Quantum mechanical scattering investigation of the dark current in quantum well infrared photodetectors (QWIPs)

This work focuses on the quantum mechanical evaluation of two components of the dark current in quantum well infrared photodetectors (QWIPs)––field induced emission (FIE) and thermionic emission (TE). The negligible value of the third component of the dark current––sequential tunnelling (ST)––was shown theoretically in previously published work. Calculations are on devices that cover the long wavelength- to very long wavelength-infrared (LWIR to VLWIR) region of the spectrum. The results prove theoretically for the first time various experimentally observed characteristics of these two emission components of the dark current.     

Performance improvement of quantum dot infrared photodetectors through modeling

This paper presents a method to evaluate and improve the performance of quantum dot infrared photodetectors (QDIPs). We proposed a device model for QDIPs. The developed model accounts for the self-consistent potential distribution, features of the electron capture and transport in realistic QDIPs in dark and illumination conditions. This model taking the effect of donor charges on the spatial distribution of the electric potential in the QDIP active region. The model is used for the calculation of the dark current, photocurrent and detectivity as a function of the structural parameters such as applied voltage, doping QD density, QD layers, and temperature. It explains strong sensitivity of dark current to the density of QDs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Results show the effectiveness of methodology introduced.     

Physical model for the dark current of quantum dot infrared photodetectors

Dark current has attracted much attention in recent years due to its great influence on the performance of the QDIP. In this paper, a model for the dark current is proposed with the consideration of the influence of the nanoscale electron transport on the dark current based on the dark current model proposed by H.C. Liu. The model permits calculating the dark current as a function of the electric field, and it can further estimate the photocurrent, the current responsivity and the detectivity via the current equilibrium equation under the dark condition. The results obtained show a good agreement with the experimental results and manifest the validity of the proposed model.     

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     

甚长波量子阱红外探测器的暗电流特性研究

基于载流子在量子结构中的输运理论研究了甚长波量子阱红外探测器(峰值响应波长15μm，量子阱个数大于40)的载流子的输运性质.研究结果表明，在甚长波量子阱红外探测器中，电流密度一般很低，暗电流主要来源于能量高于势垒边的热激发电子.通过薛定谔方程和泊松方程以及电流的连续性方程的自洽求解，发现外加偏压下电子浓度在甚长波器件各量子阱的分布发生较大变化，电场在整个器件结构上呈非均匀分布，靠近发射极层的势垒承担的电压远远高于均匀分布的情形.平带模型假定电压在器件体系上均匀分布，导致小偏压下的理论计算值远远低于实验值. 关键词： 甚长波量子阱红外探测器 量子波输运 暗电流     

Multi-color tunneling quantum dot infrared photodetectors operating at room temperature

Quantum dot structures designed for multi-color infrared detection and high temperature (or room temperature) operation are demonstrated. A novel approach, tunneling quantum dot (T-QD), was successfully demonstrated with a detector that can be operated at room temperature due to the reduction of the dark current by blocking barriers incorporated into the structure. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers placed in the structure. A two-color tunneling-quantum dot infrared photodetector (T-QDIP) with photoresponse peaks at 6 μm and 17 μm operating at room temperature will be discussed. Furthermore, the idea can be used to develop terahertz T-QD detectors operating at high temperatures. Successful results obtained for a T-QDIP designed for THz operations are presented. Another approach, bi-layer quantum dot, uses two layers of InAs quantum dots (QDs) with different sizes separated by a thin GaAs layer. The detector response was observed at three distinct wavelengths in short-, mid-, and far-infrared regions (5.6, 8.0, and 23.0 μm). Based on theoretical calculations, photoluminescence and infrared spectral measurements, the 5.6 and 23.0 μm peaks are connected to the states in smaller QDs in the structure. The narrow peaks emphasize the uniform size distribution of QDs grown by molecular beam epitaxy. These detectors can be employed in numerous applications such as environmental monitoring, spectroscopy, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.     

Review of current progress in quantum dot infrared photodetectors

Quantum dot infrared photodetectors (QDIPs) have made significant progress after their early demonstration about a decade ago. We review the progress made by QDIP technology over the last few years and compare QDIPs with quantum well infrared photodetectors (QWIPs). It is shown that the performance of QDIPs has significantly improved using novel architectures such as dots‐in‐a‐well designs, and large‐format (1 K × 1 K) focal plane arrays have been realized. However, even though there are significant reports of performance parameters better than QWIPs from single‐pixel devices, QDIP‐based focal plane arrays are still a factor of 3–5 worse in terms of noise equivalent temperature difference. We discuss the reasons for the performance gap and the key scientific and technological challenges that need to be addressed to achieve the full potential of QD‐based technology.     

Performance investigations of quantum dot infrared photodetectors

Quantum dot infrared photodetectors (QDIPs) have already attracted more and more attention in recent years due to a high photoconductive gain, a low dark current and an increased operating temperature. In the paper, a device model for the QDIP is proposed. It is assumed that the total electron transport and the self-consistent potential distribution under the dark conditions determine the dark current calculation of QDIP devices in this model. The model can be used for calculating the dark current, the photocurrent and the detectivity of QDIP devices, and these calculated results show a good agreement with the published results, which illustrate the validity of the device model.     

Temperature dependent responsivity of quantum dot infrared photodetectors

Temperature dependent behavior of the responsivity of InAs/GaAs quantum dot infrared photodetectors was investigated with detailed measurement of the current gain. The current gain varied about two orders of magnitude with 100 K temperature change. Meanwhile, the change in quantum efficiency is within a factor of 10. The dramatic change of the current gain is explained by the repulsive coulomb potential of the extra carriers in the QDs. With the measured current gain, the extra carrier number in QDs was calculated. More than one electron per QD could be captured as the dark current increases at 150 K. The extra electrons in the QDs elevated the Fermi level and changed the quantum efficiency of the QDIPs. The temperature dependence of the responsivity was qualitatively explained with the extra electrons.     

Detectivity dependence of quantum dot infrared photodetectors on temperature

The detectivity of Quantum dot infrared photodetectors (QDIPs) has always attracted a lot attention as a very important performance parameter. In the paper, based on the theoretical model for the detectivity with the consideration of the common influence of the microscale electron transport, the nanoscale electron transport and the self-consistent potential distribution of the electrons, the dependence of the detectivity of the QDIP on temperature is discussed by analyzing the influence of the temperature on the average electrons number in a quantum dot. Specifically, the average electrons number in a quantum dot shows different change trends (from the increase to decrease) with the increase of the temperature, but the detectivity presents the single decrease trend with the temperature, which can provide the designers with the theoretical guidance for the performance optimization of the QDIP devices.     

High responsivity, LWIR dots-in-a-well quantum dot infrared photodetectors

In this paper we report studies on normal incidence, InAs/In_0.15Ga_0.85As quantum dot infrared photodetectors (QDIPs) in the dots-in-a-well (DWELL) configuration. Three QDIP structures with similar dot and well dimensions were grown and devices were fabricated from each wafer. Of the three devices studied, the first served as the control, the second was grown with an additional 400 Å AlGaAs blocking layer, and the third was grown on a GaAs n+ substrate with the intention of testing a single pass geometry. Spectral measurements on all three devices show one main peak in the long-wave IR (≈8 μm). The absorption was attributed to the bound-to-bound transition between the ground state of the InAs quantum dot and the ground state of the In_0.15Ga_0.85As well. Calibrated peak responsivity and peak detectivity measurements were performed on each device at 40, 60, and 80 K. For the same temperatures, frequency response measurements from 20 Hz to 4 kHz at a bias of V_b=−1 V were also performed. The addition of the blocking layer was shown to slightly enhance responsivity, which peaked at 2.4 A/W at 77 K, V_b=−1 V and responsivity was observed to be significantly reduced in the single pass (n+ substrate) sample. The rolloff of the frequency response was observed to be heavily dependent on temperature, bias, and irradiance. The results from the characterization of each sample are reported and discussed.     

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.     

Detailed characterization of a systematic set of quantum dot infrared photodetectors

The results of a detailed characterization study on a systematic set of InAs/GaAs self-assembled quantum dot infrared photodetectors are presented. A simple physical picture is also discussed to account for the main observed features. Photoresponse characteristics in a wide spectral region from the mid- to far-infrared are reported. Clear polarization behaviors with a dominant P-polarized response in the mid-infrared and a strong S-response in the far-infrared regions are shown. These behaviors can be qualitatively understood in view of the quantum dot shape of a large in-plane diameter and a small height in the growth direction. With a set of three samples, effects of the number of electrons per quantum dot on the spectra are investigated.     

微波作用下有直接隧穿量子点系统中的泵流特性

利用演化算符的方法,研究了量子点体系中的电流以及自旋流,该体系中量子点和左右磁性电极耦合并且受到微波作用,且两电极之间有直接隧穿,得到了体系电流的解析表达式.发现对于无直接隧穿和零偏压情况,无论对称结构还是非对称结构,电流和自旋流总为零.对于直接隧穿和零偏压情况,对于两边为非对称结构,微波场辐射在量子点上可以导致自旋流而非零的总电流,给出了平行和反平行磁构型下的结果并进行了讨论;对于两边为对称结构结构,平行磁构型下,量子点上加微波场时自旋流和总电流均为零;在反平行磁构型下,量子点上加微波场可以导致自旋流而 关键词： 微波场 直接隧穿 量子点 泵流     

The role of sequential tunnelling in the dark current of quantum well infrared photodetectors (QWIPs)

A quantum mechanical approach is taken to investigate the contribution of sequential tunnelling as a component of the dark current in quantum well infrared photodetectors (QWIPs). Calculations are performed on three different experimentally reported QWIP devices made for different detection wavelengths. The results show that the sequential tunnelling component remains rather constant with different devices, however it is swamped by the thermionic emission components of the dark current at longer wavelengths. The lack of a local maximum in the dark current due to resonant LO phonon emission, which should be observed at short wavelengths, suggests that interface roughness and alloy disorder could be destroying the coherence of the electron wavefunctions between quantum wells.     

InAs/GaAs quantum dot infrared photodetectors with different growth temperatures

InAs/GaAs quantum dot infrared photodetectors were fabricated with quantum dots grown at three different temperatures. Large detection wavelength shift (5–14.5 μm) was demonstrated by changing 40 degrees of the epitaxy temperature. The smaller quantum dots grown at lower temperature generate 14.5 μm responses. The detectivity of the normal incident 15 μm QDIP at 77 K is 3 × 10⁸ cm Hz^1/2/W. A three-color detector was also demonstrated with quantum dots grown at medium temperature. The three-color detection comes from two groups of different sizes of dots within one QD layer. This new type of multicolor detector shows unique temperature tuning behavior that was never reported before.     

Spin current in double quantum dot

We have studied the dynamical behaviours of two electrons confined in a double quantum dot driven by rotating magnetic fields in terms of the theory of Lewis－Riesenfeld Hermitian invariants for the explicitly time-dependent Hamiltonian. The coherent spin oscillations in the dot provide a generation source for spin current. Exact solutions obtained allow us to investigate the dynamical properties of the spin localization for various initial localized states.     

Band structure and impurity effects on optical properties of quantum well and quantum dot infrared photodetectors

We examined theoretically band structure and discrete dopant effects in the quantum well infrared photodetector (QWIP) and the quantum dot infrared photodetector (QDIP). We find that in QWIPs discrete dopant effects can induce long wavelength infrared absorption through impurity assisted intra-subband optical transitions. In QDIPs, we find that a strategically placed dopant atom in a quantum dot can easily destroy the symmetry and modify the selection rule. This mechanism could be partially responsible for normal incidence absorption observed in low-aspect-ratio quantum dots.