimates of ÁV th in NS-TFELD are in good agreement with the experimental data, implying that NS-TFELD operating at very low voltages will be realized.
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