1-2 micron (Hg, Cd)Te photodetectors

The performance of mercury cadmium telluride detectors in the 1-2 micron spectral region has been predicted from basic material parameters. Photovoltaic devices should be characterized by specific responsivities of 1 A/W for a 1000 ohm load when transit time limited to less than 20 ns. Photoconductive detectors made from n-type material should have radiative lifetimes of 1 ms. The feasibility of high performance 1-2 micron (Hg, Cd)Te detectors has been demonstrated experimentally. Deep junction devices operating at room temperature without bias have been fabricated by impurity indiffusion. Detectivities at 1.75 microns approached 10¹⁰cm.Hz^1/2/W with open-circuit responsivities of approximately 500 V/W. In addition, 1.5 micron detectors have been fabricated from p-type, 25 Ω.cm material. With no bias at room temperature, these detectors showed D* λ>10¹⁰cm.Hz/12/W, open-circuit responsivities in excess of 10³V/W, and response times on the order of microseconds. These preliminary results indicate that detectors fabricated from the pseudobinary alloy of (Hg, Cd)Te are well suited for high speed, near infrared photodetection in which room temperature operation is required.     

红外单光子探测器暗计数的研究

分析暗计数的来源,讨论温度及门控模式下各种参数对暗计数的影响,提出减小暗计数的有效方法。太低的温度不利于暗计数的减小,而应根据不同的APD选择合适的温度并与门控技术结合来消除暗计数。偏置电压的大小、门脉冲宽度和周期的选择对后脉冲的消除起着关键的作用。     

Effect of doped substrate on GaAs-AlGaAs interfacial workfunction IR detector response through cavity effect

In this paper, results are reported showing response enhancement in GaAs-AlGaAs IR detectors using a doped substrate to increase reflection, enhancing the resonant cavity effect. Responsivity for heterojunction interfacial workfunction detectors grown on semi-insulating (SI) and doped substrates are compared. For a device grown on an SI substrate, a 9-/spl mu/m resonance peak had a response of 1.5 mA/W while a similar device on an n-doped substrate showed 12 mA/W. Also, the difference between response under forward and reverse bias (3 versus 12 mA/W) for the sample grown on the doped substrate, as well as calculated results confirm that the increased response is due to the resonant enhancement. An optimized design for a 15-/spl mu/m peak (24 /spl mu/m 0 response threshold) detector grown on a doped substrate could expect a peak response of 4 A/W with a 50% quantum efficiency and D/sup */ /spl sim/ 2 /spl times/ 10/sup 10/ Jones at the background limited temperature of 50 K.     

Analysis of the structure of a terahertz-band 2D array with sensors on the edge of a superconductor transition

Film detectors on the edge of a Ti or Mo/Cu (T _c ≈ 0.4 K) superconductor transition are included in an N × M 2D array of planar polarization-separated antennas. The detectors are simultaneously sensors and absorbers of the total electric power from an antenna and bias circuits. The detectors are heat-insulated because of weak electron-phonon interaction with the substrate and because of the effect of the Andreev reflection of electrons in Nb electrodes. Readout based on the projection method necessitates only N + M channels in the case when the signal is continuously accumulated for all N × M detectors. Simulation of a 3 × 3 2D array at a frequency of 600 GHz shows that the matching band is ～30%.     

Characterization of resonant tunneling diodes for microwave andmillimeter-wave detection

The authors report on the direct detection capabilities of resonant tunneling diodes in the 10-100 GHz range. An open circuit voltage sensitivity of 1750 mV/mW (in Ka-band) was measured. This is higher than the sensitivity of comparatively based commercially available solid-state detectors. The detector properties are a strong function of diode bias and the measured tangential signal sensitivity (-32 dBm at Ka-band with 1-MHz bandwidth) and the dynamic range (25 dB) of the diode are smaller compared to other solid-state detectors     

SiO_2钝化层对GaN基PIN结构核探测器漏电流的影响

成功地制备了有SiO2钝化层和无SiO2钝化层的GaN基PIN结构核辐射探测器,并对二者的I-V特性进行了测试。实验结果表明,SiO2钝化层的存在显著地降低了GaN基PIN结构核辐射探测器的反向漏电流,在-40V的反向偏压情况下,漏电流约有2个数量级的降低。实验过程中观测到随着反向偏压的增大,SiO2钝化层对器件反向漏电流的抑制效应更明显。建立了一种表面沟道模型解释了SiO2钝化层对漏电流的影响。     

The frequency behavior of InGaAs-AlInAs metal-semiconductor-metalphotodetectors at low bias voltages for data communication applications

The authors have fabricated lattice matched InGaAs/AlInAs metal-semiconductor-metal photodetectors on InP. The detectors have very low dark currents, low capacitance, and good responsivity, corresponding to at least 95% internal collection efficiency. It is demonstrated that multigigahertz bandwidths, as measured in the frequency domain, are achievable at typical logic-level bias voltages, and that therefore these detectors are viable candidates for long-wavelength data communication applications     

Cl_2/Ar/BCl_3ICP刻蚀AlGaN的研究

感应耦合等离子体(ICP)刻蚀在AlGaN基紫外探测器台面制作中起着重要作用。在对比了ICP与RIE,ECR等干法刻蚀技术优缺点的基础上,采用Ni作为掩膜,Cl2/Ar/BCl3作为刻蚀气体,对金属有机化学气相淀积生长的n-Al0.45Ga0.55N进行了ICP刻蚀研究。刻蚀速率随着ICP直流偏压的增加而增加,刻蚀速率随着ICP功率的增加先增加较快后增加缓慢。最后结合刻蚀表面的扫描电镜(SEM)分析和俄歇电子能谱(AES)深度分析对刻蚀结果进行了讨论。分析表明,在满足刻蚀表面形貌的同时,较低的直流偏压下刻蚀速率较慢,但损伤较小,这对于制备高性能的紫外探测器是有利的。     

Hg1-xCdxTe metal-semiconductor-metal (MSM)photodetectors

Metal-semiconductor-metal (MSM) detectors with active layers of Hg _1-xCd_xTe (x=0.62-0.74) and electrode spacings of 2, 4, and 6 μm have been fabricated and characterized. Direct-current measurements have shown a low dark current and high responsivity from 0.15 to 1.5 A/W at 10-V bias. The lowest values of dark current (0.16 mA cm²) were obtained for detectors which incorporated an overlayer of CdTe. For detectors without the overlayer, increasing the Cd mole fraction resulted in a decrease in the dark current and a reduction in the 300-nm responsivity. Measurements of frequency response for these detectors show a maximum loss of 8 dB to 20 GHz. These results compare favorably with high-performance MSM detectors based on In_0.53Ga_0.47As with a lattice-matched barrier layer of In_0.52Al_0.48As     

Impedance properties and broad-band operation of GaAs photoconductive detectors

The impedance properties of GaAs ion-implanted photoconductive detectors reveal an interesting effect. The reflection coefficient S11of the photoconductors shows the detector impedance to be a constant resistance with no reactive component over a bandwidth of more than 1.5 GHz at a particular bias voltage. Broad-band matching to the detector load and transit time limited detector response (no RC time constant) are possible due to the absence of reactive components. A model is presented that explains this effect, as well as the superlinear increase in output signal with bias observed with these detectors. Also, no evidence of the long low response tails present in these and similar photoconductors in seen in the S11measurement, lending experimental support to the common theory that these tails are due to the trapping of excess photogenerated minority carries.     

Comparison of GaN and 6H-SiC p-i-n photodetectors with excellentultraviolet sensitivity and selectivity

We fabricated GaN and 6H-SiC p-i-n photodetectors and compared their electrical and optical characteristics. The GaN diodes suffered from significant leakage current of 37 μA/mm² at -5 V, while the SiC diode leakage current was below the noise level at 10 pA/mm² at -20 V. The built-in potentials and the unintentional “i-layer” doping densities were obtained from capacitance-voltage (C-V) measurements. The SiC detectors exhibited a broad spectral response in contrast to the abrupt cutoff observed in the GaN detectors. The peak responsivities of the GaN and SiC photodetectors corresponded to internal quantum efficiencies of 57% at 3.42 eV and 82% at 4.49 eV, respectively. Furthermore, both detectors exhibited excellent visible rejection ratios which is needed for solar-blind applications. The response times at zero bias were 18 and 102 ns for the GaN and SiC detectors, respectively     

Bias sensitive a-Si(C): H multispectral detectors

New types of a-Si(C):H thin-film multispectral detectors were designed and successfully fabricated. It was found that the controlling of drift length in the active regions provides a simple and useful criterion for the design, by the aid of which novel multispectral detectors with ni'pi'δ(n)in or pini'δ(p)ip structure were developed. The device with a ni'pi'(δn)in structure show's spectral response peaks located at 450, 550, and 600 nm under bias voltages of 4.5, -1.5, and -7.0 V, respectively. This response is very similar to that of the human eye. In the corresponding pi'ni'δ(p)ip structure the maximum response can be shifted to 510 nm at a bias of -6.0 V, 560 nm at 1.0 V, and 610 nm at 5.5 V. Moreover, the prototypes exhibit excellent linearity within an illumination range from 10¹¹ to 10¹⁵ photons cm^-2 s^-1 and a high dynamic range of more than 56 dB under illumination of 1000 Ix     

Al‐Doped Black Phosphorus p–n Homojunction Diode for High Performance Photovoltaic

2D layered materials based p–n junctions are fundamental building block for enabling new functional device applications with high efficiency. However, due to the lack of controllable doping technique, state‐of‐the‐art 2D p–n junctions are predominantly made of van der Waals heterostructures or electrostatic gated junctions. Here, the authors report the demonstration of a spatially controlled aluminum doping technique that enables a p–n homojunction diode to be realized within a single 2D black phosphorus nanosheet for high performance photovoltaic application. The diode achieves a near‐unity ideality factor of 1.001 along with an on/off ratio of ≈5.6 × 10³ at a low bias of 2 V, allowing for low‐power dynamic current rectification without signal decay or overshoot. When operated under a photovoltaic regime, the diode's dark current can be significantly suppressed. The presence of a built‐in electric field additionally gives rise to temporal short‐circuit current and open‐circuit voltage under zero external bias, indicative of its enriched functionalities for self‐powered photovoltaic and high signal‐to‐noise photodetection applications.     

激光干扰对红外成像探测器MTF影响的仿真研究

分析了激光辐照对成像探测器的软损伤效应,尤其是成像探测器光学性能的退化效应.通过探测器仿真软件模拟了激光辐照前后的斜缝成像效果,并使用二维傅里叶变换法获得了辐照前后的系统MTF值,证明了激光辐照对MTF的影响.     

Readout schemes for low noise single-photon avalanche diodes fabricated in conventional HV-CMOS technologies

Three different pixels based on single-photon avalanche diodes for triggered applications, such as fluorescence lifetime measurements and high energy physics experiments, are presented. Each pixel consists of a 20 μm×100 μm (width×length) single photon avalanche diode and a monolithically integrated readout circuit. The sensors are operated in the gated mode of acquisition to reduce the probability to detect noise counts interferring with real radiation events. Each pixel includes a different readout circuit that allows to use low reverse bias overvoltages. Experimental results demonstrate that the three pixels present a similar behavior. The pixels get rid of afterpulses and present a reduced dark count probability by applying the gated operation. Noise figures are further improved by using low reverse bias overvoltages. The detectors exhibit an input dynamic range of 13.35 bits with short gated ‘on’ periods of 10 ns and a reverse bias overvoltage of 0.5 V. The three pixels have been fabricated in a standard HV-CMOS process.     

p-GaAs同质结太赫兹探测器的优化与性能

从提高p-GaAs同质结太赫兹探测器量子效率出发,在考虑温度和偏压等参数的影响后,优化了谐振腔增强的p-GaAs同质结太赫兹探测器的材料及结构参数,使探测器的量子效率提高到了17%.并计算了探测器的响应率、探测率和偏压、温度、光谱频率的关系,得到了最佳工作偏压(10~40 m V)、最佳工作温度(8 K)和最大探测率(4.1×1010cm Hz1/2/W).而通过施加一对匹配的反射镜来构造谐振腔的设计,所能获得的极限量子效率为26%,极限探测率和响应率分别为5.7×1010cm Hz1/2/W、25.9 A/W.     

Performance of Ge-on-Si p-i-n Photodetectors for Standard Receiver Modules

Ge on Si p-i-n photodetectors with areas which are compatible with commercially available receivers have been fabricated and tested. A dark current density of 6 mA/cm² at -1-V bias has been measured at room temperature; when heated to 85 degC, the measured dark current increases by a factor of nine. A responsivity of 0.59 A/W at 850 nm has been measured from these Ge detectors, which matches or exceeds commercially available GaAs devices. We have measured bandwidths approaching 9 GHz at -2-V bias from 50-mum diameter Ge detectors, and have observed eye diagrams comparable to those obtained from GaAs-based receivers at 4.25 Gb/s     

Performance of QPET, a high-resolution 3D PET imaging system for small volumes

QPET is a positron imaging system developed at Queen's University for high-resolution, 3D imaging of small volumes; it includes a pair of planar gamma-ray detectors 25.4 cm square, which rotate about a central axis with a quasi-cylindrical geometry. The authors describe the performance of this system. Basic characteristics of the detectors are evaluated: a spatial sampling of 1 mm, a quantum efficiency of 9.3% (for 511 keV gamma rays with normal incidence), and a time resolution of 88 ns. Models are developed to characterize the system deadtime and the sensitivity in terms of the noise-equivalent counting rate. With an 8 cm diameter spherical source, the noise-equivalent counting rate reaches a maximum at just over 3 kcps for an activity concentration of 2 muCi/cc; the random coincidence events and the deadtime losses both contribute significantly and the scatter contribution is small. Spatial resolution and uniformity over the field of view are evaluated by imaging short and long line sources; a spatial resolution of 2.7 mm in the transverse directions and 2.0 mm in the axial direction is achieved, with excellent uniformity throughout the field of view. The detector response is amplitude invariant across a 20 cm transverse diameter and a 9 cm axial length with the acceptance angle limited to +/-25 degrees in the axial direction. As an example of the imaging capabilities of QPET, the authors show 3D images of (18)F uptake in the bones of a rat, showing the excellent spatial resolution. This system is best suited to limited-volume applications where high counting rates are not necessary, but where high spatial resolution and uniform detector response are priorities.     

不同钝化层结构的长波碲镉汞光伏探测器的γ辐照效应

对采用单层ZnS和双层CdTe/ZnS两种钝化层结构的长波碲镉汞光伏器件进行了实时γ辐照效应研究.通过辐照过程中实时测试器件的电流-电压特性,发现随着辐照剂量的增加,两种器件表现出不同的辐照效应.结合光伏器件的电流机制分析,对器件的电阻-电压曲线进行数值拟合,发现器件的主要电流机制在偏压较大时为间接隧道电流,在偏压较小及零偏压附近时为产生-复合电流.对辐照前后器件的电阻-电压曲线进行对比分析,认为CdTe/ZnS双层钝化结构有助于降低辐照位移效应的影响,使得器件间接隧道电流随辐照剂量无明显的增加;同时发现辐照电离效应的影响与器件材料的初始性能参数密切相关,拟合得到ZnS单层钝化结构的器件具有较高的少子产生-复合寿命,受电离效应的影响较大,导致其产生-复合电流随着辐照剂量增加持续增大.     

Monolithic GaInAs/InP photodetector arrays for high-densitywavelength division multiplexing (HDWDM)

Monolithic arrays of interdigitated GaInAs/InP photodetectors have been fabricated for high density wavelength division multiplexing (HDWDM) applications. The detectors typically exhibit a reverse leakage current of 400 nA, capacitance of less than 70 fF and a responsivity of 0.5 A/W at -5 V bias. An optical crosstalk of -33.4 dB has been measured between adjacent detectors in an experimental grating demultiplexer system. Preliminary electrical crosstalk measurements in the frequency range of 1-500 MHz indicate signal isolation of the order of 46 dB