Fabrication of 2-Inch Free-Standing GaN Substrate on Sapphire With a Combined Buffer Layer by HVPE.

Free-standing GaN substrates are urgently needed to fabricate high-power GaN-based devices. In this study, 2-inch free-standing GaN substrates with a thickness of ~250 µm were successfully fabricated on double-polished sapphire substrates, by taking advantage of a combined buffer layer using hydride vapor phase epitaxy (HVPE) and the laser lift-off technique. Such combined buffer layer intentionally introduced a thin AlN layer, using a mix of physical and chemical vapor deposition at a relatively low temperature, a 3-dimensional GaN interlayer grown under excess ambient H2, and a coalescent GaN layer. It was found that the cracks in the epitaxial GaN layer could be effectively suppressed due to the large size and orderly orientation of the AlN nucleus caused by pre-annealing treatment. With the addition of a 3D GaN interlayer, the crystal quality of the GaN epitaxial films was further improved. The 250-µm thick GaN film showed an improved crystalline quality. The full width at half-maximums for GaN (002) and GaN (102), respectively dropped from 245 and 412 to 123 and 151 arcsec, relative to those without the 3D GaN interlayer. The underlying mechanisms for the improvement of crystal quality were assessed. This method may provide a practical route for fabricating free-standing GaN substrates at low cost with HVPE.

A Novel Nanorod Self-Assembled WO3 · H2O Spherical Structure: Preparation and Flexible Gas Sensor.

In this work, a novel WO³ · H²O spherical structure which was self-assembled by nanorods was achieved by using hydrothermal method. A comprehensive growth mechanism was proposed to explain the formation of three different type nanostructures. Flexible gas sensors were successfully fabricated based on such unique nanostructures. We found that these nanorods and nanoparticle's self-assembled spherical structure showed excellent gas response to ammonia. This result may provide great benefit potential to further study for the preparation and gas performance of such self-assembled structure of WO³ · H²O.

All-solution processed polymer light-emitting diode displays.

Adopting the emerging technology of printed electronics in manufacturing novel ultrathin flat panel displays attracts both academic and industrial interests because of the challenge in the device physics and the potential of reducing production costs. Here we produce all-solution processed polymer light-emitting diode displays by solution-depositing the cathode and utilizing a multifunctional buffer layer between the cathode and the organic layers. The use of ink-jetted conducting nanoparticles as the cathode yields high-resolution cathode patterns without any mechanical stress on the organic layers. The buffer layer, which offers the functions of solvent-proof electron injection and proper affinity, is fabricated by mixing the water/alcohol-soluble polymer and a curable epoxy adhesive. Our 1.5-inch polymer light-emitting diode displays are fabricated without any dead pixels or dead lines. The all-solution process eliminates the need for high vacuum for thermal evaporation of the cathode, which paves the way to industrial roll-to-roll manufacturing of flat panel displays.

High-performance, all-solution-processed organic nanowire transistor arrays with inkjet-printing patterned electrodes.

Organic nanowire (NW) transistor arrays with a mobility of as high as 1.26 cm(2)·V(-1)·S(-1) are fabricated by combining the dip-coating process to align the NW into arrays with the inkjet printing process to pattern the source/drain electrodes. A narrow gap of ~20 µm has been obtained by modifying the inkjet process. The all-solution process is proven to be a low-cost, high-yield, simple approach to fabricating high-performance organic NW transistor arrays over a large area.

In situ growing and patterning of aligned organic nanowire arrays via dip coating.

Aligned organic nanowire arrays are grown in situ and patterned via dip coating. By optimizing the stick-slip motion, the solvent evaporation conditions, and the solution concentration, parallel organic nanowire arrays with tunable length and desirable density and periodicity are directly grown and aligned on the substrate. Organic FETs based on the organic nanowire array have been successfully fabricated with a mobility of 1 x 10(-4) cm(2) .V(-1).s(-1).