Research topic 1
Catalyst free 1D nanostructure growth
Metalorganic vapor-phase epitaxial growth of vertically well-aligned ZnO nanorods
We report metalorganic vapor-phase epitaxial growth and structural and photoluminescent characteristics of ZnO nanorods. The nanorods were grown on Al2O3(001) substrates at 400 °C without employing any metal catalysts usually needed in other methods. Electron microscopy revealed that nanorods with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates. The mean diameter of the nanorods is as narrow as 25 nm. In addition, x-ray diffraction measurements clearly show that ZnO nanorods were grown epitaxially with homogeneous in-plane alignment as well as a c-axis orientation. More importantly, from photoluminescence spectra of the nanorods strong and narrow excitonic emission and extremely weak deep level emission were observed, indicating that the nanorods are of high optical quality.
Electroluminescence in n-ZnO Nanorod Arrays Vertically Grown on p-GaN
Electroluminescent (EL) devices have been fabricated using n-ZnO nanorod arrays grown on p-GaN epilayers. Simple heteroepitaxial growth yields vertically aligned ZnO nanorods with an abrupt interface on GaN. The p?n heterojunction EL device shows a high current density and strong electroluminescence even at a reverse-bias voltage of 3 V.
Quantum Confinement Observed in ZnO/ZnMgO Nanorod Heterostructures
Multiple quantum well nanorods have been fabricated via heteroepitaxial growth of ZnO and ZnMgO (see Figure and also cover). Simple yet accurate thickness control allows the realization of nanosized well structures in individual nanorods that are tunable through the effects of quantum confinement. This approach should be readily extendible to other heteroepitaxial semiconductor nanorods.
Shape-Controlled Nanoarchitectures Using Nanowalls
A novel method for shaping and positioning ZnO nanoarchitectures using conventional lithography and catalyst-free metal organic vapor-phase epitaxy is demonstrated. Nanowalls and nanotubes of desired shapes and arrangements can be grown heteroepitaxially on Si substrates, and their electron-emission characteristics were optimized by changing their diameter and spacing. This method can be readily expanded to create many artificial 1D and 2D structures, as required for various device applications.
GaN/In1-xGaxN/GaN/ZnO nanoarchitecture light emitting diode microarrays
We studied the fabrication and electroluminescent EL characteristics of GaN/In1?xGaxN/GaN/ZnO nanoarchitecture light emitting diode (LED) microarrays consisting of position-controlled GaN/ZnO coaxial nanotube heterostructures. For the fabrication of nanoarchitecture LED arrays, n-GaN, GaN/In0.24Ga0.76N multiquantum well (MQW) structures and p-GaN layers were deposited coaxially over the entire surface of position-controlled ZnO nanotube arrays grown vertically on c-plane sapphire substrates. The nanoarchitecture LEDs exhibited strong green and blue emission from the GaN/GaN/In0.24Ga0.76N MQWs at room temperature. Furthermore, the origins of dominant EL peaks are also discussed.
Visible-Color-Tunable Light-Emitting Diodes
Visible-color-tunable light-emitting diodes (LEDs) with electroluminescent color that changes continuously from red to blue by adjusting the external electric bias are fabricated using multifacetted GaN nanorods with anisotropically formed 3D InGaN multiple-quantum wells. Monolithically integrated red, green, and blue LEDs on a single substrate, operating at a fixed drive current, are also demonstrated for inorganic full-color LED display applications.
