silicon and gallium-nitride

The use of III-nitride-based light-emitting diodes (LEDs) is now widespread in applications such as indicator lamps, display panels, backlighting for liquid-crystal display TVs and computer screens, traffic lights, etc. To meet the huge market demand and lower the manufacturing cost, the LED industry is moving fast from 2 inch to 4 inch and recently to 6 inch wafer sizes. Although Al2O3 (sapphire) and SiC remain the dominant substrate materials for the epitaxy of nitride LEDs, the use of large Si substrates attracts great interest because Si wafers are readily available in large diameters at low cost. In addition, such wafers are compatible with existing processing lines for 6 inch and larger wafers commonly used in the electronics industry. During the last decade, much exciting progress has been achieved in improving the performance of GaN-on-Si devices. In this contribution, the status and prospects of III-nitride optoelectronics grown on Si substrates are reviewed. The issues involved in the growth of GaN-based LED structures on Si and possible solutions are outlined, together with a brief introduction to some novel in situ and ex situ monitoring/characterization tools, which are especially useful for the growth of GaN-on-Si structures.

Topics: Crystallization; Equipment Design; Equipment Failure Analysis; Gallium; Lighting; Nanoparticles; Nanotechnology; Optical Devices; Semiconductors; Silicon

The purpose of this study is to develop an in-bore radiofrequency (RF) power amplifier (RFPA) module with high power efficiency and density for use in parallel transmit (pTX) arrays at 3 Tesla.. The modules use a combination of current mode class D, class S, and class E amplifiers based on enhancement-mode gallium nitride-on-silicon field-effect transistors. Together the amplifiers implement envelope elimination and restoration to achieve amplitude modulation with high efficiency over a wide operating range. The static nonlinearity and power efficiency of the module were measured using pulsed RF measurements over a 37 dB dynamic range. Thermal performance was also measured with and without forced convection cooling.. The modules produces peak RF power up to 130 W with an overall efficiency of 85%. When producing 100 W RF pulses at a duty cycle of 10%, maximum junction temperatures did not exceed 80 °C, even without the use of heatsinks or forced convection.. The small size and low cost of the modules promise lower cost implementation of pTX systems compared with linear RFPAs located remotely. Further work must be done on control of the RF output in the presence of nonlinearities and coupling. Magn Reson Med 78:1589-1598, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Topics: Equipment Design; Gallium; Magnetic Resonance Imaging; Phantoms, Imaging; Radio Waves; Silicon; Transistors, Electronic

The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space.

Topics: Equipment Design; Equipment Failure Analysis; Gallium; Indium; Lighting; Materials Testing; Nanowires; Particle Size; Semiconductors; Silicon

Vertical GaN nanowires are grown in a self-induced way on a sputtered Ti film by plasma-assisted molecular beam epitaxy. Both in situ electron diffraction and ex situ ellipsometry show that Ti is converted to TiN upon exposure of the surface to the N plasma. In addition, the ellipsometric data demonstrate this TiN film to be metallic. The diffraction data evidence that the GaN nanowires have a strict epitaxial relationship to this film. Photoluminescence spectroscopy of the GaN nanowires shows excitonic transitions virtually identical in spectral position, line width, and decay time to those of state-of-the-art GaN nanowires grown on Si. Therefore, the crystalline quality of the GaN nanowires grown on metallic TiN and on Si is equivalent. The freedom to employ metallic substrates for the epitaxial growth of semiconductor nanowires in high structural quality may enable novel applications that benefit from the associated high thermal and electrical conductivity as well as optical reflectivity.

Topics: Gallium; Nanowires; Silicon; Titanium

Semipolar {101¯1} InGaN quantum wells are grown on (001) Si substrates with an Al-free buffer and wafer-scale uniformity. The novel structure is achieved by a bottom-up nano-heteroepitaxy employing self-organized ZnO nanorods as the strain-relieving layer. This ZnO nanostructure unlocks the problems encountered by the conventional AlN-based buffer, which grows slowly and contaminates the growth chamber.

Topics: Electrical Equipment and Supplies; Gallium; Nanotechnology; Nanotubes; Silicon

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow.

Topics: Equipment Design; Gallium; Indium; Light; Lighting; Luminescence; Microscopy, Fluorescence; Quantum Theory; Silicon; Temperature; X-Ray Diffraction

We have performed room-temperature time-resolved photoluminescence measurements on samples that comprise InGaN insertions embedded in GaN nanowires. The decay curves reveal non-exponential recombination dynamics that evolve into a power law at long times. We find that the characteristic power-law exponent increases with emission photon energy. The data are analyzed in terms of a model that involves an interplay between a radiative state and a metastable charge-separated state. The agreement between our results and the model points towards an emission dominated by carriers localized on In-rich nanoclusters that form spontaneously inside the InGaN insertions.

Topics: Crystallization; Gallium; Indium; Macromolecular Substances; Materials Testing; Molecular Conformation; Nanotubes; Particle Size; Silicon; Surface Properties

The toxicity of semiconductor materials can significantly hinder their use for in vitro and in vivo applications. Gallium nitride (GaN) is a material with remarkable properties, including excellent chemical stability. This work demonstrated that functionalized and etched GaN surfaces were stable in aqueous environments and leached a negligible amount of Ga in solution even in the presence of hydrogen peroxide. Also, GaN surfaces in cell culture did not interfere with nearby cell growth, and etched GaN promoted the adhesion of cells compared to etched silicon surfaces. A model peptide, "IKVAV", covalently attached to GaN and silicon surfaces increased the adhesion of PC12 cells. Peptide terminated GaN promoted greater cell spreading and extension of neurites. The results suggest that peptide modified GaN is a biocompatible and non-toxic material that can be used to probe chemical and electrical stimuli associated with neural interfaces.

Topics: Amino Acid Sequence; Animals; Biocompatible Materials; Gallium; Microscopy, Electron, Scanning; Molecular Sequence Data; PC12 Cells; Peptides; Rats; Silicon; Solutions; Spectrophotometry, Atomic; Surface Properties

We report on the achievement of, for the first time, InN/InGaN core/shell nanowire heterostructures, which are grown directly on Si(111) substrates by plasma-assisted molecular beam epitaxy. The crystalline quality of the heterostructures is confirmed by transmission electron microscopy, and the elemental mapping through energy dispersive x-ray spectrometry further reveals the presence of an InGaN shell covering the sidewall and top regions of the InN core. The optical characterizations reveal two emission peaks centered at ∼1685 nm and 1845 nm at 5 K, which are related to the emission from the InGaN shell and InN core, respectively. The InN/InGaN core/shell nanoscale heterostructures exhibit a very high internal quantum efficiency of ∼62% at room temperature, which is attributed to the strong carrier confinement provided by the InGaN shell as well as the nearly intrinsic InN core.

Topics: Catalysis; Crystallization; Gallium; Heavy Ions; Indium; Macromolecular Substances; Materials Testing; Molecular Conformation; Nanostructures; Particle Size; Porosity; Quantum Dots; Silicon; Surface Properties

A GaN/Si nanoheterostructure array was prepared by growing GaN nanostructures on silicon nanoporous pillar array (Si-NPA). Based on as-grown and annealed GaN/Si-NPA, two light-emitting diodes (LEDs) were fabricated. It was found that after the annealing treatment, both the turn-on voltage and the leakage current density of the nanoheterostructure varied greatly, together with the electroluminescence (EL) changed from a yellow band to a near infrared band. The EL variation was attributed to the radiative transition being transformed from a defect-related recombination in GaN to an interfacial recombination of GaN/Si-NPA. Ours might have provided an effective approach for fabricating GaN/Si-based LEDs with different emission wavelengths.

Topics: Equipment Design; Equipment Failure Analysis; Gallium; Hardness; Hot Temperature; Luminescent Measurements; Nanostructures; Nanotechnology; Silicon

Topics: Electric Conductivity; Gallium; Infrared Rays; Luminescent Measurements; Nanostructures; Porosity; Semiconductors; Silicon

Topics: Electronics, Medical; Gallium; Humans; Indium; Semiconductors; Silicon

We report an approach for growing aligned ZnO nanowire arrays with a high degree control over size, orientation, dimensionality, uniformity, and possibly shape. Our method combines e-beam lithography and a low temperature hydrothermal method to achieve patterned and aligned growth of ZnO NWs at <100degreesC on general inorganic substrates, such as Si and GaN, without using catalyst. This approach opens up the possibility of applying ZnO nanowires as sensor arrays, piezoelectric antenna arrays, two-dimensional photonic crystals, IC interconnects, and nanogenerators.

Topics: Catalysis; Cold Temperature; Crystallization; Gallium; Nanowires; Polymethyl Methacrylate; Silicon; X-Ray Diffraction; Zinc Oxide

GaN nanowires (NWs) have been grown on Si(111) substrates by plasma-assisted molecular beam epitaxy (PAMBE). The nucleation process of GaN-NWs has been investigated in terms of nucleation density and wire evolution with time for a given set of growth parameters. The wire density increases rapidly with time and then saturates. The growth period until the nucleation of new nanowires is terminated can be defined as the nucleation stage. Coalescence of closely spaced nanowires reduces the density for long deposition times. The average size of the well-nucleated NWs shows linear time dependence in the nucleation stage. High-resolution transmission electron microscopy measurements of alternating GaN and AlN layers give valuable information about the length and radial growth rates for GaN and AlN in NWs.

Topics: Crystallization; Gallium; Heavy Ions; Macromolecular Substances; Materials Testing; Molecular Conformation; Nanotechnology; Nanotubes; Particle Size; Silicon; Surface Properties

Doped EuO is an attractive material for the fabrication of proof-of-concept spintronic devices. Yet for decades its use has been hindered by its instability in air and the difficulty of preparing and patterning high-quality thin films. Here, we establish EuO as the pre-eminent material for the direct integration of a carrier-concentration-matched half-metal with the long-spin-lifetime semiconductors silicon and GaN, using methods that transcend these difficulties. Andreev reflection measurements reveal that the spin polarization in doped epitaxial EuO films exceeds 90%, demonstrating that EuO is a half-metal even when highly doped. Furthermore, EuO is epitaxially integrated with silicon and GaN. These results demonstrate the high potential of EuO for spintronic devices.

Topics: Computer Simulation; Crystallography, X-Ray; Europium; Gallium; Nanoparticles; Nanotechnology; Oxides; Semiconductors; Silicon

A new approach involving self-assembling block copolymer micellar templates and gas-phase reactions to synthesize arrays of monodisperse III-nitrides nanocrystals in the size range of 1-5 nm with uniform spacings between the nanoparticles is demonstrated. The photoluminescence emission spectra revealed the GaN nanocrystals are in the quantum-confined regime. This method not only offers great promise for the controlled synthesis of arrays of ternary III-nitride nanocrystals but may also enable doping in binary nitrides.

Topics: Crystallization; Gallium; Luminescence; Metal Nanoparticles; Micelles; Microscopy, Atomic Force; Microscopy, Electron, Transmission; Models, Chemical; Nanoparticles; Nanotechnology; Nitrogen; Oxygen; Photochemistry; Polymers; Silicon; Spectrophotometry; X-Ray Diffraction

In this work, the behaviors of cerebellar granule neurons prepared from 7-day-old Wistar rats on gallium nitride (GaN) were investigated. We believe that this is the first time that the GaN has been used as a substrate for neuron cultures to examine its effect on cell response in vitro. The GaN surface structure and its relationship with cells were examined by atomic force microscopy (AFM), metallography microscopy, scanning electron microscopy (SEM), lactate dehydrogenase (LDH) release and Western blot analysis. GaN is a so-called III-V compound semiconductor material with a wide bandgap and a relatively high bandgap voltage. Compared with silicon used for most neural chips, neurons seeded on GaN were able to form an extensive neuritic network and expressed very high levels of GAP-43 coincident with the neurite outgrowth. Therefore, the GaN structure may spatially mediate cellular response that can promote neuronal cell attachment, differentiation and neuritic growth. The favorable biocompatibility characteristics of GaN can be used to measure electric signals from networks of neuronal cells in culture to make it a possible candidate for use in a microelectrode array.

Topics: Animals; Cell Culture Techniques; Cell Differentiation; Cerebellum; Gallium; GAP-43 Protein; L-Lactate Dehydrogenase; Microarray Analysis; Neurons; Rats; Silicon

Doping of Si into GaN nanowires has been successfully attained via thermal evaporation in the presence of a suitable gas atmosphere. Analysis indicated that the Si-doped GaN nanowire is a single crystal with a hexagonal wurtzite structure, containing 2.2 atom % of Si. The broadening and the shift of Raman peak to lower frequency are observed, which may be attributed to surface disorder and various strengths of the stress. The band-gap emission (358 nm) of Si-doped GaN nanowires relative to that (370 nm) of GaN nanowires has an apparent blue shift (approximately 12 nm), which can be ascribed to doping impurity Si.

Topics: Gallium; Hot Temperature; Manufactured Materials; Materials Testing; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Models, Chemical; Nanotechnology; Nanotubes; Silicon; Spectrum Analysis, Raman; Temperature; Thermodynamics; X-Ray Diffraction

This study reports the synthesis of GaN nanoparticles having hexagonal structure by a simple technique of activated reactive evaporation with substrates kept at comparatively lower temperatures than usually reported. By varying the substrate temperature from 30 degrees C to 350 degrees C, it is possible to vary nanoparticle sizes from 5-30 nm. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirm the formation of GaN on quartz and silicon substrates at room temperature. The observed size dependent shift in energy position, large increase in full width at half maximum value of Ga 3d and N 1s X-ray photoelectron spectroscopy peaks and blue shift in the optical absorption edge are related to nanoparticle character.

Topics: Gallium; Microscopy, Electron, Transmission; Nanostructures; Nanotechnology; Nanotubes; Particle Size; Quartz; Silicon; Spectrometry, X-Ray Emission; Surface Properties; Temperature; X-Ray Diffraction; X-Rays

An in situ liquid gallium-gas interface chemical reaction route has been developed to synthesize semiconducting hollow GaN nanospheres with very small shell size by carefully controlling the synthesis temperature and the ammonia reaction gas partial pressure. In this process the gallium droplet does not act as a catalyst but rather as a reactant and a template for the formation of hollow GaN structures. The diameter of the synthesized hollow GaN spheres is typically 20-25 nm and the shell thickness is 3.5-4.5 nm. The GaN nanotubes obtained at higher synthesis temperatures have a length of several hundreds of nanometers and a wall thickness of 3.5-5.0 nm. Both the hollow GaN spheres and nanotubes are polycrystalline and are composed of very fine GaN nanocrystalline particles with a diameter of 3.0-3.5 nm. The room-temperature photoluminescence (PL) spectra for the synthesized hollow GaN spheres and nanotubes, which have a narrow size distribution, display a sharp, blue-shifted band-edge emission peak at 3.52 eV (352 nm) due to quantum size effects.

Topics: Ammonia; Crystallization; Gallium; Gases; Light; Microscopy, Electron, Transmission; Nanotechnology; Nanotubes; Pressure; Semiconductors; Silicon; Temperature; X-Ray Diffraction

Topics: Crystallization; Electrochemistry; Electronics; Gallium; Materials Testing; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Nanoparticles; Nanotechnology; Nanowires; Photochemistry; Plastics; Semiconductors; Silicon; Temperature