Long wavelength infrared photodetector design based on electromagnetically induced transparency

A novel long-wavelength infrared (IR) photodetector based on Electromagnetically induced transparency (EIT) which is suitable for operation in about room temperature and THz range is proposed and analyzed in detail in this article. The main point in this paper for operation in room temperature is related to convert the incoming long-wavelength IR signal to short-wavelength or visible probe optical field through EIT phenomena. For realization of the idea, we used 4, 5- and 6-level atoms implemented by quantum wells or dots. In the proposed structure long-wavelength IR signal does not interact directly with electrons, but affects the absorption characteristics of short-wavelength or visible probe optical field. Therefore, the proposed structure reduces and cancels out the important thermionic dark current component. So, the proposed idea can operate as long wavelength photodetector.     

Investigation of the quantum dot infrared photodetectors dark current

Quantum dot infrared photodetectors (QDIPs) are more efficient than other types of semiconductor based photodetectors; so it has become an actively developed field of research. In this paper quantum dot infrared photodetector dark current is evaluated theoretically. This evaluation is based on the model that was developed by Ryzhii et al. Here it is assumed that both thermionic emission and field-assisted tunneling mechanisms determine the dark current of QDIPs; moreover we have considered Richardson effect, which has not been taken into account in previous research. Then a new formula for estimating average number of electrons in a quantum dot infrared photodetector is derived. Considering the Richardson effect and field-assisted tunneling mechanisms in the dark current improves the accuracy of algorithm and causes the theoretical data to fit better in the experiment. The QDIPs dark current temperature and biasing voltage dependency, contribution of thermionic emission and field-assisted tunneling at various temperatures and biasing voltage in the QDIPs dark current are investigated. Moreover, the other parameter effects like quantum dot (QD) density and QD size effect on the QDIPs dark current are investigated.     

Detector and readout performance goals for quantum well and strained layer superlattice focal plane arrays imaging under tactical and strategic backgrounds

Advancements in III–V semiconductor based, Quantum-well infrared photodetector (QWIP) and Type-II Strained-Layer Superlattice detector (T2SLS) technologies have yielded highly uniform, large-format long-wavelength infrared (LWIR) QWIP FPAs and high quantum efficiency (QE), small format, LWIR T2SLS FPAs. In this article, we have analyzed the QWIP and T2SLS detector level performance requirements and readout integrated circuit (ROIC) noise levels for several staring array long-wavelength infrared (LWIR) imaging applications at various background levels. As a result of lower absorption QE and less than unity photoconductive gain, QWIP FPAs are appropriate for high background tactical applications. However, if the application restricts the integration time, QWIP FPA performance may be limited by the read noise of the ROIC. Rapid progress in T2SLS detector material has already demonstrated LWIR detectors with sufficient performance for tactical applications and potential for strategic applications. However, significant research is needed to suppress surface leakage currents in order to reproduce performances at pixel levels of T2SLS FPAs.     

一种减小GaN基肖特基结构紫外探测器暗电流的方法

提出了一种减小GaN肖特基结构紫外探测器暗电流的方法.该方法是在普通的GaN肖特基结构的表面增加一层薄的p-GaN.模拟计算结果表明,该层p-GaN能增加肖特基势垒高度,从而减小了器件的暗电流,提高了器件性能.进一步的计算还发现,对于p型载流子浓度较高的情况下,只需要很薄的一层p-GaN就能显著增加肖特基势垒高度,对于p型载流子浓度较低的情况下,则需要较厚的一层p-GaN才能有较好的肖特基势垒高度增加效果. 关键词： GaN 肖特基结构 紫外探测器 暗电流     

The transition mechanisms of quantum-dot/quantum-well mixed-mode infrared photodetectors

The transition mechanisms of a 10-period quantum-dot (QD)/quantum-well (QW) mixed-mode infrared photodetector is investigated in this paper. Both mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) responses are observed for the device. The lower normal incident absorption of the LWIR peak suggests that the QW intra-band transition is responsible for the response while the QD intra-band transition for the MWIR response. Due to the coexistence of MWIR and LWIR responses, the MWIR response should be resulted from one-photon transition while the LWIR response from the two-photon transition. To explain the transition mechanisms of the MMIP device, a model is proposed in this paper. The increases of both MWIR and LWIR responses with increasing measurement temperatures observed for the device are attributed to the increase of electrons in the QW ground state/wetting layer state resulted from the increase of one-photon absorption process with increasing temperatures.     

Ultra-wide-band long-wavelength photodetectors

Developments and performances of ultra-wide-band long-wavelength photodetectors are outlined. Theoretical consideration shows the competence of the waveguide p-i-n photodetector for ultra-wide-band long-wavelength optical fibre communication. A newly proposed multimode waveguide p-i-n photodetector with mushroom-mesa structure can relax the parasitic limits, and reaches a record performance of 110 GHz bandwidth and 50% external quantum efficiency at a 1.55 m wavelength. A high-speed monolithically integrated photoreceiver using the waveguide p-i-n photodetector is also presented.     

Towards dualband megapixel QWIP focal plane arrays

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024 × 1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95 K operating temperature with f/2.5 optics at 300 K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70 K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90 K and 70 K operating temperatures respectively, with similar optical and background conditions. In addition, we have demonstrated MWIR and LWIR pixel co-registered simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024 × 1024 pixel arrays and the progress of dualband QWIP focal plane array development work.     

Development of long-wavelength infrared detector and its space-based application requirements

Infrared detection technology has greatly expanded the ability of mankind to study the earth and the universe. In recent years, the demand for long-wavelength infrared detectors is increasing for their advantages in exploring the earth and the universe. A variety of long-wavelength infrared detectors have been made based on thermal resistive effect, photoelectric effect, etc., in the past few decades. Remarkable achievements have been made in infrared materials, device fabrication,readout circuit, and device package. However, high performance long-wavelength infrared detectors, especially those for large format long-wavelength infrared detector focus plane array, are still unsatisfactory. Low noise, high detectivity, and large format long-wavelength infrared detector is necessary to satisfy space-based application requirements.     

Responsivity–dark current relationship of quantum dot infrared photodetectors (QDIPs)

We studied the responsivity–dark current relationship of quantum dot infrared photodetector (QDIP) devices published by several research groups. We found that the dark currents (I_ds) of these devices increased in proportion to the square of responsivity (R). Taking into consideration the photoconductive gain (g), which is considered to be equivalent to the noise gain (g_n), we found that this proportionality was because g (and g_n) is proportional to the square root of I_d. This result indicates that, in order to improve a device’s signal-noise characteristics, it is essential to improve its internal quantum efficiency.     

Novel differentially strained p-doped quantum well infrared detector

We propose a differentially strained p-doped quantum well infrared (IR) photodetector that achieves high performance specifications. We examine key device and material considerations for such a detector for near 10 μm detection. We calculate that through differential strain, this novel detector has improved gain and substantially reduced dark current over previous quantum well IR photodetectors, while being able to detect normal incident light.     

Modulation transfer function of QWIP and superlattice focal plane arrays

Modulation transfer function (MTF) is the ability of an imaging system to faithfully image a given object. The MTF of an imaging system quantifies the ability of the system to resolve or transfer spatial frequencies. In this paper we will discuss the detail MTF measurements of a 1024 × 1024 pixel multi-band quantum well infrared photodetector and 320 × 256 pixel long-wavelength InAs/GaSb superlattice infrared focal plane arrays.     

Dark current suppression in an erbium-germanium-erbium photodetector with an asymmetric electrode area

In this work, suppression of the dark current level in a metal-semiconductor-metal (MSM) photodetector fabricated on the intrinsic (i) Ge is achieved by exploiting (1) the Er electrode, providing a relatively high hole barrier, and (2) the concept of asymmetric electrode area, to minimize the Schottky barrier height lowering effect. Compared with a symmetric MSM photodetector fabricated with Ti electrodes, the dark current level was reduced by a factor of about 80. This low dark current i-Ge MSM photodetector is promising for applications requiring low power and a high photo-to-dark-current ratio.     

量子点红外探测器在空间光电系统中的应用

为了更好地开发和利用空间资源,各国竞相通过向空间发射卫星、空间站、航天飞机等航天器来建立探测站点和通信网络以占据具有最大优势的位置,其中空间光电系统在探索新资源方面起到关键的作用.点对点的距离远、空间辐射强、温差较大等空间环境因素严重影响着光电系统性能的发挥,也向空间光电系统的稳定性和可靠性提出了挑战.本文提出将具有较高的探测灵敏度、工作温度、抗辐射能力和响应带宽的新型量子点红外探测器应用于空间光电系统,阐述了量子点红外探测器的基本工作原理和优点,并讨论了量子点红外探测器在空间应用的技术要求,分析了其在空间的激光雷达、卫星光通信和成像或者非成像系统中的应用.     

Excess noise in InAs/GaSb type-II superlattice pin-photodiodes

We characterize the low-frequency white noise behavior of a large set of InAs/GaSb superlattice infrared pin-photodiodes for the mid-wavelength infrared regime at 3–5 μm. For diodes with an increased dark current in comparison to the dark current of generation–recombination limited bulk material, the standard shot-noise model fails to describe the noise experimentally observed in the white part of the spectrum. Instead, we find that McIntyre’s noise model for avalanche multiplication processes is compliant with our data. We suggest that within high electric field domains localized around macroscopic defects, avalanche multiplication processes leading to increased dark current and excess noise.     

Low-frequency noise characteristics of InGaAs quantum-dot infrared photodetector structures grown by atomic layer molecular-beam epitaxy

Optical and electrical characteristics of n–i–n InGaAs/GaAs quantum-dot (QD) infrared photodetectors are reported. In particular, the low-frequency excess electrical noise is measured at room temperature and analyzed in conjunction with the optical properties of the structure. The three stackings of QD were formed by atomic layer molecular-beam epitaxy and highly Si-doped, and AlGaAs current-blocking layer was also included to reduce the dark current. The power-dependent photoluminescence (PL) spectra at 300 K indicates that there are at least three confined states in the QD. The photo-current was observed only at low temperatures (10 K) at wavelengths between 3 and 9 μm with three peaks. The dark current was relatively large and asymmetric at low temperatures. At room temperature the dark current was symmetric and ohmic. The 1/f-like low-frequency noise spectral density exhibited an almost quadratic current dependence giving a large value of the Hooge parameter of the order of unity. The relatively low-growth temperature for the AlGaAs current blocking layer and the high doping at the quantum dots seem to generate a considerable amount of defects and result in low-temperature photodetection and a large low-frequency noise density.     

碲镉汞焦平面光伏器件的实时γ辐照效应研究

对碲镉汞长波和中波焦平面光伏器件进行了实时γ射线辐照效应研究,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,中波器件比长波器件表现出更好的抗辐照能力.对于长波器件,随着辐照剂量的增大,能够反映器件性能的零偏电阻逐渐降低;对于中波器件,零偏电阻随着辐照剂量的增加无固定变化趋势,辐照效应主要表现在电阻-电压曲线随着辐照剂量增加出现越来越明显的扰动.根据光伏器件的暗电流机理,对长波器件的电阻-电压曲线进行数值拟合,发现辐照引起少子产生-复合寿命逐渐降低,缺陷密度逐渐增大,主要影响的电流机理 关键词： γ辐照 辐照效应 光伏器件 碲镉汞     

量子点红外探测器的噪声表征

为了表征噪声对量子点红外探测器性能的影响, 本文推导了噪声的理论模型. 该模型通过考虑纳米尺度电子传输和微米尺度电子传输对激发能的共同影响, 并结合噪声增益, 实现了对噪声的估算. 得到的结果与实验的数据相比, 显示了很好的一致性, 从而验证了这个模型的正确性. 关键词： 电子传输 暗电流 增益 噪声     

基于表面等离激元的长波QWIP光栅优化

为了提高长波量子阱红外探测器的灵敏度及探测率,采用表面等离激元效应来提高量子阱红外探测器中二维光栅的耦合效率。利用三维时域有限差分算法,分析表面等离激元作用下,长波量子阱红外探测器中二维金属薄膜光栅参数对入射光的调制作用。计算结果表明,对于8 m的入射光,当光栅周期P=2.8 m,孔直径D=1.4 m,光栅层厚度L=0.04 m时,X Y平面内Z方向电场值最大,光栅的耦合效率最高。     

Study on the p-type QWIP-LED device

A p-type quantum well infrared photodetector (QWIP) integrated with a light-emitting diode (LED) (named QWIP-LED) was fabricated and studied. The infrared photo-response spectrum was obtained from the device resistance variation and the near-infrared photo-emission intensity variation. A good agreement between these two spectra was observed, which demonstrates that the long-wavelength infrared radiation around 7.5 μm has been transferred to the near-infrared light at 0.8 μm by the photo-electronic process in the QWIP-LED structure. Moreover, the experimentally observed infrared response wavelength is in good agreement with the theoretical calculation value of 7.7 μm. The results on the upconversion of the infrared radiation will be very useful for the new infrared focal plane array technology.     

Dark currents of GaAs/AlGaAs quantum-well infrared photodetectors

We study the dark current of the GaAs/AlGaAs quantum-well infrared photodetector (QWIP) by assuming a drift-diffusion carrier transport in the barriers where the electric fields are obtained by the current continuity condition and the self-consistent energy band structure. It has been shown that due to the current continuity condition, the dark currents across the QWIP devices are determined by the thermionic emission from the emitter to the multiple quantum well (MQW) region. The self-consistent calculation of the Schrödinger and Poisson equations shows a weak electric field in the barrier region connecting to the emitter (much smaller than the average field across the QWIP at low bias) due to the accumulation of carriers in the triangle quantum well formed at the emitter-MQW interface, which results in a very small dark current at low bias. The numerical results explain well our experimental observation.