Effect of In Composition on Two-Dimensional Electron Gas in Wurtzite AlGaN/InGaN Heterostructures

The effect of In composition on two-dimensional electron gas in wurtzite AlGaN/InGaN heterostructures is theoretically investigated. The sheet carrier density is shown to increase nearly linearly with In mole fraction x, due to the increase in the polarization charge at the AlGaN/InGaN interface. The electron sheet density is enhanced with the doping in the AlGaN layer. The sheet carrier density is as high as 3.7×1013 cm^-2 at the donor density of 10×1018 cm^-3 for the HEMT structure with x=0.3. The contribution of additional donor density on the electron sheet density is nearly independent of the In mole fraction.

Analysis of Optical Readout Sensitivity for Uncooled Infrared Detector

An optical readout uncooled infrared detector, employing a substrate-free focal plane array with pitch size 60μm, is established. The reflector deformation induced by the stress mismatching of the bi-layer structure is discussed and, in turn, a universal solution to determine both the optical readout sensitivity and the optimal filter position is found. By applying this solution, the optical readout sensitivity for the ideal plane reflector could theoretically increase by 80% as compared with the conventional operation, and the sensitivity loss caused by the reflector deformation can also be reduced to a reasonable level.

Optical Ring-Resonator Modulator Based on 0.8 μm CMOS Technology

Optical ring-resonator-based modulators are fabricated on the silicon-on-insulator material through the mature commercial 0.8μm complementary metal oxide semiconductor foundry. The device configuration is based on a single ring resonator coupled to one bus waveguide. The waveguide widths are about 1 μm. The p-i-n junctions are employed to inject currents. The experimental result shows that the ring resonators with the quality factor of above 40000 are obtained. The maximum extinction ratio of the modulators is larger than 10dB. The speed is tens of nanoseconds, and the corresponding injected current is smaller than 10 mA.

Derivative of Electron Density in Non-Equilibrium Green＇s Function Technique and Its Application to Boost Performance of Convergence

The non-equilibrium Green＇s function （NEGF） technique provides a solid foundation for the development of quantum mechanical simulators. However, the convergence is always of great concern. We present a general analytical formalism to acquire the accurate derivative of electron density with respect to electrical potential in the framework of NEGF. This formalism not only provides physical insight on non-local quantum phenomena in device simulation, but also can be used to set up a new scheme in solving the Poisson equation to boost the performance of convergence when the NEGF and Poisson equations are solved self-consistently. This method is illustrated by a simple one-dimensional example of an N＋＋ N＋ N＋＋ resistor. The total simulation time and iteration number are largely reduced.

Effects of End Termination on Electronic Transport in a Molecular Switch

Based on the non-equilibrium Green＇s function formalism and first-principles calculations, we investigate the electronic transport properties of an anthracene-based molecular switch with two carbon nanotube electrodes. Our results show that different terminations at the carbon nanotube end strongly affect the transport properties of the switch. In the case of H-termination the current at low biases is dominated by non-resonant tunneling. In the N-termination case the current at low biases is dominated by quasi-resonant tunneling and is increased by several orders of magnitude. The enhancement is discussed by the molecular projected self-consistent Hamiltonian level, transmission function, and local density of states.

Planar Metamaterial Absorber Based on Lumped Elements

We present the design of a planar metamaterial absorber based on lumped elements, which shows a wide-band polarization-insensitive and wide-angle strong absorption. This absorber consists of metal electric resonators, the dielectric substrate, the metal film and lumped elements. The simulated absorbances under two different loss conditions indicate that high absorbance in the absorption band is mainly due to lumped resistances. The simulated absorbances under three different load conditions indicate that the local resonance circuit （lumped resistance and capacitance） could boost up the resonance of the whole RLC circuit. The simulated voltage in lumped elements indicates that the transformation efficiency from electromagnetic energy to electric energy in the absorption band is high, and electric energy is subsequently consumed by lumped resistances. This absorber may have potential applications in many military fields.

AlGaN-Based Deep-Ultraviolet Light Emitting Diodes Fabricated on AlN/sapphire Template

We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.

Nondoped Electrophosphorescent Organic Light-Emitting Diodes Based on Platinum Complexes

An undoped electrophosphorescent organic light-emitting diode is fabricated using a pure platinum（Ⅱ） （2-phenylpyridinato-N, Ca） （3-benzoyl-camphor） [（ppy）pt（bcam）] phosphorescent layer acting as the emitting layer. A maximum power efficiency Tlp of 6.621m/W and current efficiency of 14.78 cd/A at 745 cd/m2 are obtained from the device. The roll-off percentage of ηp of the pure phosphorescent phosphor layer device is reduced to 5% at a current density of 20mA/cm2, which is about 11% for conventional phosphorescent devices. The low roll-off efficiency is attributed to the phosphorescent material, which has the molecular structure of a strong steric hindrance effect.

Equivalent Method of Solving Quantum Efficiency of Reflection-Mode Exponential Doping GaAs Photocathode

The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting LDE for LD, the equivalent quantum efficiency equation of the reflection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode.

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.

A 10Gb/s Directly-Modulated 1.3μm InAs/GaAs Quantum-Dot Laser

We demonstrate 10 Gb/s directly-modulated 1.3 μm InAs quantum-dot （QD） lasers grown on GaAs substrates by molecular beam epitaxy. The active region of the QD lasers consists of five-stacked InAs QD layers. Ridge-waveguide lasers with a ridge width of 4 μm and a cavity length of 600 μm are fabricated with standard lithography and wet etching techniques. It is found that the lasers emit at 1293 nm with a very low threshold current of 5 mA at room temperature. Furthermore, clear eye-opening patterns under 10 Gb/s modulation rate at temperatures of up to 50oC are achieved by the QD lasers. The results presented here have important implications for realizing low-cost, low-power-consumption, and high-speed light sources for next-generation communication systems.

Silicon Purification by a New Type of Solar Furnace

We propose a new method to reveal a direct transformation from solar energy to solar electricity. Instead of using electricity in the process, we use concentrated solar rays with a crucibleless process to upgrade metallurgical silicon into solar-grade silicon feedstock.

Numerical Simulations of Backward-to-Forward Leaky-Wave Antenna with Composite Right/Left-Handed Coplanar Waveguide

A composite right/left-handed （CRLH） coplanar waveguide （CPW） structure and its leaky-wave antenna （LWA） with continuous backward-to-forward scanning applications are proposed. The structure of the CRLH transmission line （TL） is composed of split-ring resonators （SRRs） for left-handed （LH） series capacitance and short-circuited stubs connected between the CPW central signal line and the ground for LH shunt inductance, while the unavoidable right-handed （RH） parasitic effects series inductance and shunt capacitance are generated by wave propagation through the host transmission line. The dispersion relations are calculated and compared with the equivalent circuit model method and 3D full-wave simulations, which can be used to determine the physical dimensions of the CRLH-CPW, such as in the balanced CRLH-TL case. As a main example, a CRLH-CPW-LWA operating from 1.67 GHz to 1.80 GHz with the dispersion characteristics of the balanced CRLH-TL case shows continuous leakage frequency band （fast wave region） from LH （phase constant β 〈0, .67〈f〈1.74 GHz） to RH （β〉0, 1.74〈f〈1.80 GHz） state through the transition frequency point （β=0, f=1.74 GHz）, whereas conventional LWAs operated in RH state only provide forward scanning capabilities （β〉0）.

Redox Controllable Switch of Crystalline Phase and Physical Property in SrVO_x Epitaxial Films

Transition-metal oxides have attracted much attention due to its abundant crystalline phases and intriguing physical properties. However, some of these compounds are difficult to be fabricated directly in film form due to the ease of valence variation of transition-metal elements.In this work, we reveal the reversible structural transition between SrVO3 and Sr2V2O7 films via thermal treatment in oxygen atmosphere or in vacuum. Based on this, Sr2V2O7 epitaxial films are successfully synthesized and studied. Property characterizations show that the semitransparent and metallic SrVO3 could reversibly switch into transparent and insulating Sr2V2O7, implying potential applications in controllable electronic and optical devices.

Metamorphic InGaAs p-i-n Photodetectors with 1.75 μm Cut-Off Wavelength Grown on GaAs

Top-illuminated metamorphic InGaAs p-i-n photodetectors （PDs） with 50% cut-off wavelength of 1.75 μm at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 × 10^-6 A/cm^2 at 0 V bias and 2.24 × 10^-4 A/cm^2 at a reverse bias of 5 V. At a wavelength of 1.55 μm, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 μm diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.

A Low-Voltage Silicon Light Emitting Device in Standard Salicide CMOS Technology

A silicon-based field emission light emitting diode for low-voltage operation is fabricated in the standard 0.35 μm 2P4M salieide complementary metal-oxide-semiconduetor （CMOS） technology. Partially overlapping p^＋ and n^＋ regions with a salicide block layer are employed in this device to constitute a heavily doped p^＋-n^＋ junction which has soft ＂knee＂ Zener breakdown characteristics, thus its working voltage can be reduced preferably below 5 V, and at the same time the power efficiency is improved. The spectra of this device are spread over 500nm to 1000nm with the main peak at about 722nm and an obvious red shift of the spectra peak is observed with the increasing current through the device. During the emission process, field emission rather than avalanche process plays a major role. Differences between low-voltage Zener breakdown emission and high-voltage avalanche breakdown emission performance are observed and compared.

Bending Efficiency of Bent Multiple-Slot Waveguides

The bending efficiency of three-dimensional bent multiple-slot waveguides is studied by applying a combined method of effective-index and modified transfer-matrix methods. The effects of asymmetric structure, asymmetric slots, and asymmetric middle strips on the bending efficiency are investigated. We show that the bending efficiency can be improved by the use of asymmetric structures and asymmetric middle strips. The bending efficiency of different slot waveguides （up to quintuple-slot structure） is compared. It is revealed that although the single-slot waveguide in general provides the lowest bending loss for the same waveguide parameters, it is possible that the multiple-slot waveguide can present a lower bending loss than the single-slot one.

Efficient Phase Locking of Fiber Amplifiers Using a Low-Cost and High-Damage-Threshold Phase Control System

We propose a low-cost and high-damage-threshold phase control system that employs a piezoelectric ceramic transducer modulator controlled by a stochastic parallel gradient descent algorithm. Efficient phase locking of two fiber amplifiers is demonstrated. Experimental results show that energy encircled in the target pinhole is increased by a factor of 1.76 and the visibility of the fringe pattern is as high as 90% when the system is in close-loop. The phase control system has potential in phase locking of large-number and high-power fiber laser endeavors.

Improved Microfluidic Coupled-Cavity Waveguides for Slow Light Transmission

We present a method based on the selective liquid infiltration in air holes to produce slow light in a coupled-cavity waveguide structured by two-dimensional photonic crystal and analyze the slow light propagation in the coupled-cavity waveguide with triangular lattice. The group velocity profile of different coupled-cavity waveguides, obtained by the selective liquid infiltration in the holes between the cavities in waveguide and the increased radius of the first row of holes adjacent to the waveguide, is evaluated by using both the plane-wave expansion method and a tight binding model. We determine the optimal parameters to reduce the group velocity. Using a simpler coupled-cavity waveguide structure we obtain smaller group velocity compared to most investigations.

Cryptanalysis and Improvement of Quantum Secret Sharing Protocol between Multiparty and Multiparty with Single Photons and Unitary Transformations

In a recent paper [Yan F L et al. Chin.Phys.Lett. 25（2008）1187], a quantum secret sharing the protocol between multiparty and multiparty with single photons and unitary transformations was presented. We analyze the security of the protocol and find that a dishonest participant can eavesdrop the key by using a special attack. Finally, we give a description of this strategy and put forward an improved version of this protocol which can stand against this kind of attack.