Nitride-based ultraviolet Schottky barrier photodetectors with LT-AlN cap layers

We present the characteristics of novel GaN-based ultraviolet (UV) Schottky barrier photodetectors (PDs) with a low-temperature (LT-)AlN cap layer. Comparing them with conventional Schottky barrier PDs, it was found that we achieved smaller dark current and larger UV to visible rejection ratio from the PDs with the LT-AlN cap layer. The dark leakage current for the Schottky barrier PDs with the LT-AlN cap layer was shown to be about four orders of magnitude smaller than that for the conventional Schottky barrier PDs. With −5 V applied bias, the measured responsivity and UV to visible rejection ratio are 0.16 A /W and 7.74×10² for the Schottky barrier PDs with the LT-AlN cap layer, respectively. This result can be attributed to the thicker and higher potential barrier when the LT-AlN cap layer was inserted.     

Metamaterials: from microwaves to the visible region

In a recent paper, J.B. Pendry [J.B. Pendry, Negative refraction makes a perfect lens, Phys. Rev. Lett. 86 (2000) 3966–3969] has mentioned the possibility of making perfect lenses using a slab of left-handed material with relative permeability and permittivity equal to −1. He gave a demonstration of the vital influence of the evanescent waves in this process, arguing that these waves are amplified inside the slab. In the present paper, we first try to give a rigorous electromagnetic demonstration of Pendry's statement, and we show that in fact the integral expression of the field in a region of space diverges. Since this divergence does not prove that the perfect lens does not exist, we then give a very simple theoretical demonstration that a homogeneous material with both relative permittivity and permeability equal to −1 cannot exist, even for a unique frequency. However, thanks to the heterogeneous nature of a metamaterial, it is shown that a material able to focus light more efficiently than current devices (but not perfectly) could exist. Finally, it is shown that a plane slab of dielectric photonic crystal can also focus light, a property which could be crucial for construction of superlenses in the visible and infrared regions. To cite this article: D. Maystre et al., C. R. Physique 6 (2005).     

Deep-ultraviolet and visible dual-band photodetectors by integrating Chlorin e6 with Ga_2O_3

Gallium oxide(Ga_2O_3) is a promising material for deep-ultraviolet(DUV) detection. In this work, Chlorin e6(Ce6)has been integrated with Ga_2O_3 to achieve a DUV and visible dual-band photodetector, which can achieve multiple target information and improve the recognition rate. The photodetector shows two separate response bands at 268 nm and 456 nm.The DUV response band has a responsivity of 9.63 A/W with a full width at half maximum(FWHM) of 54.5 nm; the visible response band has a responsivity of 1.17 A/W with an FWHM of 45.3 nm. This work may provide a simple way to design and fabricate photodetectors with dual-band response.     

NIR to visible upconversion emission from Dy: ZBLYAN glasses

This paper reports on the near infrared (730-783 nm) to the visible upconversion emissions at 482 nm (⁴F_9/2→⁶H_15/2), 576 nm (⁴F_9/2→⁶H_13/2) and 662 nm (⁴F_9/2→⁶H_11/2) from the Dy³⁺doped 53ZrF₄-20BaF₂-2LaF₃-2YF₃-3AlF₃-19NaF-1DyF₃ glasses. We have also carried out a systematic study on the normal emission properties of these glasses in order to understand their performance both as a NIR upconverted visible luminescent and as normal visible fluorescent optical systems of technical importance. With an increase in Dy³⁺ concentration beyond a particular value (1 mol%), activator-activator interaction becomes a significant cause of concentration quenching in the luminescence properties. The dependence of the emission spectra on the excitation wavelengths has also been examined and 451 nm was found to be the ideal excitation wavelength in the measurement of normal fluorescence spectra. In the case of NIR upconverted visible emission, we have observed that the NIR excitation at 783 nm as the suitable pump wavelength in demonstrating prominent visible emission colours from these glasses. The relevance in undertaking these optical materials lies in their potential for upconversion laser application in the visible wavelength region. The NIR upconversion phenomenon has been explained in terms of energy level schemes due to excited state absorption (ESA) and energy transfer upconversion (ETU) processes.     

Photoacoustic signal enhancement at visible and X-ray wavelengths

Good agreement between theory and experiment is found for photoacoustic (PA) signal enhancement by volatile liquids adsorbed on solid samples in a microphonic cell illuminated with visible light. When the same solid samples are illuminated with synchrotron X-radiation significantly smaller PA signal enhancements are observed than are predicted by theory because of radiolysis of the liquid vapors. The introduction of the volatile liquids is nevertheless valuable for the X-ray photoacoustic measurements because it raises the signal above the threshold for detectability.     

X-ray generation induced by visible lasers in ZnS aqueous suspensions

We present experimental results on the interaction of pulsed laser radiation with ZnS-quantum-dot aqueous suspensions. We detect luminescence in the blue spectral range as well as narrow beams of X-ray radiation. We describe the experimental conditions of X-ray generation and discuss the triboluminescence as a possible mechanism of the emission.     

X-ray, visible and electron spectroscopy with the NIST EBIT

An overview is given of recent activities at the NIST electron beam ion trap (EBIT) facility. The machine has been operational for almost three years. Important characteristics and demonstrated capabilities of our EBIT are presented. Selected results include experiments with trapped highly charged ions (X-ray and visible spectroscopy), and with extracted ions (ion-surface collision studies). This revised version was published online in August 2006 with corrections to the Cover Date.     

Improved ultraviolet/visible rejection ratio using MgZnO/SiO2/n-Si heterojunction photodetectors

We report on the fabrication and characterization of MgZnO/SiO₂/n-Si structured photodetectors, for the visible-blind monitoring. The current-voltage curve of the heterojunction shows obvious rectifying behaviors. In the visible range, the photocurrent decreased rapidly. In additionally, the ultraviolet/visible rejection ratio (R340 nm/R500 nm) was about four orders of magnitude at reverse bias, indicating a high degree of visible blindness. The key role of the insulating SiO₂ layer will be discussed in terms of the band diagrams of the heterojunctions.     

The way to high-performance single nanowire photodetectors: problems and prospects

<正>As potential building blocks for micro-nano devices,one-dimensional semiconductor nanowires(NWs)have been widely studied in recent decades.Due to limited dimension and large surface-to-volume ratio,devices based on NWs are more likely to exhibit unique properties.NW photodetectors adopting different materials have been fabricated.However,the performance is greatly affected by several issues such as lattice quality,surface homogeneity,contact electrodes and     

可见光到远红外波段气溶胶衰减计算模式

 建立了一种根据实测的气溶胶尺度谱分布(Junge指数)、地面能见度、相对湿度和气溶胶衰减廓线计算空间任意两点的气溶胶衰减计算模式,光谱波段范围覆盖了从可见光到远红外(1~25 000 cm^-1)。利用该气溶胶模式及国际上流行软件MODTRAN中的气溶胶模式同时和光栅太阳辐射计(pgs100)实测气溶胶衰减进行了对比,这种模式与MODTRAN相比,因考虑了气溶胶的实际尺度谱分布和高度分布,计算结果更接近实测值。利用所建立的气溶胶模式还分析了气溶胶衰减受各参数的影响,结果表明：气溶胶衰减受各参数影响较大,说明实测气溶胶参数在计算气溶胶衰减中起重要作用。将此气溶胶模式嵌入到我们自己研制的通用大气辐射传输软件CART中进行大气透过率和大气辐射传输的计算,有助于提高计算精度和增强功能。     

可见光到远红外波段气溶胶衰减计算模式

建立了一种根据实测的气溶胶尺度谱分布(Junge指数)、地面能见度、相对湿度和气溶胶衰减廓线计算空间任意两点的气溶胶衰减计算模式,光谱波段范围覆盖了从可见光到远红外(1~25 000 cm-1)。利用该气溶胶模式及国际上流行软件MODTRAN中的气溶胶模式同时和光栅太阳辐射计(pgs100)实测气溶胶衰减进行了对比,这种模式与MODTRAN相比,因考虑了气溶胶的实际尺度谱分布和高度分布,计算结果更接近实测值。利用所建立的气溶胶模式还分析了气溶胶衰减受各参数的影响,结果表明：气溶胶衰减受各参数影响较大,说明实测气溶胶参数在计算气溶胶衰减中起重要作用。将此气溶胶模式嵌入到我们自己研制的通用大气辐射传输软件CART中进行大气透过率和大气辐射传输的计算,有助于提高计算精度和增强功能。     

An FDTD approach to the simulation of quantum-well infrared photodetectors

A Finite Difference Time Domain approach is used to design and to optimize quantum-well based infrared photodetectors. Results showing the influence of some parameters on the performance of these devices are presented and discussed.     

Spin-resolved NEXAFS from resonant X-ray scattering (RXS): Application to MnO

Resonantly excited metal K core line spectra of NiO, MnO, CuO and other compounds have been investigated at the beamlines X21 (NSLS/BNL), BW1 and W1.1 (HASYLAB/DESY). A novel technique for quantitative resolution of NEXAFS spectra into spin-up and spin-down components has been developed. Since the method employs spin conservation and local spin references, it needs no circularly polarized radiation and no sample magnetization for taking both the RXS and NEXAFS spectra. Hence antiferromagnetic and paramagnetic materials can be investigated as well.By utilizing linear dichroism with angular-dependent measurements on single-crystal samples, additional resolution of NEXAFS spectra is possible with respect to the orbital symmetry. Application of the method to paramagnetic MnO, for the first time, provides new and unambiguous experimental results confirming modern (LSDA+U) calculations. Received: 29 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Manipulate light polarizations with metamaterials: From microwave to visible

Polarization is an important characteristic of electromagnetic (EM) waves, and efficient manipulations over EM wave polarizations are always desirable in practical applications. Here, we review the recent efforts in controlling light polarizations with metamaterials, at frequencies ranged from microwave to visible. We first presented a 4 × 4 version transfer matrix method (TMM) to study the scatterings by an anisotropic metamaterial of EM waves with arbitrary propagating directions and polarizations. With the 4 × 4 TMM, we discovered several amazing polarization manipulation phenomena based on the reflection geometry and proposed corresponding model metamaterial systems to realize such effects. Metamaterial samples were fabricated with the help of finite-difference-time-domain (FDTD) simulations, and experiments were performed to successfully realize these ideas at both microwave and visible frequencies. Efforts in employing metamaterials to manipulate light polarizations based on the transmission geometry are also reviewed.     

Intense visible luminescence from Nd-doped yttrium oxysulfide

We report on a novel luminescent phenomenon in Y₂O₂S doped with Nd³⁺. After irradiation by a 261 nm ultraviolet (UV) light into the Y₂O₂S host lattice, the Nd³⁺-doped Y₂O₂S phosphor emits intense blue luminescence in the visible light region. Moreover, this blue luminescence can also be obtained by exciting directly into the Nd³⁺ energy absorption itself. XRD, photoluminescence, and fluorescence decay curve are used to characterize the synthesized phosphor. The spectroscopic data indicate that all the visible emission peaks are originated from the electrical transitions of Nd³⁺, and the strong luminescence of the Nd³⁺ is considered to be due to an efficient energy transfer from the Y₂O₂S host lattice to the Nd³⁺ in Y₂O₂S:Nd³⁺. The optimum concentration for the luminescence Nd³⁺ is determined to be 1 mol% of Y³⁺ in Y₂O₂S host. The critical energy transfer distance has been calculated by the concentration quenching and the possible luminescent process of this blue luminescence-emitting phosphor is also investigated.     

超小碳纳米管的高效率光致可见发光

镶嵌在分子筛骨架中的4A直径的单壁碳纳米管可发出高效的、位于可见光区的光致发光．发光谱呈较宽的线形，其效率约为1％—5％．无论是对激发光的响应，还是发光强度都有很强的偏振依赖特性．结合其吸收光谱、拉曼光谱以及电子能带结构的理论计算，作者讨论了4A碳纳米管的发光机制，并给出了合理的解释．     

Metal halide perovskite photodetectors: Material features and device engineering

In recent years, the rapid progress of metal halide perovskite solar cells has been witnessed by the rocketing power conversion efficiency. In addition, perovskites have opened up a great opportunity for high performance photodetectors(PDs), due to their attractive optical and electrical properties. This review summarizes the latest progress of perovskitebased PDs, aiming to give a comprehensive understanding of the material design and device engineering in perovskite PDs.To begin with, the performance parameters and device configurations of perovskite PDs are introduced, which are the basis for the next discussion. Next, various PDs based on perovskites in different morphologies are discussed from two aspects:the preparation method, and device performance. Then, several device engineering strategies to enhance the performance of perovskite-based PDs are highlighted, followed by the introduction of flexible and narrow-band perovskite PDs. Finally,key issues and major challenges of perovskite PDs that need to be addressed in the future are outlined.     

Absolute calibration of photodetectors: photocurrent multiplication versus photocurrent subtraction

We report testing of the new absolute method of photodetector calibration based on the difference-signal measurement for two-mode squeezed vacuum by comparison with the traditional absolute method based on coincidence counting. Using low-gain parametric downconversion, we have measured the quantum efficiency of a counting detector by both methods. The difference-signal method was adapted for the counting detectors by taking into account the dead-time effect.