Chen-Chi Yang

Spin splitting in AlxGa1―xN/GaN quasiballistic quantum wires

We have observed beating Shubnikov–de Haas oscillations in Al0.18Ga0.82N/GaN [112¯0]-direction quantum wires grown on (0001) sapphire. The spin-splitting energy, (2.4±0.3) meV for 200 nm wire, was suppressed to (1.2±0.3) meV for 100 nm wire and smeared by the scattering from edge states and intersubbands. The spin splitting of Rashba effect can be used to control the differential phase shift of spin-polarized electrons when a gate bias is applied to a nanometer arm of quantum ring. Based on the results of spin-splitting for the [112¯0]-direction AlxGa1−xN/GaN nanowire, the spin splitting of one-dimensional electron system in AlGaN/GaN nanowire can be applied to a low-power consuming quantum-ring interferometer.

Growth of InN hexagonal microdisks

InN hexagonal thin wurtzite disks were grown on γ-LiAlO2 by plasma-assisted molecular-beam epitaxy at low temperature (470oC). The (0001¯) InN thin disk was established with the capture of N atoms by the β¯-dangling bonds of most-outside In atoms, and then the lateral over-growth of the In atoms were caught by the β¯-dangling bonds of the N atoms. From the analyses of high-resolution transmission electron microscopy, the lateral over-grown width was extended to three unit cells at [11¯00]InN direction for a unit step-layer, resulting in an oblique surface with 73o off c-axis.

Growth and Characteristics of High-quality InN by Plasma- Assisted Molecular Beam Epitaxy

The high-quality InN epifilms and InN microdisks have been grown with InGaN buffer layers at low temperatures by plasma-assisted molecular beam epitaxy. The samples were analyzed using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence. The characteristics of the InN epifilms and InN microdisks were studied, and the role of InGaN buffer was evaluated.

Growth of InGaN/GaN quantum wells with graded InGaN buffer for green-to-yellow light emitters

We have studied the growth of high-indium-content In x Ga1− x N/GaN double quantum wells (QWs) for yellow and green light emitters by plasma-assisted molecular beam epitaxy at a low substrate temperature (570 °C). By introducing a graded In y Ga1− y N buffer layer, the PL intensity of QWs can be increased sixfold compared with that of the original structure. In addition, the indium content in InGaN QWs was increased owing the prolonged growth time of the graded In y Ga1− y N buffer layer. After adjusting to optimal growth conditions, we achieved In x Ga1− x N/GaN QWs with x = 0.32. Photoluminescence measurements showed that the emission wavelength from In x Ga1− x N/GaN QWs was 560 nm (2.20 eV). The optimal condition for the gradient In y Ga1− y N buffer layer was obtained for light emission from green to yellow.

GaN and InN Hexagonal Microdisks

The high-quality GaN microdisks with InGaN/GaN quantum wells (QWs) and InN microdisks were grown on γ-LiAlO 2 substrates by plasma-assisted molecular beam epitaxy (PA-MBE). The samples were analysed using scanning electron microscopy, X-ray diffraction, photoluminescence, cathodoluminescence and high-resolution transmission electron microscope. The characteristics of the GaN microdisks and InN microdisks were studied and the effect of growth temperature was evaluated.

Finite growth of InGaN/GaN triple-quantum-well microdisks on LiAlO2 substrate

We have grown high-quality InxGa1-xN/GaN triple-quantum-well microdisks on LiAlO2 substrate by plasma-assisted molecular beam epitaxy. The InxGa1-xN/GaN microdisk with a hexagonal shape of oblique face 28o-angle off c-axis was achieved. The mechanism of the termination of awl-shaped growth and the growth rates of GaN-barrier and InxGa1-xN-well were evaluated and confirmed with the triple quantum wells. Based on the growth rates and 28o-angle geometric shape, one can control the finite size of InGaN/GaN microdisks by plasma-assisted molecular beam epitaxy.