Search

Optical superconducting transition-edge sensor (TES) has been widely used in quantum information, biological imaging, and fluorescence microscopy owing to its high quantum efficiency, low dark count, and photon number resolving capability. The temperature sensitivity (αI) and current sensitivity (βI) are important parameters for optical TESs, which are generally extracted from the complex impedance. Here we present a method to extract αI and βI based on a two-fluid model and compare the calculated current–voltage curves, pulse response, and theoretical energy resolution with the measured ones. This method shows qualitative agreement that is suitable for further optimization of optical TESs. [ABSTRACT FROM AUTHOR]

Graphene has excellent thirdorder nonlinear optical (NLO) properties due to its unique electronic band structure and wideband gap tunability. This paper focuses on the research progress of graphene and its composite materials in nonlinear optics in recent years. In this review, recent results on graphene (or graphene oxide)–metal nanoparticles (G-MNPs), graphene–metal–oxide nanoparticles (G-MONPs), graphene–metal sulfide nanoparticles (G-MSNPs), and graphene–organic molecular composites (G-OM) have been discussed. In addition, the enhancement mechanism of nonlinear absorption (NLA) and optical limiting (OL) have also been covered. [ABSTRACT FROM AUTHOR]

The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by firstprinciples calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0-13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO. [ABSTRACT FROM AUTHOR]

Torque measurements were performed on single crystal samples of Ca0.73La0.27(Fe0.96Co0.04)As2 in both the normal and superconducting states. Contributions to the torque signal from the paramagnetism and the vortex lattice were identified. The superconducting anisotropy parameter γ was determined from the reversible part of the vortex contribution based on Kogan's model. It is found that γ ≃ 7.5 at t = T/Tc = 0.85, which is smaller than the result of CaFe0.88Co0.12AsF γ ≃ 15 at t = 0.83, but larger than the result of 11 and 122 families, where γ stays in the range of 2–3. The moderate anisotropy of this 112 iron-based superconductor fills the gap between 11, 122 families and 1111 families. In addition, we found that the γ shows a temperature dependent behavior, i.e., decreasing with increasing temperature. The fact that γ is not a constant point towards a multiband scenario in this compound. [ABSTRACT FROM AUTHOR]

In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Al-doped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the n+-InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H2O as an oxidizer at temperatures as low as 400 °C without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510−4 Ω·cm), and an epitaxial-like excellent interface on p-GaN with an n+-InGaN contact layer. A forward voltage of 2.82 V @ 20 mA was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-III), and by 28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O2 as an oxidizer (LED-II), respectively. The results indicate that the AZO-TCL grown by MOCVD using H2O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application. [ABSTRACT FROM AUTHOR]

In this paper the single-event responses of the silicon germanium heterojunction bipolar transistors (SiGe HBTs) are investigated by TCAD simulations and laser microbeam experiment. A three-dimensional (3D) simulation model is established, the single event effect (SEE) simulation is further carried out on the basis of SiGe HBT devices, and then, together with the laser microbeam test, the charge collection behaviors are analyzed, including the single event transient (SET) induced transient terminal currents, and the sensitive area of SEE charge collection. The simulations and experimental results are discussed in detail and it is demonstrated that the nature of the current transient is controlled by the behaviors of the collector–substrate (C/S) junction and charge collection by sensitive electrodes, thereby giving out the sensitive area and electrode of SiGe HBT in SEE. [ABSTRACT FROM AUTHOR]

A 4Ă—4 beta-phase gallium oxide (β -Ga2O3) deep-ultraviolet (DUV) rectangular 10-fingers interdigital metal-semiconductor-metal (MSM) photodetector array of high photo responsivity is introduced. The Ga2O3 thin film is prepared through the metalorganic chemical vapor deposition technique, then used to construct the photodetector array via photolithography, lift-off, and ion beam sputtering methods. The one photodetector cell shows dark current of 1.94 pA, photo-to-dark current ratio of 6Ă—107, photo responsivity of 634.15 Aâ‹...Wâˆ'1, specific detectivity of 5.93Ă—1011 cmâ‹...Hz1/2â‹...Wâˆ'1 (Jones), external quantum efficiency of 310000%, and linear dynamic region of 108.94 dB, indicating high performances for DUV photo detection. Furthermore, the 16-cell photodetector array displays uniform performances with decent deviation of 19.6% for photo responsivity. [ABSTRACT FROM AUTHOR]

The degradation mechanism of GaN-based near-ultraviolet (NUV, 320â€"400 nm) light emitting diodes (LEDs) with low-indium content under electrical stress is studied from the aspect of defects. A decrease in the optical power and an increase in the leakage current are observed after electrical stress. The defect behaviors are characterized using deep level transient spectroscopy (DLTS) measurement under different filling pulse widths. After stress, the concentration of defects with the energy level of 0.47â€"0.56 eV increases, accompanied by decrease in the concentration of 0.72â€"0.84 eV defects. Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra, the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation, which was previously passivated with hydrogen. This study reveals the evolution process of defects under electrical stress and their spatial location, laying a foundation for manufacture of GaN-based NUV LEDs with high reliability. [ABSTRACT FROM AUTHOR]

We experimentally report on the evolution from singly-dressed to doubly-dressed four-wave mixing (FWM) process by controlling the powers of the probe, the pump and the dressing fields respectively. The differences in the enhancement and the suppression of FWM signal between the two-level and cascade three-level atomic systems are observed and explained by the multi-dressed effect theoretically. Both the x direction and the y direction spatial splittings of the degenerate-FWM (DWFM) beams are obtained. We also investigate the switch between the enhancement and the suppression of the DWFM signals and between its spatial splittings in x direction and y direction. The spatial splittings in x direction and y direction can be controlled by the relative position and the intensity of the involved laser beams. Such a study can be useful for optimizing the efficiency of the FWM process and providing potential applications in spatial signal processing [ABSTRACT FROM AUTHOR]

Si-doped β-Ga2O3 films are fabricated through metal-organic chemical vapor deposition (MOCVD). Solar-blind ultraviolet (UV) photodetector (PD) based on the films is fabricated by standard photolithography, and the photodetection properties are investigated. The results show that the photocurrent increases to 11.2 mA under 200 μW⋅cm−2 254 nm illumination and ± 20 V bias, leading to photo-responsivity as high as 788 A⋅W−1. The Si-doped β-Ga2O3-based PD is promised to perform solar-blind photodetection with high performance. [ABSTRACT FROM AUTHOR]

We report the edge-defined-film-fed (EFG)-grown β-Ga2O3-based Schottky photodiodes. The device has a reverse leakage current of ∼nA and a rectified ratio of ∼104 at ± 5 V. In addition, the photodiode detector shows a dark current of 0.3 pA, a photo-responsivity (R) of 2.875 mA/W, a special detectivity (D*) of 1010 Jones, and an external quantum efficiency (EQE) of 1.4% at zero bias, illustrating a self-powered operation. This work may advance the development of the Ga2O3-based Schottky diode solar-blind photodetectors. [ABSTRACT FROM AUTHOR]

Single event effects (SEEs) in a 28-nm system-on-chip (SoC) were assessed using heavy ion irradiations, and susceptibilities in different processor configurations with data accessing patterns were investigated. The patterns included the sole processor (SP) and asymmetric multiprocessing (AMP) patterns with static and dynamic data accessing. Single event upset (SEU) cross sections in static accessing can be more than twice as high as those of the dynamic accessing, and processor configuration pattern is not a critical factor for the SEU cross sections. Cross section interval of upset events was evaluated and the soft error rates in aerospace environment were predicted for the SoC. The tests also indicated that ultra-high linear energy transfer (LET) particle can cause exception currents in the 28-nm SoC, and some even are lower than the normal case. [ABSTRACT FROM AUTHOR]

This paper reports on a comparative study of the spatial distributions of the electrical, optical, and structural properties in an AlGaN/GaN heterostructure. Edge dislocation density in the GaN template layer is shown to decrease in the regions of the wafer where the heterostructure sheet resistance increases and the GaN photoluminescence band-edge energy peak shifts to a high wavelength. This phenomenon is found to be attributed to the local compressive strain surrounding edge dislocation, which will generate a local piezoelectric polarization field in the GaN layer in the opposite direction to the piezoelectric polarization field in the AlGaN layer and thus help to increase the two-dimensional electron gas concentration. [ABSTRACT FROM AUTHOR]

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 1014cm[?]3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 1016cm[?]3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current-voltage (I-V) characteristic, but has no effect on the transconductance in the saturation area. [ABSTRACT FROM AUTHOR]

This paper reports that (Ga, Mn)N is prepared using implantation of 3at.% Mn Ions into undoped GaN. Structural characterization of the crystals was performed using x-ray diffraction(XRD). Detailed XRD measurements have revealed the characteristic of Mn-ion implanted GaN with a small contribution of other compounds. With Raman spectroscopy measurements, the spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 747, 733 and 566 cm-1 identified as E1(LO), A1(LO) and E2H, respectively. The Mn-doped GaN layers exhibit additional excitations at 182, 288, 650-725, 363, 506 cm-1 and the vicinity of E2H mode. The modes observed at 182, 288, 650-725 cm-1 are assigned to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation. Other new phonon modes are assigned to Mnx-Ny, Gax-Mny modes and the local vibrational mode of Mn atoms in the (Ga, Mn)N, which are in fair agreement with the standard theoretical results. [ABSTRACT FROM AUTHOR]

Digital holography can be applied to ultrafast detection when a femtosecond laser pulse is used. In this paper, the interference process of two femtosecond laser pulses is studied and the recording process of the femtosecond laser pulsed digital hologram is simulated. Holograms at different recording angles are generated by integrating the instantaneous interference field. By analyzing the distribution of the reconstructed phase error, the characteristics of femtosecond laser pulsed digital holography are discussed. [ABSTRACT FROM AUTHOR]

The finite dissolution model of silicon particles in the aluminum melt is built and calculated by the finite difference method, and the lower dissolution limit of silicon particles in the aluminum melt is proposed and verified by experiments, which could be the origin of microinhomogeneity in aluminum—silicon melts. When the effects of curvature and interface reaction on dissolution are not considered; the dissolution rate first decreases and later increases with time. When the effects of curvature and interface reaction on dissolution are considered, the dissolution rate first decreases and later increases when the interface reaction coefficient (k) is larger than 10−1, and the dissolution rate first decreases and later tends to be constant when k is smaller than 10−3. The dissolution is controlled by both diffusion and interface reaction when k is larger than 10−3, while the dissolution is controlled only by the interface reaction when k is smaller than 10−4. [ABSTRACT FROM AUTHOR]

The anisotropic strain of a nonpolar (1120) a-plane GaN epilayer on an r-plane (1102) sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief. [ABSTRACT FROM AUTHOR]