Detection band expansion by independently tunable double resonances in a long-wavelength dual-color QWIP.

Multi-resonance light coupling management is a promising way to expand the operating spectral ranges of optoelectronic devices. The classical strategies are either lack of independent tunability for each resonance or involved with complex fabrication. Here, we propose a new scheme for expanding the operating spectral range of an optoelectronic device through a dual-color active material integrated with a simple resonant waveguide structure. The TM waveguide mode and the SPP mode of the resonant waveguide structure are regulated to match the two active regions of the dual-color material both spectrally and spatially. Applying this scheme to a long-wavelength infrared quantum well photodetector, the absorption efficiencies at the two peak detection wavelengths of the dual-color quantum wells are both enhanced by more than 10 times compared with the case of a standard 45° edge facet coupled device with the same detection material. The simple light coupling structure is easy to accomplish and compatible with focal plane arrays. For thermal radiation detection, the absorption efficiency of the 300 K blackbody radiation by our dual-color detector is 83.8% higher than that by a single-color detector with the optimized structural parameters. Moreover, either polarization sensitive or polarization insensitive detection could be achieved in this dual-color infrared quantum well photodetector by using anisotropic or isotropic gratings.

On the Near-Pole Hole Insertion Layer and the Far-Pole Hole Insertion Layer for Multi-Quantum-Well Deep Ultraviolet Light-Emitting Diodes.

A novel Multi-Quantum-Well Deep Ultra Violet Light Emitting Diode (DUV-LED) device with a near-pole hole insertion layer and far-pole hole insertion layer was proposed and carefully studied. It was found that remarkable enhancements both in the light output power (LOP) and the internal quantum efficiency (IQE) could be realized by using the far-electrode hole insertion layer and near-electrode hole insertion layer compared to the conventional DUV-LED device. Inserting the near-polar hole insertion layer can increase the electric field in the hole injection layer, which will promote the ionization of the acceptor, increase the hole concentration, and enhance the light-emitting performance of the device. In addition, inserting the far-pole hole insertion layer can suppress electron leakage and promote the hole injection. At the same time, the updated electron barrier height of P-AlGaN/GaN will indirectly weaken the electrostatic field in the hole injection layer, which remains inconducive to the ionization of the acceptor, implying that the electrostatic field between the P-AGaN/GaN layer can optimize the efficiency droop of the device.

Plasma Engineering of Basal Sulfur Sites on MoS2 @Ni3 S2 Nanorods for the Alkaline Hydrogen Evolution Reaction.

Inexpensive and efficient catalysts are crucial to industrial adoption of the electrochemical hydrogen evolution reaction (HER) to produce hydrogen. Although two-dimensional (2D) MoS2 materials have large specific surface areas, the catalytic efficiency is normally low. In this work, Ag and other dopants are plasma-implanted into MoS2 to tailor the surface and interface to enhance the HER activity. The HER activty increases initially and then decreases with increasing dopant concentrations and implantation of Ag is observed to produce better results than Ti, Zr, Cr, N, and C. At a current density of 400 mA cm-2 , the overpotential of Ag500-MoS2 @Ni3 S2 /NF is 150 mV and the Tafel slope is 41.7 mV dec-1 . First-principles calculation and experimental results reveal that Ag has higher hydrogen adsorption activity than the other dopants and the recovered S sites on the basal plane caused by plasma doping facilitate water splitting. In the two-electrode overall water splitting system with Ag500-MoS2 @Ni3 S2 /NF, a small cell voltage of 1.47 V yields 10 mA cm-2 and very little degradation is observed after operation for 70 hours. The results reveal a flexible and controllable strategy to optimize the surface and interface of MoS2 boding well for hydrogen production by commercial water splitting.

Stacked Dual-Band Quantum Well Infrared Photodetector Based on Double-Layer Gold Disk Enhanced Local Light Field.

We propose a stacked dual-band quantum well infrared photodetector (QWIP) integrated with a double-layer gold disk. Two 10-period quantum wells (QW) operating at different wavelengths are stacked together, and gold nano-disks are integrated on their respective surfaces. Numerical calculations by finite difference time domain (FDTD) showed that the best enhancement can be achieved at 13.2 and 11.0 µm. By integrating two metal disks, two plasmon microcavity structures can be formed with the substrate to excite localized surface plasmons (LSP) so that the vertically incident infrared light can be converted into electric field components perpendicular to the growth direction of the quantum well (EZ). The EZ electric field component can be enhanced up to 20 times compared to the incident light, and it is four times that of the traditional two-dimensional hole array (2DHA) grating. We calculated the enhancement factor and coupling efficiency of the device in the active region of the quantum well. The enhancement factor of the active region of the quantum well on the top layer remains above 25 at the wavelength of 13.2 µm, and the enhancement factor can reach a maximum of 45. Under this condition, the coupling efficiency of the device reaches 2800%. At the wavelength of 11.0 µm, the enhancement factor of the active region of the quantum well at the bottom is maintained above 6, and the maximum can reach about 16, and the coupling efficiency of the device reaches 800%. We also optimized the structural parameters and explored the influence of structural changes on the coupling efficiency. When the radius (r1, r2) of the two metal disks increases, the maximum coupling efficiency will be red-shifted as the wavelength increases. The double-layer gold disk structure we designed greatly enhances the infrared coupling of the two quantum well layers working at different wavelengths in the dual-band quantum well infrared photodetector. The structure we designed can be used in stacked dual-band quantum well infrared photodetectors, and the active regions of quantum wells working at two wavelengths can enhance the photoelectric coupling, and the enhancement effect is significant. Compared with the traditional optical coupling structure, the structure we proposed is simpler in process and has a more significant enhancement effect, which can meet the requirements of working in complex environments such as firefighting, night vision, and medical treatment.

Ni3S2 Nanocomposite Structures Doped with Zn and Co as Long-Lifetime, High-Energy-Density, and Binder-Free Cathodes in Flexible Aqueous Nickel-Zinc Batteries.

Flexible rechargeable Zn//Ni batteries are attractive owing to their high energy density, good safety, inexpensive cost, and simple manufacturing process. However, the effects of metal doping on the properties of Ni3S2 cathodes in Zn/Ni batteries are not well understood. Herein, a binder-free Ni3S2 electrode is doped with Zn and Co and the nanocomposite structures are prepared on nickel foam (named ZCNS/NF) by a simple two-step hydrothermal technique. The ZCNS/NF//Zn battery delivers excellent electrochemical performance such as a working voltage window can be as high as 2.05 V, a capacity of 2.3 mAh cm-2 at 12 mA cm-2, and 82% retention going through 2000 cycles at 20 mA cm-2. The battery has a maximum output area energy density of 1.8 mWh cm-2 (462 Wh kg-1) and a power density of 36.8 mW cm-2 (9.2 kW kg-1). In addition, the flexible battery remains operational while being bent at a large angle and even punctured. The high performance and robustness of the composite cathode suggest that the design principle and materials have large commercial potential in Ni//Zn batteries.

Manganese molybdate nanoflakes on silicon microchannel plates as novel nano energetic material.

Nano energetic materials have attracted great attention recently owing to their potential applications for both civilian and military purposes. By introducing silicon microchannel plates (Si-MCPs) three-dimensional (3D)-ordered structures, monocrystalline MnMoO4 with a size of tens of micrometres and polycrystalline MnMoO4 nanoflakes are produced on the surface and sidewall of nickel-coated Si-MCP, respectively. The MnMoO4 crystals ripen controllably forming polycrystalline nanoflakes with lattice fringes of 0.542 nm corresponding to the [Formula: see text] plane on the sidewall. And these MnMoO4 nanoflakes show apparent thermite performance which is rarely reported and represents MnMoO4 becoming a new category of energetic materials after nanocrystallization. Additionally, the nanocrystallization mechanism is interpreted by ionic diffusion caused by 3D structure. The results indicate that the Si-MCP is a promising substrate for nanocrystallization of energetic materials such as MnMoO4.

The device performance of Cu(In, Ga)Se2 solar cells influenced by the type-inverted layer.

The type-inversion to n-type at the surface of p-type Culn(1-x)Ga(x)Se2 absorber layer is taken as an important factor for the high efficiency of Culn(1-x)Ga(x)Se2 (CIGS) with low Ga content, however, the further increase of Ga content makes the n-type doping difficult and the type-inverted layer vanish, which may have a negative effect on the device performance. Previous first-principles calculation had shown that the donor density becomes lower and level deeper when Ga content increases, while it's not clear how significantly the changes in the type-inverted layer influence the device performance. Through device simulation, we show that the efficiency decreases obviously as the donor density becomes lower and the level deeper in the inversion layer, thus they are important factors responsible for the limitation of the efficiency of CIGS solar cell, i.e., the efficiency decreases as Ga content exceeds 30%. Our work gives a good example in how to combine the electronic structure calculation of materials and device simulation to explain the experimental observation.

A comprehensive model of electrical noise in AlGaAs/GaAs long-wavelength quantum well infrared photodetectors.

We present the results of a comprehensive model for the electric noise simulation of a kind of nano-optoelectronics device: AIGaAs/GaAs long-wavelength quantum well infrared photodetectors (LW-QWIPs) in dark conditions by assuming a three-dimensional carrier transport in the barriers where the electrical field are obtained in a self-consistent way. This model takes into account all the fundamental mechanisms involved in the device detection process. The electrical field distribution, dark currents, electrical noise are carefully calculated and analyzed. The numerical results also explain well our experimental observations.