Chia-Ho Hsieh

Effect of N to Ga flux ratio on the GaN surface morphologies grown at high temperature by plasma-assisted molecular-beam epitaxy

The surface morphology of GaN epitaxial films grown by plasma-assisted molecular-beam epitaxy has been investigated. We found that the surface morphology was sensitive to the N to Ga flux ratio (N/Ga) when grown at a high temperature (i.e., 788 °C). At that temperature, we did not observe large sized Ga droplets on the surface even at Ga-rich conditions. Furthermore, we found a transition from two-dimensional (2D) to three-dimensional (3D) growth in the intermediate Ga-stable regime. The slope of the growth rate was different: Slope=(0.39±0.06) was observed in the 2D-growth mode and (0.14±0.03) in the 3D-growth mode. In the high N/Ga ratio, the total dislocation concentration was reduced, and the mixed threading dislocation concentration had a minimum value at N/Ga=22.5. By comparing with the Hall carrier concentration results, we found that the mixed threading dislocations influence the number of electronic carriers.

Line defects of M-plane GaN grown on γ-LiAlO2 by plasma-assisted molecular beam epitaxy

The edge and threading dislocations of M-plane GaN epilayers grown on γ-LiAlO2 have been studied by high-resolution transmission electron microscope. We found that edge dislocations were grown in [11¯00] direction while threading dislocations were generated along a1 or −a2 axes. We also observed a single stacking fault in the M-plane GaN epilayer.

Self-assembled GaN hexagonal micropyramid and microdisk

The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO2 by plasma-assisted molecular-beam epitaxy. It was found that the (0001¯) disk was established with the capture of N atoms by most-outside Ga atoms as the (1×1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.

Self-Assembled c-Plane GaN Nanopillars on γ-LiAlO2 Substrate Grown by Plasma-Assisted Molecular-Beam Epitaxy

We have grown M-plane GaN films with self-assembled C-plane GaN nanopillars on a γ-LiAlO2 substrate by plasma-assisted molecular-beam epitaxy. The diameters of the basal plane of the nanopillars are about 200 to 900 nm and the height is up to 600 nm. The formation of self-assembled c-plane GaN nanopillars is through nucleation on hexagonal anionic bases of γ-LiAlO2. Dislocation defects were observed and analyzed by transmission electron microscopy. From the experimental results, we developed a mechanism underlying the simultaneous growth of three-dimensional c-plane nanopillars and two-dimensional M-plane films on a γ-LiAlO2 substrate.

Self-confined GaN heterophased quantum wells

Wurtzite/zinc-blende/wurtzite GaN heterophased quantum wells (QWs) were grown by plasma-assisted molecular beam epitaxy. A self-assembling mechanism was used to simulate the heterophased QW, in which a wurtzite/zinc-blende phase transition was created by rotating the threefold symmetric N-Ga vertical bond 60°. The GaN heterophased QW was attested by transmission electron microscopy, selective area electron diffraction and cathodoluminescence measurements.

Characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy

The characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy on LiAlO2 substrate was studied by cathodoluminescence and photoluminescence measurements. We demonstrated that the cathodoluminescence from oblique semi-polar surfaces of mushroom-shaped GaN was much brighter than that from top polar surface due to the reduction of polarization field on the oblique semi-polar surfaces. It implies that the oblique semi-polar surface is superior for the light-emitting surface of wurtzite nano-devices.

Current Development and Patents on High-Brightness White LED for Illumination

In this paper, we reviewed the current development and patents for the application of high-brightness and high-efficiency white light-emitting diode (LED). The high-efficiency GaN nanostructures, such as disk, pyramid, and rod were grown on LiAlO(2) substrate by plasma-assisted molecular-beam epitaxy, and a model was developed to demonstrate the growth of the GaN nanostructures. Based on the results, the GaN disk p-n junction was designed for the application of high brightness and high efficiency white LED.