A new approach for modeling of dark current characteristics of quantum wire infrared photodetectors

In order to study the dark current characteristics in a quantum wire infrared photodetector(QRIP),the average number of electrons in quantum wires(QRs) must be got,which is mostly too complicated.In this paper we give a simple formula to calculate the average number of carriers in a quantum wire(QR) that can be easily evaluated by mathematical softwares,and then we use this formula to study dark current characteristics of a quantum wire infrared photodetector(QRIP). 更多还原     

Light coupling characteristics of corrugated quantum-well infrared photodetectors

Corrugated quantum-well infrared photodetectors (C-QWIPs) offer simple detector architectures for large-format infrared focal plane arrays (FPAs). The detector relies on inclined sidewalls to couple normal incident light into the absorbing material. Based on a simplified geometrical-optics (GO) model, this light coupling scheme is expected to be effective with little wavelength dependence. In this work, we apply the modal transmission-line (MTL) modeling technique to study in detail its light coupling characteristics and compare the results with the GO model and experimental data. We find that the results of the GO model agree reasonably well with those of the rigorous MTL model for corrugations with metal cover, and both modeling procedures are consistent with experimental data. In particular, both models predict similar increase in the quantum efficiency /spl eta/ with the size of the corrugations, and both indicate similar limiting /spl eta/ when the corrugation becomes very large. For linear corrugations with thick substrates, the maximum /spl eta/ is about 30%. On the other hand, there are also significant differences between the two models when the effects of phase coherence are important. Since the phase of the radiation is taken into account in the MTL formalism but not in the GO formalism, the MTL model is more generally applicable and is more capable of explaining different detector characteristics. For example, it predicts a smaller /spl eta/ for air or epoxy-covered C-QWIPs because of finite optical transmission through the sharp corners in the corrugations, and it indicates an oscillatory function of /spl eta/ because of the existence of optical fringes. It also reveals the wavelength dependence of the coupling, which becomes more pronounced as the thickness of the substrate layer is reduced.     

发光量子阱对波长上转换红外探测器效率的影响

波长上转换红外探测器在实现大面阵、低暗电流红外探测方面具有很大的发展潜力.短波长光子的发光效率是影响上转换器件效率的重要因素.设计、制作了具有不同发光阱个数的波长上转换红外探测器件,结合器件的红外响应和仿真计算,分析了发光阱个数对波长上转换效率的影响规律.研究结果表明,选择单个发光阱,有利于提高器件的发光效率,从而提高波长上转换效率.     

Refined model for the current-voltage characteristics of quantum-well infrared photodetectors

The temperature dependences of the dark current of quantum-well infrared photodetectors are investigated experimentally. It is established that the pre-exponential factor in the analytical expression for the photodetector current-voltage characteristics varies linearly with temperature. On the basis of the results obtained, it is suggested that the temperature dependence of the photodetector??s dark current is determined by the thermal excitation of charge carriers to a band characterized by a two-dimensional density of states. In the context of this suggestion, a refined model for the current-voltage characteristics is proposed. The model takes into account the thermal generation of charge carriers in a band with a two-dimensional density of states and the electric field dependence of the thermal activation energy for the quantum-well ground state and of the drift velocity of the carriers in the barrier conduction band.     

Low frequency noise spectroscopy in InAs/GaAs resonant tunneling quantum dot infrared photodetectors

We have studied the temperature dependence of low-frequency noise in InAs–GaAs resonant tunneling quantum dot infrared photodetectors (T-QDIPs). The noise in these devices has been investigated in the temperature range of 78–300 K. The noise spectrum showed a weak Lorentzian component superimposed upon the 1/f^γ spectrum. The change in the cut-off frequency of the Lorentzian was analyzed as a function of temperature. The activation energy of the trap associated with this Lorentzian was obtained as 0.155 eV, which is in good agreement with the energy of the lowest energy state in the quantum dot.     

（英）量子点红外探测器的光电流和响应率

通过考虑光电导增益对探测器所加电压的依赖性改进了包含电子持续势能和总电子传输的光电流模型,并进一步将这个改进的模型用于估算探测器的响应率.相应的计算结果与公布的结果相比较,具有很好的一致性,证明了改进模型的正确性.     

量子阱红外探测器最新进展

量子阱红外探测器(QWIP)自从20世纪80年代被验证后,得到了广泛积极的研究。基于Ⅲ-Ⅴ材料体系、器件工艺的成熟和自身的稳定性、响应带宽窄等特有的优势,QWIP成为对低成本、大面阵、双(多)色高精度探测有综合要求的第三代红外焦平面阵列(FPA)的重要发展方向。本文主要总结了国际QWIP器件的最新发展动态,并展望了其发展趋势。     

AlGaN日盲紫外雪崩光电探测器暗电流研究

为了提高AlGaN日盲紫外雪崩探测器的信噪比,降低暗电流,研制高性能日盲紫外探测器,针对AlGaN日盲紫外雪崩探测器暗电流机制进行了深入研究。首先对传统p-i-n-i-n结构雪崩探测器进行了初步研究,分别设计了GaN和AlGaN的两种雪崩探测器模型,分析了其不同暗电流特性,得到的模拟暗电流特性曲线与实验吻合。在此基础上,针对日盲紫外波段高Al组分AlGaN雪崩探测器,重点分析研究了不同异质界面的负极化电荷、p型有效掺杂以及温度等因素对暗电流的影响。在AlGaN日盲紫外雪崩探测器研究中得到的近零偏工作暗电流为2.510-13 A,在反向138 V左右发生雪崩击穿,雪崩开启电流为18.3 nA左右,击穿电压温度系数约为0.05 V/K,与实验及文献测试结果吻合。     

Carrier scattering approach to the origins of dark current in mid and far-infrared (terahertz) quantum-well intersubband photodetectors(QWLPs)

A carrier scattering approach is taken in an analysis of the affect on the dark current of extending the operating wavelength of conventional bound to continuum quantum-well intersubband photodetectors. It is found that both the sequential tunneling and the thermionic emission contributions to the dark current increase as the wavelength of the detector is extended from the mid- to far-infrared. Dark current designs rules are derived     

High responsivity InP-InGaAs quantum-well infrared photodetectors: characteristics and focal plane array performance

We report the detailed characteristics of long-wavelength infrared InP-In/sub 0.53/Ga/sub 0.47/As quantum-well infrared photodetectors (QWIPs) and 640/spl times/512 focal plane array (FPA) grown by molecular beam epitaxy. For reliable assessment of the detector performance, characterization was performed on test detectors of the same size and structure with the FPA pixels. Al/sub 0.27/Ga/sub 0.73/As-GaAs QWIPs with similar spectral response (/spl lambda//sub p/=/spl sim/7.8 /spl mu/m) were also fabricated and characterized for comparison. InP-InGaAs QWIPs (20-period) yielded quantum efficiency-gain product as high as 0.46 under -3-V bias with a 77-K peak detectivity above 1/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W. At 70 K, the detector performance is background limited with f/2 aperture up to /spl sim/ 3-V bias where the peak responsivity (2.9 A/W) is an order of magnitude higher than that of the AlGaAs-GaAs QWIP. The results show that impact ionization in similar InP-InGaAs QWIPs does not start until the average electric-field reaches /spl sim/25 kV/cm, and the detectivity remains high under moderately large bias, which yields high responsivity due to large photoconductive gain. The InP-InGaAs QWIP FPA offers reasonably low noise equivalent temperature difference (NETD) even with very short integration times (/spl tau/).70 K NETD values of the FPA with f/1.5 optics are 36 and 64 mK under bias voltages of -0.5 V (/spl tau/=11 ms) and -2 V (/spl tau/=650 /spl mu/s), respectively. The results clearly show the potential of InP-InGaAs QWIPs for thermal imaging applications requiring high responsivity and short integration times.     

带间级联红外探测器的光电流输运与量子效率研究

带间级联红外探测器可以利用多级吸收区级联的方式实现高的工作温度,但不同的吸收区厚度设计方式会使得器件在不同级数吸收区中出现光生载流子的不匹配现象,从而对器件量子效率造成影响。为更好地理解带间级联探测器的级数和吸收区厚度对量子效率的影响,对基于InAs/GaSb II类超晶格的带间级联探测器进行了变温测试,并基于多级光电流的“平均效应”建立了工作在反向偏置电压的量子效率计算模型,通过与实际测试的量子效率对比,发现在低温条件下实验数据和计算结果拟合一致性较好,验证了多级带间级联探测器中基于内增益机制的光电流平均效应。但在高温条件下,实际的光电流低于“平均效应”的理论计算结果,这可能是由于高温下少数载流子寿命变短,在吸收区和弛豫区界面处存在光生载流子的复合机制。     

太赫兹量子阱探测器性能研究及提高

提出了一个砷化镓基(GaAs/Al_(0.04)Ga_(0.96)As)太赫兹量子阱探测器,并对其光电流谱和背景噪声限制温度进行了表征,得到峰值响应频率为6.78 THz,背景噪声限制温度为16 K.理论上,首先,考虑多体效应对器件能带结构的影响,计算得峰值响应频率为6.64 THz,考虑到制备过程中的误差(THz器件较中红外器件,铝组分低,阱宽窄),理论与实验吻合的较好,证实了多体效应在太赫兹量子阱探测器中的重要影响;然后,对器件的电流电压特性进行研究,计算得到背景噪声限制温度为17.5 K,与实验吻合.太赫兹量子阱探测器较低的工作温度,极大限制了其应用,提出了两种实现高温探测的方法:(1)引入光学汇聚天线,提高器件背景限制温度,计算结果表明当引入增强系数为10~6倍的天线时,其背景噪声限制温度达到97 K(远高于液氮温度77 K);(2)太赫兹量子阱探测器与太赫兹量子级联激光器联用,可实现信号噪声限制模式,从而实现高温探测.计算表明,当激光器功率达到0.003 mW/μm~2,器件的工作温度可达77K.     

KOH溶液处理对AlGaN紫外探测器暗电流的影响

采用KOH溶液表面处理工艺制备得到了128×1线列日盲AlGaN紫外探测器,器件的反偏暗电流为6.88×10-9A(-8 V时),比未采用此项工艺制备得到的器件的暗电流减小近103倍。元素深度分布俄歇电子谱(AES)等测试结果分析表明,采用这种表面处理工艺可以有效地去除干法刻蚀后材料表面的N空位、刻蚀生成物及自然氧化物,减小了界面态密度,改善了电流-电压特性,减小了反偏暗电流。利用传输线模型TLM计算得到了Ti/Al/Ti/Au金属电极与高Al组分n-Al0.65Ga0.35N材料间的接触电阻率为8.35×10-3Ωcm2。     

Transparent photodetectors with ultra-low dark current and high photoresponse for near-infrared detection

A remarkable progress in research works regarding flexibility and transparency of organic optoelectronic devices has been observed in the past decade compared to their inorganic counterparts. However, few studies have been devoted to the advancement of a transparent organic photodetector. In this study, we have used a wavelength-selective bulk-heterojunction of ClAlPc:C₆₀ as active layer and Cu:Ag/WO₃ metal alloy as electrode to realize a see-through organic photodetector (OPD) with an average visible transmission of 76.92%. The optimized transparent OPDs show an average dark current density of 0.36 nA cm⁻² and a rise/fall time of <5 μs under a bias voltage of −2 V, which could be potentially applied in a home security system based on invisible near-infrared detection.     

Comparison of hole and electron intersubband absorption strengthsfor quantum well infrared photodetectors

It is well known that the hole intersubband absorption of normally incident (TE polarized) radiation is nonzero for p-doped quantum well infrared photodetectors (p-QWIP's) which have been fabricated without an optical grating. This present paper shows from k&oarr;·p&oarr; theory that, for typical p-QWIP designs, this hole intersubband absorption of TE polarized radiation (without the help of an optical grating) is significantly smaller than the electron intersubband absorption of TE polarized radiation in those n-doped QWIP's (n-QWIP's) fabricated with an optical grating. A second result of this present work is that, even when there is significant mixing of the light and heavy hole states, the p-QWIP absorption of TE polarized radiation (without the help of an optical grating) is still much smaller than the n-QWIP absorption of TE polarized radiation (with the help of an optical grating). The reason is that the mixing of light and heavy hole states never increases the amount of |S〉-symmetry in the mixed hole wave function beyond the amount of |S〉-symmetry which was present in the unmixed, purely light hole state. Finally, this present paper shows from k&oarr;·p&oarr; theory that strained layer growth on an (001) substrate does not significantly affect the strength of the hole intersubband absorption. The reason is that the Hamiltonian describing uniaxially strained quantum wells has precisely the same (tetragonal) symmetry as the Hamiltonian describing carrier confinement in unstrained quantum wells. All of these results are important in choosing a QWIP device design     

Design and characterization of a CMOS preamplifier for quantum well infrared photodetectors

A preamplifier based on the source-follower direct injection (SFDI) topology for use in read-out integrated circuits (ROIC) of quantum-well infrared photodetectors focal plane arrays (QWIP-FPA) is demonstrated. The fabricated circuit shows high linearity, high integration time (from hundreds of μs to few ms) and low current detection capabilities for a wide range of input current (order of few pA). This performance was achieved through the use of a Poly1-Poly2 capacitor that, although presenting some penalties in area consumption, provides a higher linearity, lower leakage current and higher temperature stability than all others capacitors found in literature. Secondary effects such as charge injection and clock feed-through are observed in the experimental results and classical techniques, like the use of DUMMY transistor, are shown to be effective in minimizing these effects and maximizing the linearity of the response. The overall results indicate that this circuit architecture has a great potential to be practically integrated in larger QWIP-FPA ROICs, showing an improved performance relating to previous works in literature.     

改进器件工艺降低硅光电探测器暗电流

为降低硅光电探测器ＰＮ结反向暗电流，可在器件制作工艺中采用一系列完美晶体器件工艺（ＰＣＤＴ）。在实验过程中，对吸除工艺，应力补偿工艺等作了改进，进一步降低了反向暗电流。     

InAsSb势垒阻挡型红外探测器暗电流特性研究

计算了不同温度下由辐射复合和俄歇复合决定的InAsSb材料的载流子寿命,结果表明,低温下n型InAsSb材料的载流子寿命受限于辐射复合过程,而高温下InAsSb材料的载流子寿命取决于Auger 1复合过程。讨论了势垒阻挡型器件的暗电流解析模型及暗电流抑制机理,通过在nBn吸收层的另一侧增加重掺杂的n型电极层形成nBnn⁺结构对吸收区内的载流子进行耗尽,吸收区少数载流子浓度降低约两个数量级,从而进一步降低器件暗电流。成功制备了InAsSb-基nBnn⁺器件,150 K下器件暗电流低至3×10^-6 A/cm²,采用势垒结构器件的暗电流解析模型对150 K下器件的暗电流进行拟合分析,结果表明由于势垒层为p型掺杂,在吸收层形成耗尽区,导致器件中的产生复合电流并没有完全被抑制,工作温度低于180 K,器件暗电流受限于产生复合电流,工作温度高于180 K,器件暗电流受限于扩散电流。     

Low dark current and internal gain mechanism of GaN MSM photodetectors fabricated on bulk GaN substrate

Metal-semiconductor-metal ultraviolet photodetectors are fabricated on low-defect-density homoepitaxial GaN layer on bulk GaN substrate. The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is ∼5 × 10⁶ cm⁻². The photodetector with a high UV-to-visible rejection ratio of up to 1 × 10⁵ exhibits a low dark current of <2 pA at room temperature under 10 V bias. The photo-responsivity of the photodetector gradually increases as a function of applied bias, resulting in a photodetector quantum efficiency exceeding 100% at above medium bias. The photo-responsivity also shows a dependence on the incident optical power density and illumination conditions. The internal gain mechanism of the photodetector is attributed to photo-generated holes trapped at the semiconductor/metal interface as well as high-field-induced image-force lowering effect.     

太赫兹量子阱探测器的暗电流抑制电路研究

主要研究了太赫兹量子阱探测器读出电路中的暗电流抑制模块。首先从理论上分析了太赫兹量子阱探测器产生暗电流和光电流的原理。由于太赫兹量子阱探测器中电子输运行为非常复杂,难以通过理论推导建立精确等效电路模型的解析表达式。通过对太赫兹量子阱探测器的电流电压实验数据进行拟合,提出压控电流源等效电路模型。利用此模型设计读出电路信号源及暗电流抑制模块,结合读出电路进行仿真验证电路模型的准确性。发现与传统暗电流抑制电路相比,压控电流源电路模型能够在器件工作偏压变化时对其暗电流进行精确抑制,提高读出电路性能,因此更适合作为太赫兹量子阱探测器读出电路的暗电流抑制模块。