The influence of a hydride preflow on the crystalline quality of InP grown on exactly oriented (100)Si

Several microns thick epitaxial InP films have been successfully deposited on exactly oriented (100) Si substrates by metal-organic vapour-phase epitaxy. We have studied the influence of a hydride preflow before buffer growth on the crystalline quality of the InP by measuring the surface roughness, by X-ray diffractometry, TEM and SEM investigations, and by detection of anti-phase-domains. Generally, an AsH₃ preflow instead of PH₃ improved the crystalline perfection considerably. Furthermore, if AsH₃ is introduced only during cool-down between 700 and 900° C after the thermal cleaning step anti-phase-domain free InP is grown.     

基于图像处理的螺丝钉计数方法研究

针对传统仓库管理系统中螺丝钉统计计数难题,将数字图像处理引入到螺丝钉检测计数中。提出了一种基于图像处理的螺丝钉自动计数方法。首先对未放置螺丝钉的货架进行处理,检测并记录放置螺丝钉的位置等信息,建立模板。在建立模板的过程中,采用人机交互的方式进行校正,能够有效地解决光照、噪声等带来的影响,从而建立准确的模板。然后将未放置螺丝钉的图像（模板图）与待检测图像相减,突出放置螺丝钉后的位置的特征。最后采用模板匹配法,检测对应位置是否存在螺丝钉。实验表明：该方法能够有效地解决货架受损、螺丝钉氧化和噪声干扰等情况带来的影响,并且实现简单。计数准确率高达98%以上,平均检测时间为3.67 ms,很大程度地提升了仓库管理性能。     

Low pressure MOVPE of InP from trimethylindium and phosphine

Epitaxial layers of InP have been grown by MOVPE at reduced chamber pressures from trimethylindium (TMI) and phosphine (PH₃) in a horizontal reactor. Growth rates and deposition efficiency show an increase of about 2 times as the pressure is reduced from 760 Torr (1 atm) to 9 Torr. Background impurities decrease to a minimum at 38 Torr (0.05 atm) for growth at 650° C. At 38 Torr the growth rates are linear with TMI flow above a threshold minimum and correlate to the carrier gas thermal conductivity in mixtures of H₂ + N₂. Uniformity of the layer thicknesses is influenced by pressure, temperature, gas flow rate and position of the substrate on the susceptor.     

一种钢筋图像自动计数的方法

针对常规基于图像处理的钢筋自动计数解决方案的不足,提出了一种简单可靠的解决方案。该解决方案的特点在于使用高斯模糊将粘连的钢筋图像转换成一个个驼峰型的光球,然后配合峰值提取准确地统计图像中的钢筋根数。实验证明,该方法对多根粘连钢筋的计数十分有效,大大提高了钢筋自动计数的准确率。     

Ensuring the reliability of alpha counting

Measuring the alpha flux at the surface of materials from integrated circuits and their packages has been established as a method for more than 2 decades. Largearea low-background counting systems from two vendors were used; these systems operate as proportional counters.^1,2 The results gained from these measurements were used to categorize possible causes of counting errors into groups. Some of these causes are focused on in more detail by the use of examples. It is demonstrated how the cumulative density function (CDF) of a distribution of measured counting rates can be tested graphically for Poisson distribution using two methods. A systematic error is demonstrated and the influence of the duration of the measurements on the detection limit is explained. It is also shown how a suitable bias point can be found for counting tubes. Finally, a schematic of results from alpha counting is presented, and time-dependent changes of these counting rates are stated.     

Modeling the photon counting and photoelectron counting characteristics of quanta image sensors

A signal chain model of single-bit and multi-bit quanta image sensors(QISs)is established.Based on the proposed model,the photoresponse characteristics and signal error rates of QISs are investigated,and the effects of bit depth,quantum efficiency,dark current,and read noise on them are analyzed.When the signal error rates towards photons and photoelec-trons counting are lower than 0.01,the high accuracy photon and photoelectron counting exposure ranges are determined.Fur-thermore,an optimization method of integration time to ensure that the QIS works in these high accuracy exposure ranges is presented.The trade-offs between pixel area,the mean value of incident photons,and integration time under different illumin-ance level are analyzed.For the 3-bit QIS with 0.16 e-/s dark current and 0.21 e-r.m.s.read noise,when the illuminance level and pixel area are 1 lux and 1.21 μm2,or 10 000 lux and 0.21 μm2,the recommended integration time is 8.8 to 30 ms,or 10 to 21.3 μs,respectively.The proposed method can guide the design and operation of single-bit and multi-bit QISs.     

山地坡度自适应星载光子计数激光雷达点云去噪方法

星载光子计数激光雷达在接收信号的过程中会产生大量噪声,并且在复杂的山区地形中信噪比低,极大地影响对植被点云信号的准确提取。为解决该问题,提出了一种基于山地坡度的密度聚类算法。通过分析点云数据的密度和森林目标地形特征,用最大密度中心搜索法进行粗去噪,基于点云数据计算坡度角以优化密度聚类,完成数据精去噪。通过对提取的森林区域信号进行分类,拟合植被冠层廓线和地表廓线,结果表明本算法提取植被光子信号的准确率较高,地面与冠层廓线的RMSE分别为0.3588 m和3.7449 m,更适用于植被遥感点云数据处理。     

Electrical, structural, and optical characterization of free-standing GaN template grown by hydride vapor phase epitaxy

Electrical, structural, and optical properties of a free-standing 200 μm thick n-type GaN template grown by hydride vapor phase epitaxy have been investigated. Hall mobilities of 1100 and 6800 cm²/V s have been obtained at room temperature and 50 K, respectively. Quantitative analysis of acceptor concentration, donor concentration and donor activation energy has been conducted through simultaneous fitting of the temperature dependent Hall mobility and carrier concentration data which led to a donor concentration of 2.10×10¹⁶ cm⁻³ and an acceptor concentration of 4.9×10¹⁵ cm⁻³. The resultant donor activation energy is 18 meV. The analysis indicates that the dominant scattering mechanism at low temperatures is by ionized impurities. The extended defect concentrations on Ga- and N-faces were about 5×10⁵ cm⁻² for the former and about 1×10⁷ cm⁻² for the latter, as revealed by a chemical etch. The full width at half maximum of the symmetric (0 0 0 2) X-ray diffraction peak was 69″ and 160″ for the Ga- and N-faces, respectively. That for the asymmetric (10–14) peak was 103″ and 140″ for Ga- and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga- and N-face (after a chemical etch to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.45 eV.     

基于消息传播的LDPC码环统计算法

基于节点间的外部消息传播机制,提出一种新的LDPC码环统计算法,使用和积算法处理消息传播的过程,可有效地统计Tanner图中长度为g,g＋2,…,2g-2的环的数量,其中g为围长。与现有方法相比,本算法复杂度较低,特别适合于围长较长的LDPC码。     

光子累计方法在成像激光雷达中的应用研究

介绍了一套自行研制的采用光子计数探测的1064nm激光雷达系统。理论分析了光子计数探测技术和信噪比的改善．实验研究了改善信噪比的脉冲累计方法。给出了光子累计脉冲与信噪比之间的平方根关系,以及不同距离下的探测结果。另外,讨论了光子累计在两种成像方式下,相同参数的数值模拟和比较。结果表明：采用大发射光束和光子累积方法进行探测的信噪比,比单光束、大光强和逐行扫描方式的探测在理论上要好些。即探测概率高。     

不同通量条件下光子计数激光雷达信号畸变的规律研究

光子计数激光雷达在高通量条件下的输出信号会出现严重的畸变现象,从而影响目标信息的提取,因此,研究信号畸变的变化规律是一个重要的理论与实践问题。为此本文建立了多触发条件下光子计数激光雷达信号计算的稳态正向递推模型,该模型具有精度高、速度快,且可准确反映物理过程等显著优势。结合正确性验证,通过改变模型的信号幅度N、脉冲宽度P_W、背景噪声N_b和死区时间T_d等参数对激光雷达信号畸变的影响规律进行探究,结果表明：当死脉比R_dp≤2时,信号的畸变与N、P_W、T_d有关,当R_dp>2时,信号畸变仅与N有关;同时在仿真实验结果中发现,当探测损失率α≤5%时,可忽略信号畸变的影响,该发现可作为区分高通量信号畸变(α>5%)与低通量信号保真(α≤5%)的判别界限,根据计算,在某些特定条件下,改变死区时间的大小会将高通量转化为低通量。上述结论相比于传统的基于光子计数率的“5%”准则更加精确地划分了高低通量与信号畸变的界限。     

Chemical-bonding structure of InP surface in MOVPE studied by surface photo-absorption

Using surface photo-absorption spectra, we established a phase diagram of the surface chemical-bonding structure for the P-stabilized surface in InP metalorganic vapor phase epitaxy as a function of substrate temperature and PH₃ partial pressure. At 550°C and PH₃ partial pressures of 10 and 30 Pa, the surface is (2 × 4)-like consisting of P dimers having a bond axis parallel to [110]. As the substrate temperature decreases and the PH₃ partial pressure increases, amorphous P species start to adsorb excessively on (2×4)-like P dimer surface. A c(4 × 4)-like surface was not observed. From InP growth experiments for each P surface phase, we found that, to obtain high-quality InP epitaxial layers, excess P adsorption should be suppressed by minimizing the formation of native defects.     

Metalorganic vapor phase epitaxial growth,characterization and annealing experiments on InP doping superlattices

InP doping superlattices (DSLs) were grown by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) and their stability was examined by annealing at high temperatures. Diethylzinc (DEZ) and H₂S were used asp- andn-type doping sources, respectively. Photoluminescence (PL) measurements performed on as grown layers show a shift of the main emission peak with increasing excitation power in very good agreement with theoretical models. A comparison of the PL results between these structures and the annealed samples show that even at very high temperatures (up to 850° C) the tunability of the effective bandgap of the annealed superlattices is possible, although less pronounced than for the as grown layers. This is due to diffusion of the dopants, into adjacent layers and partial compensation of each other. Secondary ion mass spectrometry (SIMS) done on the as grown and annealed samples shows that only the Zn atoms diffuse. Diffusion coefficients obtained from the SIMS profiles give values in the range 1 × 10⁻¹⁴ <D < 9 × 10⁻¹⁴ cm²/s, still smaller than other published values estimated on layers, which did not suffer any treatment. This shows the high quality and stability of our layers even at high temperatures.     

Elastic strains in heteroepitaxial ZnSe1−xTex on InGaAs/InP (001)

Here we report on the elastic strains in ZnSe_1−xTe_x (x<0.9) epitaxial layers grown using photo-assisted metalorganic vapor phase epitaxy on In_0.53Ga_0.47As/InP (001) substrates. High-resolution x-ray diffraction was used to determine their composition and strain. At room temperature, we observed an apparent asymmetry in strains for tensile and compressive layers. However, when we accounted for the difference in thermal expansion between the substrate and epitaxial material, the growth temperature strain relaxation appears symmetric with respect to the sign of mismatch. The growth temperature strains are in agreement with the Matthews and Blakeslee (MB) model [J.W. Matthews and A.E. Blakeslee, J. Cryst. Growth 27, 118 (1974)] for both compressive (x>0.6) and tensile (x<0.4) layers. However, for the layers with composition in the range 0.4<x<0.6, the growth temperature strains exceed the values predicted by the MB theory. Apparently, low-mismatch layers experience a kinetic barrier to relaxation. The overall behavior can be fit by the relaxation model of Dodson and Tsao [B.W. Dodson and J.Y. Tsao, Appl. Phys. Lett. 51, 1325 (1987)] using the values Cμ²=80 s⁻¹ and γ₀=10⁻⁹.     

Metalorganic vapor phase epitaxy of InP using the novel P-source ditertiarybutyl phosphine (DitBuPH)

In this study, the use of a novel phosphorous precursor for low pressure metalorganic vapor phase epitaxy (LP-MOVPE) application has been investigated. Ditertiarybutyl phosphine ((C₄H₉)₂-P-H, DitBuPH) as substitute for the standardly used hydrid gas phosphine (PH₃) promises apart from strongly reduced toxicity due to the reduction of P-H bonds, an enhancement in cracking efficiency as well as a reduction in growth temperature. Layer quality has been examined by means of optical and scanning electron microscopy (SEM), temperature-dependent van der Pauw Hall as well as photoluminescence (PL) measurements. Uncompensated n-type InP-layers (1.0 x 1.5 cm^-3; 59600 cm²Vs)^-1 at 77K) are realized using DitBuPH in combination with commercial TMIn. All results are compared with those obtained by using PH₃ and commercial tertiarybutyl phosphine (TBP) as P-source, respectively.     

Optical and crystallographic properties of high perfection InP grown on Si(111)

The growth of InP by low-pressure metalorganic chemical vapor deposition on vicinal Si(111), misoriented 3° toward [1-10], is reported. Antiphase domain-free InP is obtained without any preannealing of the Si substrate. Crystallographic, optical, and electrical properties of the layers are significantly improved as compared to the best reported InP grown on Si(001). The high structural perfection is demonstrated by a full width at half maximum (FWHM) of 121 arcs for the (111) Bragg reflex of InP (thickness = 3.4 μm) as obtained by double crystal x-ray diffraction. The low-temperature photoluminescence (PL) efficiency is 70% of that of homoepitaxially grown InP layers. The FWHM of the near-gap PL peak is only 2.7 meV as compared to 4.5 meV of the best material grown on Si(001). For the first time, InP:Fe layers with semi-insulating characteristics (ρ > 3 × 10⁷ Ω-cm) have been grown by compensating the low residual background doping using ferrocene. Semi-insulating layers are prerequisite for any device application at ultrahigh frequencies.     

Crowd counting in complex scenes based on an attention aware CNN network

Crowd counting with density estimation has been an active research community due to its significant applications in the fields of public security, video surveillance, traffic monitoring. However, Crowd counting for congested scenes often suffers from some obstacles including severe occlusions, large scale variations, noise interference, etc. In this paper, using the first ten layers of a modified VGG16 and dilated convolution layers as the framework, we have proposed a CNN based crowd counting and density estimation model improved by the attention aware modules with residual connections. To tackle the problem of noise interference, convolutional block attention modules have been introduced into the deep network to segment the foreground and background to focus on interest information, refining deeper features of the input image. To improve information transmission and reuse, residual connections are utilized to link 3 attention blocks. Meanwhile, dilated convolution layers keep larger reception fields and obtain high-resolution density maps. The proposed method has been evaluated on three public benchmarks, i.e. Shanghai Tech A & B, UCF-QNRF and MALL, achieving the mean absolute errors of 64.6 & 8.3, 113.8 and 1.68, respectively. The results outperform some existing excellent approaches. This indicates that the proposed model has high accuracy and better robustness, which is suitable for crowd counting and density estimation in various congested scenes.     

星载光子计数激光测高植被冠层高度误差分析

通过建立植被的单光子探测模型,分析和计算了星载光子计数激光测高植被探测中,因单光子探测原理引起的植被冠层高度误差.实验表明,北方针叶林的星载光子计数测高中单次激光脉冲首次探测到的信号光子的平均高程低于LIDAR数据提供的DSM约2.435 m.仿真结果表明,提高发射脉冲能量,减小激光脉冲发散角有助于减小误差,而拥有更高...     

On the role of interface properties in the degradation of metalorganic vapor phase epitaxially grown Fe profiles in InP

Fe doping profiles in InP layers grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) were investigated by secondary ion mass spectroscopy. Different pre-treatments of the InP substrates proved to have substantially different effects on the Fe profiles which strongly indicate the relevance of underlying interfaces to dopant diffusion in subsequent layers, at least in the case of dopants occupying the group-III sublattice. We attribute the degradation of Fe profiles observed for some kinds of treatment to the emission of In interstitials from surfaces covered by oxides or other residues which are incompletely removed during the MOVPE preheat cycle. A favorable substrate preparation method for avoiding Fe profile degradation relies on etching by 5:1:1 H₂SO₄:H₂O₂:H₂O at room temperature followed by 30 min deionized water rinsing.     

基于Hausdorff距离的行人跟踪计数方法

运用目标匹配和目标链,对视频中的行人进行跟踪和计数。提出了一种基于Hausdorff距离的快速目标匹配方法,利用快速匹配形成的聚类进行最佳匹配,通过目标运动速度和方向的光滑性度量来建立每个运动目标的“目标链”即运动轨迹,实验结果表明此方法保证了运动跟踪的连续性和行人计数的有效性。