Jie Song

Multi-color broadband visible light source via GaN hexagonal annular structure

Multi-color and broadband visible emission was realized thorough the hexagonal annular structure of GaN. The annular structure fabricated by selective-area growth emitted purple, blue and green color-emission from the multi-facets. The hexagonal annular structure provided various sidewalls of {101} and {112} semi-polar facets, and (0001) polar facet. From the cathodoluminescence study, the (0001) plane had the longest wavelength of 525 nm, and the {101} facet of 440 nm peak wavelength had longer wavelength emission than the {112} of 412 nm peak wavelength. The origin of longer wavelength emission of {101} was mostly due to high In-composition, as well as slightly larger well thickness, which means that {101} facet has higher In-incorporation efficiency. Various In-composition of each facet provided multi-color and broadband emission with the international commission on illumination (CIE) of (0.22, 0.45) and high emission efficiency. The hexagonal annular structure becomes building blocks for highly efficient broadband visible lighting sources.

Wide bandgap III-nitride nanomembranes for optoelectronic applications

Single crystalline nanomembranes (NMs) represent a new embodiment of semiconductors having a two-dimensional flexural character with comparable crystalline perfection and optoelectronic efficacy. In this Letter, we demonstrate the preparation of GaN NMs with a freestanding thickness between 90 to 300 nm. Large-area (>5 × 5 mm(2)) GaN NMs can be routinely obtained using a procedure of conductivity-selective electrochemical etching. GaN NM is atomically flat and possesses an optical quality similar to that from bulk GaN. A light-emitting optical heterostructure NM consisting of p-GaN/InGaN quantum wells/GaN is prepared by epitaxy, undercutting etching, and layer transfer. Bright blue light emission from this heterostructure validates the concept of NM-based optoelectronics and points to potentials in flexible applications and heterogeneous integration.

Evolutionary selection growth: towards template-insensitive preparation of single-crystal layers.

IO N Epitaxy of semiconductor layers has enabled the development of the contemporary optoelectronic and microelectronic industry. A fundamental prerequisite in epitaxy is the availability of crystalline substrates having a reasonable match in crystallographic structure and atomic registry. The freedom to prepare single crystalline layers on amorphous or polycrystalline substrates is a tantalizing yet conceptually daunting quest: on a surface with no long-range atomic ordering, how can nucleation, incorporation, and growth proceed to produce a macroscopic-scale crystal? Artifi cial epitaxy , or graphoepitaxy , [ 1 ] resorts to surface patterning, typically through electron-beam, interferometric, or photolithography, to create geometric boundary conditions on the length scale of nuclei so their orientations can be infl uenced, if not dictated, by the shape of the moulds. [ 2 , 3 ] With all the advances in growth and lithography techniques since then however, graphoepitaxy has not produced the level of control required by modern device applications. Here, we demonstrate single-crystal growth on amorphous oxide by exploiting a phenomenon in material deposition: evolutionary selection growth. [ 4 ] With the successive applications of evolutionary selection (ES) along two perpendicular axes, we remove the degrees of freedom in grain orientations, resulting in the preparation of single-crystalline GaN on a SiO 2 /Si(100) template. The conceptual model of ES is confi rmed by the modeling of growth dynamics and provides a universal procedure in forming crystalline layers on amorphous substrates. It is intriguing to note that the deposition of thin fi lms on amorphous substrates does not necessarily, as one might expect, always lack order and symmetry. There are instances that textured thin fi lms can be formed spontaneously on arbitrary substrates. [ 5– 8 ] These textured fi lms consist of fi brous grains with a preferential axis oriented along the growth direction yet with no in-plane (transverse) alignment. The origin of the spontaneous formation of orientation with the increase of fi lm thickness was explained by the ES model. [ 4 ] According to this model the randomly oriented nuclei grow and undergo a competitive, geometric selection process; nuclei with their fastest growing axis oriented obliquely from surface normal are blocked (or fi ltered out) by adjacent nuclei with better on-axis alignment, thus creating a “survival of the fastest” phenomenon ( Figure 1 a). While these textured thin fi lms are in essence

Semipolar (20 2 ¯ 1) GaN and InGaN quantum wells on sapphire substrates

Here, we demonstrate a process to produce planar semipolar (20 2¯1) GaN templates on sapphire substrates. We obtain (20 2¯1) oriented GaN by inclined c-plane sidewall growth from etched sapphire, resulting in single crystal material with on-axis x-ray diffraction linewidth below 200 arc sec. The surface, composed of (10 1¯1) and (10 1¯0) facets, is planarized by the chemical-mechanical polishing of full 2 in. wafers, with a final surface root mean square roughness of <0.5 nm. We then analyze facet formation and roughening mechanisms on the (20 2¯1) surface and establish a growth condition in N2 carrier gas to maintain a planar surface for further device layer growth. Finally, the capability of these semipolar (20 2¯1) GaN templates to produce high quality device structures is verified by the growth and characterization of InGaN/GaN multiple quantum well structures. It is expected that the methods shown here can enable the benefits of using semipolar orientations in a scalable and practical process and can...

Growth, structural and optical properties of ternary InGaN nanorods prepared by selective-area metalorganic chemical vapor deposition

Ternary InGaN nanorods were prepared on dielectric-masked nano-holes with selective area metalorganic chemical vapor deposition. To overcome the tendency for random nucleation of GaN at low temperatures, a pulsed growth procedure was introduced to enhance the diffusion length of Ga adatoms on SiO2, resulting in good selectivity at typical temperature ranges for InGaN. Photoluminescence from the InGaN nanorods can be tuned from near ultraviolet (400 nm) to blue-green (~500 nm). Microstructural properties were characterized by transmission electron microscopy; threading dislocations from the underlying GaN template were terminated at the nanorod/template interface, resulting in dislocation-free nanorods. The height of dislocation-free InGaN nanorods is about 150 nm, which is much larger than the critical thickness for the onset of misfit dislocations in planar InGaN growth with typical thickness of less than 10 nm for an indium composition between 10 and 20%. The composition profile of In along the growth direction was examined by energy dispersive x-ray spectroscopic mapping and line scan. Oscillations of In composition along the growth direction were observed and are likely due to the kinetic competition between In and Ga adatoms. These InGaN nanorods are expected to be useful as templates for growing higher In composition nano-light-emitting diodes.

Semipolar (202̅1̅) GaN and InGaN Light-Emitting Diodes Grown on Sapphire

We have demonstrated growing uniform and purely nitrogen polar semipolar (202̅1̅) GaN epilayers on 2 in. patterned sapphire substrates. The as-grown surface of (202̅1̅) GaN is composed of two stable facets: (101̅0) and (101̅1̅). A chemical mechanical polishing process was further used to planarize the surface with a final surface root-mean-square roughness of less than 1.5 nm over an area of 10 × 10 μm2. InGaN light-emitting diodes were grown on a polished (202̅1̅) GaN/sapphire template with an electroluminescence emission at around 490 nm. Our work exhibits the potential to produce high-quality nitrogen-polar semipolar GaN templates and optoelectronic devices on large-area sapphire substrates with economical feasibility.

Using the Evolutionary Selection Principle in Selective Area Growth to Achieve Single-Crystalline GaN on SiO2

Conventional epitaxial techniques requires single crystalline substrates to form semiconductor material of desired material quality for device applications. The use of amorphous substrates, in many applications, provides an opportunity to consider new materials and designs, which can fundamentally alter the performance, functionality and/or cost limitations of many optoelectronic devices. Here, a growth process is described to achieve single crystalline GaN material on amorphous SiO2. The evolutionary selection principle in crystal growth is the basis of this technique, and the mechanism is described and analyzed in detail. It is expected that this process can be extended to other semiconductor and substrate combinations, allowing heterogenous integration with functional substrates to produce new classes of semiconductor devices.