Numerical Modeling of Silicon Photodiodes for High-Accuracy Applications Part II. Interpreting Oxide-Bias Experiments

The semiconductor device modeling program PC-1D and the programs that support its use in high-accuracy modeling of photodiodes, all of which were described in Part I of this series of papers, are used to simulate oxide-bias self-calibration experiments on three different types of silicon photodiodes. It is shown that these simulations can be used to determine photodiode characteristics, including the internal quantum efficiency for the different types of photodiodes. In the latter case, the simulations provide more accurate values than can be determined by using the conventional data reduction procedure, and an uncertainty estimate can be derived. Finally, it is shown that 0.9997 ± 0.0003 is a nominal value for the internal quantum efficiency of one type of photodiode over the 440 to 460 nm spectral region.     

Interpolation of the spectral responsivity of silicon photodetectors in the near ultraviolet

We improve the methods used to interpolate the responsivity of unbiased silicon photodetectors in the near-ultraviolet region. This improvement is achieved by the derivation of an interpolation function for the quantum yield of silicon and by consideration of this function in the interpolation of the internal quantum efficiency of photodiodes. The calculated quantum-yield and spectral-responsivity values are compared with measurement results obtained by the study of a silicon trap detector and with values reported by other research groups. The comparisons show agreement with a standard deviation of 0.4% between our measured and modeled values for both the quantum yield and the spectral responsivity within the wavelength region from 260 to 400 nm. The proposed methods thus extend the predictability of the spectral responsivity of silicon photodetectors to the wavelength region from 260 to 950 nm. Furthermore, an explanation is proposed for the change in the spectral responsivity of silicon photodiodes that is due to UV radiation. In our improved quantum efficiency model the spectral change can be accounted for completely by the adjustment of just one parameter, i.e., the collection efficiency near the SiO(2)/Si interface.     

Quantum efficiency of silicon photodiodes in the near-infrared spectral range

The quantum efficiency of silicon photodiodes and factors that might be responsible for the drop in quantum efficiency in the near-infrared spectral range were analyzed. It was shown that poor reflectivity from the rear surface of the die could account for a decrease in Si photodiode quantum efficiency in near-infrared spectral range by more than 20%. The photodiode quantum efficiency was modeled with an appropriate representation for the carrier-collection efficiency dependence on the die penetration depth. A corrected analytical expression for calculating the photodiode quantum efficiency is given. Some methods to improve the quantum efficiency of silicon photodiodes in near-infrared spectral range are discussed.     

Irradiation stability of silicon photodiodes for extreme-ultraviolet radiation

Photodiodes are used as easy-to-operate detectors in the extreme-ultraviolet spectral range. At the Physikalisch-Technische Bundesanstalt photodiodes are calibrated with an uncertainty of spectral responsivity of 0.3% or less. Stable photodiodes are a prerequisite for the dissemination of these high-accuracy calibrations to customers. Silicon photodiodes with different top layers were exposed to intense extreme-ultraviolet irradiation. Diodes coated with diamondlike carbon or TiSiN proved to be stable within a few percent up to a radiant exposure of 100 kJ/cm2. The changes in responsivity could be explained as being due to carbon contamination and to changes in the internal charge collection efficiency. In ultrahigh vacuum, no indication of oxidation was found.     

3D打印发展背景下三维建模软件变革趋势分析

目的作为3D打印重要的辅助工具,现有三维建模软件针对专业用户开发设计,并不适用于普通用户。分析三维建模软件的变革趋势,目的在于让普通用户更方便地使用3D打印设备。方法采用实例分析方法,对具有代表性的三维建模软件进行分析。结论提出面向普通用户的三维建模软件开发思路,包括操作界面图形符号化、信息架构扁平化、建模功能智能化以及基于浏览器的三维建模软件服务平台。     

Laser-textured silicon photodiode with broadband spectral response

A femtosecond-laser-textured Si photodetector is reported. Broadband spectral optical response is detected from UV to NIR. A quantum efficiency of greater than 80% from 490 nm to 780 nm has been achieved. The quantum efficiency at 245 nm is 62%, which is comparable to UV-enhanced Si photodiodes. The bandwidth of a 250-μm-diameter device is 60 MHz.     

基于SPM的超媒体人机接口

当利用扫描隧道显微镜(SPM)作为一种纳米操作工具时,由于其缺乏实时的传感器信息反馈,而大大阻碍了它的广泛应用．利用超媒体人机交互接口可以解决这个问题．在纳米操作过程中,超媒体接口不但可以为操作者提供可实时更新的仿真操作场景,还可以通过力反馈手柄让操作者实时地感受到探针受到的三维纳米操作力．除此之外,操作者还可以通过该手柄直接控制探针的三维运动．最后在聚碳酸酯上进行了超媒体人机接口的纳米刻画实验．实验结果验证了该系统的有效性和效率．     

Photon counting with passively quenched germanium avalanche

We demonstrate photon counting in germanium avalanche photodiodes biased beyond breakdown and quenched with a simple series resistance circuit. The devices show moderate (> 7%) quantum efficiency with limited afterpulsing and dark counts and subnanosecond jitter.     

Characteristics of III-nitride photodiodes with self-assembled quantum dots

In this work, it has been demonstrated that metal–semiconductor–metal (MSM) photodiodes (PDs) with InGaN self-assembled quantum dots (QDs) were fabricated and compared with conventional InGaN MSM photodiodes. The scanning near-field optical microscope (SNOM) results revealed that such InGaN nanostructures could have better absorption for the near-field light with the wavelength of 457–514 nm. It was found that the InGaN QD photodiode with lower dark current can operate in the normal incidence mode; we could achieve a much larger photocurrent to dark current contrast ratio from MSM photodiodes with nanoscale InGaN quantum dots. It was also found that the measured responsivity of MSM photodiodes with QDs and without QDs approximated to the same in the range of 390–460 nm. Furthermore, the photodiodes with QDs showed higher spectral response than that of the photodiodes without QDs at wavelengths < 350 nm and > 480 nm.     

基于用户体验的云建模平台界面设计研究

目的 从用户体验视角出发,探究运用于云建模平台的界面设计策略。方法 通过用户在使用云建模平台时的视觉感知体验、交互感知体验和心理感知体验三个维度,对比和分析两款云建模平台（Onshape、Fusion 360）的异同点与优缺点,提出基于用户体验的云建模平台界面设计策略,根据该策略对云图三维云建模平台的界面进行优化设计,最终以可用性测试检验该策略的有效性。结论 通过对两款云建模平台在视觉、交互、心理三个维度上的体验分析,得出以下四类设计策略：强化使用过程的专注度、提升界面使用的友好度、增强实时协作界面可视化和注重细节设计的精致化,运用上述四类设计策略指导设计实践可有效提高云建模平台的可用性与用户满意度,为云建模平台提供界面设计依据与新的设计导向。     

Ultrafast superconducting single-photon detectors for near-infrared-wavelength quantum communications

Abstract

The paper reports progress on the design and development of niobium-nitride, superconducting single-photon detectors (SSPDs) for ultrafast counting of near-infrared photons for secure quantum communications. The SSPDs operate in the quantum detection mode, based on photon-induced hotspot formation and subsequent appearance of a transient resistive barrier across an ultrathin and submicron-width superconducting stripe. The devices are fabricated from 3.5 nm thick NbN films and kept at cryogenic (liquid helium) temperatures inside a cryostat. The detector experimental quantum efficiency in the photon-counting mode reaches above 20% in the visible radiation range and up to 10% at the 1.3–1.55 μn infrared range. The dark counts are below 0.01 per second. The measured real-time counting rate is above 2 GHz and is limited by readout electronics (the intrinsic response time is below 30 ps). The SSPD jitter is below 18 ps, and the best-measured value of the noise-equivalent power (NEP) is 2 × 10^?18 W/Hz^1/2. at 1.3 μm. In terms of photon-counting efficiency and speed, these NbN SSPDs significantly outperform semiconductor avalanche photodiodes and photomultipliers.     

Stability of photodiodes under irradiation with a 157-nm pulsed excimer laser

We have measured the stability of a variety of photodiodes exposed to 157-nm light from a pulsed excimer laser by using a radiometry beamline at the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology. The intense, pulsed laser light exposed the photodiodes, whereas the low-intensity, continuously tunable light from the synchrotron source measured changes in the characteristics of the photodiodes, such as in the responsivity and the reflectance from the surface of a photodiode. Photodiodes studied include both silicon pn-junction and Schottky-barrier types. Among these photodiodes, we found that the damage mechanism for photodiodes with SiO2-based passivating layers is mainly the buildup of SiO2-Si interface trap states. The interface trap state buildup is well known for other semiconductor devices and is generally recognized as a product induced by radiation with an energy more than the 9-eV SiO2 bandgap energy rather than the 7.9-eV energy of the 157-nm radiation. Based on the generation of interface trap states, a model is proposed to describe the dependence of detector responsivity on exposure to 157-nm radiation. We also observed slow recovery in some of the damaged photodiodes, confirming that some of the interface trap states are only semipermanent. Radiation damage induced by low-power continuous 157-nm synchrotron light was also studied. As for the other photodiodes with no SiO2 layers, measurement results support the assumption that the changes in responsivity are due mainly to the deposition of thin layers on the tops of the detectors during laser irradiation.     

Performance enhancement of GaN-based light-emitting diodes by surface plasmon coupling and scattering grating

Using the analysis of the evanescent surface plasmon polariton (SPP) mode at the GaN/Ag interface as basis, we propose a light-emitting diode (LED) structure with a plasmonic Ag nanostructure and sapphire grating to enhance external quantum efficiency. The 2D finite-difference time-domain method is used to study the spectral properties of the hybrid structure and the effects of structural parameters on light emission enhancement. The plasmonic Ag nanostructure couples recombination energy to the SPP modes at the GaN/Ag interface, whereas the sapphire grating scatters photons out of the LED chips with high extraction efficiency. Under optimal parameters, external quantum efficiency enhancement increases to approximately eighteen times the original value at a relatively long wavelength.     

Accurate fluid-structure interaction computations using elements without mid-side nodes

The paper proposes a new analysis method for fluid-structure problems, which has nodal consistency at the fluid-structure interface and its calculation efficiency and accuracy are high. The incompressible viscous fluid analysis method using the P1-P1 element based on SUPG/PSPG developed by Tezduyar et al. is used for fluid analysis, while the high-accuracy analysis method based on EFMM developed by the authors is adopted for structure analysis. As the common feature of these methods, it is possible to analyze a fluid or a structure rather accurately by using the first-order triangular or tetrahedral elements. In addition, variables are exchanged exactly at the common nodes on the fluid-structure boundary without deteriorating accuracy and calculation efficiency due to the interpolation of variables between nodes. The present method is applied to a fluid-structure interaction problem by simulating the deformation of a red blood cell.     

Temperature Dependent Characteristics of Nonreach-Through 4H-SiC Separate Absorption and Multiplication APDs for UV Detection

Silicon carbide (SiC) separate absorption multiplication region avalanche photodiodes (SAM-APDs) for UV detection in harsh environment applications were designed and fabricated. The devices were intentionally designed to operate under nonreach-through conditions in order to eliminate field-induced leakage current. The gain of 2500 and quantum efficiency of ~45% at room temperature were achieved at the wavelength of 290-300 nm for a packaged device with an active area of 1 x 1 mm². The temperature dependency of the current-voltage characteristics and responsivity was examined in the temperature range from room temperature to 230degC.     

Photodiodes based on InAs/InAsSb/InAsSbP heterostructures with quantum efficiency increased by changing directions of reflected light fluxes

It is shown, using the example of InAs/InAsSb/InAsSbP heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of a photodiode chip leads to an increase in the quantum efficiency of photodiodes by a factor of 1.5–1.7 in the entire mid-IR wave-length interval studied (λ = 3–5 μm). For the obtained photodiodes with a cutoff wavelength of 4.8 μm, a photosensitive area of 0.1 mm², and a chip area of 0.9 mm², a monochromatic responsivity at λ = 4.0 μm reached 0.6 A/W, while a dark current at a reverse bias voltage of 0.2 V was within 4–6 A/cm².     

基于真实世界隐喻的虚拟现实用户界面范式研究及应用

目的 基于真实世界隐喻,研究虚拟现实用户界面范式,并指导应用实践。方法 通过整理虚拟现实和用户界面的相关文献资料,以基于真实世界的交互（RBI框架）作为指导,引出真实世界隐喻4个方面的要素,对比WIMP范式各个基础元件所承载的作用,研究虚拟现实用户界面范式。结论 提出了虚拟现实用户界面SOMM范式,分析了SOMM范式每一个要素,描述了用户在虚拟现实中的三维交互过程,并应用于工业机器人VR岗位实训系统用户界面当中,验证了SOMM范式的可行性。SOMM范式能让用户在虚拟现实环境中执行自然人机交互,减少了用户认知转换负荷,为其他研究者和设计师提供了指导和思路。     

Theory of single-photon detectors employing smart strategies of detection

Single-photon detectors have become more important with the advent of set-ups for optical communication using single-photon pulses, mainly quantum key distribution. The performance of quantum key distribution systems depends strongly on the performance of single-photon detectors. In this paper, aiming to overcome the afterpulsing that limits strongly the maximal transmission rate of quantum key distribution systems, three smart strategies for single-photon detection are discussed using analytical and numerical procedures. The three strategies are: hold-off time conditioned to avalanche presence, termed the Norwegian strategy, using one avalanche photodiode, using two raffled avalanche photodiodes and using two switched avalanche photodiodes. Finally we give examples using these strategies in a quantum key distribution set-up.     

石墨烯纳米复合材料的降阶均匀化方法及其数值实现

对石墨烯纳米复合材料进行三维有限元建模通常需极其精细的网格。在考虑塑性演变的情况下,细观代表性单元体模型的计算效率极其低下。为此,基于非均匀变换场分析理论,提出了石墨烯纳米复合材料的降阶均匀化方法。首先,针对不同加载路径进行预分析,提取细观塑性应变场信息;然后对这些信息进行本征正交分解,从而得到若干个塑性模态,用作降阶模型的基函数;基于宏、细观耗散功的等效原理,导出降阶变量的本构模型。该方法的离线分析部分通过MATLAB编程实现。为了便于工程计算,在线分析部分则由商业有限元软件ABAQUS的UMAT用户子程序接口实现。基于三维算例分析,验证了所提方法的有效性。结果显示,在保证较高精度的前提下,针对三维代表性单元体计算的加速率可达103~104量级。      

Total absorption radiometers for precision measurement of low power levels

We investigate a self-calibrated, total absorption radiometer with 100% quantum efficiency in the visible region. The fundamental components of its residual systematic errors are presented: the limit of additive residual systematic noise does not exceed 0.06% at a wavelength of 632.8 nm. The radiometer is applied to high-accuracy spectrophotometric measurement of reflection and transmission coefficients. The standard deviation of these measurements is less than 0.01%.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 32–35, August, 1994.