Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

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Luminescence properties of defects in GaN

Transparent conductors as solar energy materials: A panoramic review

https://www.andrew.cmu.edu/user/dl0p/laughlin/pdf/PMS.pdf

Amorphous and nanocrystalline materials for applications as soft magnets

Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

Optical Waveguide Theory

Single-crystalline GaN nanorods are formed on a sapphire substrate by hydride vapor phase epitaxy (HVPE). Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and cathodoluminescence (CL) techniques. The high density of straight and well-aligned nanorods with a diameter of 80–120 nm formed uniformly over the entire 2 in. sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the formed GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. We observed a higher CL peak position of individual GaN nanorods than that of bulk GaN as well as a blueshift of CL peak position with decreasing the diameter of GaN nanorods, which are attributed to quantum confinement effect in one-dimensional GaN nanorods. We demonstrate that the well-aligned, single-crystalline GaN nanorods with high density, high crystal quality, and good spatial uniformity are formed b...

Growth and characterization of single-crystal GaN nanorods by hydride vapor phase epitaxy

In this work, a highly efficient, flexible electro thermal heater based on highly conductive carbon nanotube functionalized cotton fabrics has been studied. Cotton fabrics were functionalized with single walled carbon nanotubes through a simple dip coating method. To explore their potential as heaters, electrothermal performances of the devices were studied in terms of applied voltage, heating rate and input power density. The highly flexible heater is constructed based on uniformly interconnected CNT networks, which yields an effective and rapid heating of the heater at low input power. The investigation results suggest promising applications of these devices in wearable electronics and beyond and they could also be woven into textile materials.

Highly efficient CNT functionalized cotton fabrics for flexible/wearable heating applications

The p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently Mn+ ions implanted. The properties of Mn+ ions-implanted GaN epilayers were investigated by optical and magnetic measurements. The results of photoluminescence measurement show that optical transitions related to Mn apparently appear at 2.5 eV and around 3.0 eV. It is confirmed that the photoluminescence peak at 2.5 eV is a donor–Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.

Optical and magnetic measurements of p-type GaN epilayers implanted with Mn+ ions

We have investigated the optical properties of dislocation-free vertical GaN nanorods grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy. The hexagonal shape nanorods with lateral diameters from 80 to 190 nm are obtained. They are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. Three distinct features are observed in photoluminescence. First, free exciton transition is observed at 3.477 eV for GaN nanorods of decreased diameter. Second, the photoluminescence spectra show an abnormal behavior with increasing temperature. The third feature is the size effect in that the PL peak energies are blueshifted with decreasing diameter of the GaN nanorod. The activation energy of the free exciton for the GaN nanorods with different diameters was evaluated.

T. W. Kang

Papers

Growth and characterization of single-crystal GaN nanorods by hydride vapor phase epitaxy

Highly efficient CNT functionalized cotton fabrics for flexible/wearable heating applications

Optical and magnetic measurements of p-type GaN epilayers implanted with Mn+ ions

Photoluminescence studies of GaN nanorods on Si (111) substrates grown by molecular-beam epitaxy

Electrochemical studies of spherically clustered MoS2 nanostructures for electrode applications