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We demonstrate that the optical absorption is enhanced in small molecule organic solar cells by using a trapezoid grating structure. The enhanced absorption is mainly attributed to both waveguide modes and surface plasmon modes, which is simulated by using finite-difference time-domain method. The simulated results show that the surface plasmon along the semitransparent metallic Ag anode is excited by introducing the periodical trapezoid gratings, which induce the increase of high intensity field in the donor layer. Meanwhile, the waveguide modes result in a high intensity field in acceptor layer. The increase of field improves the absorption of organic solar cells significantly, which is demonstrated by simulating the electrical properties. The simulated results also show that the short-circuit current is increased by 31% in an optimized device, which is supported by the experimental measurement. Experimental result shows that the power conversion efficiency of the grating sample is increased by 7.7%. [ABSTRACT FROM AUTHOR]

We investigate the sensitivity and figure of merit (FOM) of a localized surface plasmon (LSP) sensor with gold nanograting on the top of planar metallic film. The sensitivity of the localized surface plasmon sensor is 317 nm/RIU, and the FOM is predicted to be above 8, which is very high for a localized surface plasmon sensor. By employing the rigorous coupled-wave analysis (RCWA) method, we analyze the distribution of the magnetic field and find that the sensing property of our proposed system is attributed to the interactions between the localized surface plasmon around the gold nanostrips and the surface plasmon polarition on the surface of the gold planar metallic film. These findings are important for developing high FOM localized surface plasmon sensors. [ABSTRACT FROM AUTHOR]

A localized plasmon resonance sensor consisting of an asymmetric split-ring resonator array sustaining highly localized field energy with high refractive index sensitivity and good figure of merit is demonstrated and investigated. In the proposed 3-cut split-ring resonator structure with broken symmetry, a highly tunable transmission with a large modulation depth and a narrow resonance linewidth is obtained, which shows polarization-insensitive and angle-independent properties. Numerical calculation results show that a high sensitivity of up to 1006 nm/RIU and a figure of merit of 9.7 can be reached. This plasmonic index sensor is practically obtainable, and is expected to have potential applications for high-sensitivity convenient and efficient detection. [ABSTRACT FROM AUTHOR]

A high power GaSb-based laser diode with lasing wavelength at 2 μm was fabricated and optimized. With the optimized epitaxial laser structure, the internal loss and the threshold current density decreased and the internal quantum efficiency increased. For uncoated broad-area lasers, the threshold current density was as low as 144 A/cm2 (72 A/cm2 per quantum well), and the slope efficiency was 0.2 W/A. The internal loss was 11 cm−1 and the internal quantum efficiency was 27.1%. The maximum output power of 357 mW under continuous-wave operation at room temperature was achieved. The electrical and optical properties of the laser diode were improved. [ABSTRACT FROM AUTHOR]

The performance of type-II superlattice (T2SL) long-wavelength infrared devices is limited by crystalline quality of T2SLs. We optimize the process of growing molecular beam epitaxy deposition T2SL epi-layers on GaSb (100) to improve the material properties. Samples with identical structure but diverse In/Ga beam-equivalent pressure (BEP) ratio are studied by various methods, including high-resolution x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy. We find that appropriately increasing the In/Ga BEP ratio contributes to improving the quality of T2SLs, but too large In BEP will much more easily cause a local strain, which can lead to more InSb islands in the InSb interfaces. The InSb islands melt in the InSb interfaces caused by the change of chemical potential of In atoms may result in the “nail” defects covering the whole T2SLs, especially the interfaces of GaSb-on-InAs. When the In/Ga BEP ratio is about 1, the T2SL material possesses a lower full width at half maximum of +1 first-order satellite peak, much smoother surface and excellently larger area uniformity. [ABSTRACT FROM AUTHOR]

We fabricated an acousto-optic semiconductor hybrid device for strong optomechanical coupling of individual quantum emitters and a surface acoustic wave. Our device comprises of a surface acoustic wave chip made from highly piezoelectric LiNbO3 and a GaAs-based semiconductor membrane with an embedded layer of quantum dots. Employing multi-harmonic transducers, we generated sound waves on LiNbO3 over a wide range of radio frequencies. We monitored their coupling to and propagation across the semiconductor membrane, both in the electrical and optical domain. We demonstrate the enhanced optomechanical tuning of the embedded quantum dots with increasing frequencies. This effect was verified by finite element modelling of our device geometry and attributed to an increased localization of the acoustic field within the semiconductor membrane. For moderately high acoustic frequencies, our simulations predict strong optomechanical coupling, making our hybrid device ideally suited for applications in semiconductor based quantum acoustics. [ABSTRACT FROM AUTHOR]

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using compositionally graded GaAsxSb buffer layers. Optimization of GaAsxSb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of GaAsxSb layers are found to be 420°C and 0.5 μm, respectively. The smallest full width at half maximum value and the root mean square surface roughness of 0.67 nm over 2 × 2 μm2 area are achieved as a 250 nm GaSb film is grown under optimized conditions. [ABSTRACT FROM AUTHOR]

Type-II InAs/GaSb superlattices made of 13 InAs monolayers (MLs) and 7 GaSb MLs are grown on GaSb substrates by solid source molecular beam epitaxy. To obtain lattice-matched structures, thin InSb layers are inserted between InAs and GaSb layers. We complete a series of experiments to investigate the influence of the InSb deposition time, V/III beam-equivalent pressure ratio and interruption time between each layer, and then characterize the superlattice (SL) structures with high-resolution x-ray diffraction and atomic force microscopy. The optimized growth parameters are applied to grow the 100-period SL structure, resulting in the full-width half-maximum of 29.55 arcsec for the first SL satellite peak and zero lattice-mismatch between the zero-order SL peak and the GaSb substrate peak. [ABSTRACT FROM AUTHOR]