and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

A nitride semiconductor light-emitting device has an active layer of a single-quantum well structure or multi-quantum well made of a nitride semiconductor containing indium and gallium. A first p-type clad layer made of a p-type nitride semiconductor containing aluminum and gallium is provided in contact with one surface of the active layer. A second p-type clad layer made of a p-type nitride semiconductor containing aluminum and gallium is provided on the first p-type clad layer. The second p-type clad layer has a larger band gap than that of the first p-type clad layer. An n-type semiconductor layer is provided in contact with the other surface of the active layer.

Nitride semiconductor light emitting device

This study reviews densification behaviour, mechanical properties, thermal, and electrical conductivities of the ZrB2 ceramics and ZrB2-based composites. Hot-pressing is the most commonly used densification method for the ZrB2-based ceramics in historic studies. Recently, pressureless sintering, reactive hot pressing, and spark plasma sintering are being developed. Compositions with added carbides and disilicides displayed significant improvement of densification and made pressureless sintering possible at ≤2000 °C. Reactive hot-pressing allows in situ synthesizing and densifying of ZrB2-based composites. Spark plasma sintering displays a potential and attractive way to densify the ZrB2 ceramics and ZrB2-based composites without any additive. Young's modulus can be described by a mixture rule and it decreased with porosity. Fracture toughness displayed in the ZrB2-based composites is in the range of 2–6 MPa m1/2. Fine-grained ZrB2 ceramics had strengths of a few hundred MPa, which increased with the additions of SiC and MoSi2. The small second phase size and uniform distribution led to higher strengths. The addition of nano-sized SiC particles imparts a better oxidation resistance and improves the strength of post-oxidized ZrB2-based ceramics. In addition, the ZrB2-based composites showed high thermal and electrical conductivities, which decreased with temperature. These conductivities are sensitive to composition, microstructure and intergranular phase. The unique combinations of mechanical and physical properties make the ZrB2-based composites attractive candidates for high-temperature thermomechanical structural applications.

Densification of ZrB2-based composites and their mechanical and physical properties: A review

We demonstrate the fabrication of blue, green, and amber InGaN/GaN light-emitting diodes (LEDs) on semipolar {11-22} bulk GaN substrates. The {11-22}GaN substrates used in this study are produced by cutting out from a c-oriented GaN bulk crystal grown by hydride vapor epitaxy. The LEDs have a dimension of 320 ×320 µm2 and are packed in an epoxide resin. The output power and external quantum efficiency (EQE) at a driving current of 20 mA are 1.76 mW and 3.0%, respectively, for the blue LED, 1.91 mW and 4.1% for the green LED, and 0.54 mW and 1.3% for the amber LED. The maximum output powers obtained with a maximum current of 200 mA are 19.0 mW (blue), 13.4 mW (green), and 1.9 mW (amber), while the maximum EQEs are 4.0% at 140 mA (blue), 4.9% at 0.2 mA (green), and 1.6% at 1 mA (amber). It is confirmed that the emission light is polarized along the [1-100] direction, reflecting the low crystal symmetry of the {11-22} plane.

https://iopscience.iop.org/article/10.1143/JJAP.45.L659/pdf

Blue, Green, and Amber InGaN/GaN Light-Emitting Diodes on Semipolar {11-22} GaN Bulk Substrates

The present invention provides a method and apparatus for the production and labeling of objects in a manner suitable for the prevention and detection of counterfeiting. Thus, the system incorporates a variety of features that make unauthorized reproduction difficult. In addition, the present invention provides an efficient means for the production of labels and verification of authenticity, whereby a recording apparatus which includes a recording medium, having anisotrophic optical domains, along with a means for transferring a portion of the recording medium to a carrier, wherein a bulk portion of the recording medium has macroscopically detectable anisotrophic optical properties and the detecting apparatus thereon.

Authentication method and system

Zirconium diboride (ZrB2) has a hexagonal crystal structure with an in-plane lattice constant of 3.168 A, very close to that of GaN (3.189 A). It is a metalloid compound and a very good electrical conductor, with a resistivity of 4.6 µΩcm. We propose ZrB2 (0001) as an electrically conductive lattice-matched substrate for GaN. Firstly, bulk crystal growth of ZrB2 using a radio frequency (rf)-heated floating zone (FZ) method is presented. Relatively large crystals (10 mm×60 mm) were obtained using this method. The thermal expansion coefficient and thermal conductivity of ZrB2 were evaluated using this crystal. Characterization of ZrB2 (0001) mirror-polished substrate was carried out by optical microscopic examination and X-ray diffraction. Finally, the results of heteroepitaxial growth are briefly mentioned.

https://iopscience.iop.org/article/10.1143/JJAP.40.L1280/pdf

Zirconium Diboride (0001) as an Electrically Conductive Lattice-Matched Substrate for Gallium Nitride.

High-efficiency visible light emission in N-and-B-doped 6H-SiC epilayers was observed in photoluminescence measurements at room temperature. The orange-yellow light emission due to the recombination of donor-acceptor pairs (DAPs) has a broad spectrum with a peak wavelength of 576nm and a full width at half maximum of 110nm at 250K. The high B concentration of more than 1018cm−3 improves the emission efficiency of the DAP recombination at a high temperature. Compared with the photoluminescence spectrum of GaN at 10K, a high quantum efficiency of 95% was estimated for the highly B-doped sample. From time-resolved photoluminescence measurements, a DAP recombination time of 5.0ms was obtained, which is in good agreement with the calculated value by the rate equation with the assumption of a 95% internal quantum efficiency. This is quite promising as a light-emitting medium by optical pumping, as well as monolithic light sources combined with nitride-based light-emitting diodes grown on the DA-doped SiC epilayer.

/pdf/extremely-high-quantum-efficiency-of-donor-acceptor-pair-48a5nwb0es.pdf

Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC

We have proposed a novel solution with a use of a (308) 4H-SiC substrate for the reduction of internal polarization in the GaInN QWs. With changing the pressure at the initial stage of the nitride growth, two crystallographic orientations of the nitride layers could be switched. When the growth pressure was as high as 1013 hPa, the c-axis of the GaN is 54.7° tilted from the surface plane. On the other hand, the GaN having 7° tilted c-axis was dominant with the growth pressure of 100 hPa, where there is a relationship of SiC (0001) // GaN (101). We fabricated a LED on the (308) 4H-SiC substrate, where the c-axis orientation of 54.7° is tilted from the surface plane. The blue shift of the peak wavelength with increasing injection current was confirmed to be smaller than that of conventional LED grown along the c-axis on sapphire substrate. This small blue shift may be certain evidence that the GaInN active layer has small internal field as we expected. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN growth on (30&3macr;8) 4H‐SiC substrate for reduction of internal polarization

Disclosed is a phosphor which is excited by a long wavelength light source in the ultraviolet region or blue-violet visible region and mainly emits light in violet-blue-yellow-red visible region. Also disclosed is a low-cost light-emitting diode which is easily mounted and excellent in color rendering properties. This light-emitting diode does not have much color change due to radiation angle. A phosphor composed of SiC is characterized in that it is excited by an outside light source for emitting light and doped with N and at least one of B and Al.

Hiroyuki Kinoshita

Papers

Zirconium Diboride (0001) as an Electrically Conductive Lattice-Matched Substrate for Gallium Nitride.

Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC

GaN growth on (30&3macr;8) 4H‐SiC substrate for reduction of internal polarization

Phosphor and light-emitting diode

Growth of GaN on ZrB2 substrate by metal-organic vapor phase epitaxy