量子点红外探测器的特性与研究进展

半导体材料红外探测器的研究一直吸引人们非常广泛的兴趣．以量子点作为有源区的红外探测器从理论上比传统量子阱红外探测器具有更大的优势．文章讨论了量子点红外探测器几个重要的优点，包括垂直入射光响应、高光电导增益、更低的暗电流、更高的响应率和探测率，等等．此外，报道了量子点红外探测器研究中一些最新的实验结果．在此基础上，分析了现存问题，并提出了进一步提高器件性能的几种可能途径．     

Characteristics and developments of quantum-dot infrared photodetectors

Quantum dots infrared photodetectors (QDIPs) theoretically have several advantages compared with quantum wells infrared photodetectors (QWIPs). In this paper, we discuss the theoretical advantages of QDIPs including the normal incidence response, lower dark current, higher responsivity and detectivity, etc. Recent device fabrication and experiment results in this field are also presented. Based on the analysis of existing problems, some approaches that would improve the capability of the device are pointed out.     

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.     

Electron transfer based voltage tunable two-color quantum-well infrared photodetectors

We present a detailed investigation of the temperature T dependence of photoresponse of voltage tunable two-color quantum-well infrared photodetectors (QWIPs) that are based on the transfer of electrons between coupled QWs under an applied bias V_b. For T40 K, the peak detection wavelength switches from 7.2 μm under positive bias to 8.6 μm under large negative bias as electrons are transferred from the right QW (RQW) to the left QW (LQW). For T50 K, the short wavelength peak is not only present for both bias polarities but also increases rapidly with T while the long wavelength peak decreases rapidly with T. We investigate this temperature dependence by extracting absorption coefficient and photoconductive gain g using corrugated QWIPs with different corrugation periods. The deduced absorption spectra indicate that the LQW population first increases and then decreases with increasing negative bias for T50 K. The deduced gain spectra show that short and long wavelength gain under negative bias exhibit a strong enhancement and reduction, respectively, with T above 50 K. We show that both these temperature dependences are caused by large thermal currents from the LQWs, which are designed for long wavelength detection and, therefore, have a significantly lower activation energy than the RQWs.     

An FDTD approach to the simulation of quantum-well infrared photodetectors

A Finite Difference Time Domain approach is used to design and to optimize quantum-well based infrared photodetectors. Results showing the influence of some parameters on the performance of these devices are presented and discussed.     

Physics of non-adiabatic transport and field-domain effect in quantum-well infrared photodetectors

A previous theory for studying the distribution of non-uniform fields in multiple-quantum-well photodetectors under an ac voltage is generalized by including non-adiabatic space-charge-field effects. Numerical calculations indicate that field-domain effects are only important at high temperatures or high voltages when both injection and sequential-tunneling currents are significant. On the other hand, it is found that the non-adiabatic effects included in this generalized theory become significant at low temperatures and low voltages when field-domain effects are negligible. In order to explain the non-adiabatic charge-density fluctuations quantum-statistically, a non-adiabatic differential equation is derived based on the self-consistent Hartree model by using a shifted Fermi–Dirac model for the local fluctuation of electron distributions. The non-adiabatic effect is found to cause an “equilibrium” state variation with time under an ac voltage.     

Comparison studies of infrared photodetectors with a quantum-dot and a quantum-wire base

This paper mainly presents a theoretical analysis for the characteristics of quantum dot infrared photodetectors (QDIPs) and quantum wire infrared photodetectors (QRIPs). The paper introduces a unique mathematical model of solving Poisson’s equations with the usage of Lambert W functions for infrared detectors’ structures based on quantum effects. Even though QRIPs and QDIPs have been the subject of extensive researches and development during the past decade, it is still essential to implement theoretical models allowing to estimate the ultimate performance of those detectors such as photocurrent and its figure-of-merit detectivity vs. various parameter conditions such as applied voltage, number of quantum wire layers, quantum dot layers, lateral characteristic size, doping density, operation temperature, and structural parameters of the quantum dots (QDs), and quantum wires (QRs). A comparison is made between the computed results of the implemented models and fine agreements are observed. It is concluded from the obtained results that the total detectivity of QDIPs can be significantly lower than that in the QRIPs and main features of the QRIPs such as large gap between the induced photocurrent and dark current of QRIP which allows for overcoming the problems in the QDIPs. This confirms what is evaluated before in the literature. It is evident that by increasing the QD/QR absorption volume in QDIPs/QRIPs as well as by separating the dark current and photocurrents, the specific detectivity can be improved and consequently the devices can operate at higher temperatures. It is an interesting result and it may be benefit to the development of QDIP and QRIP for infrared sensing applications.     

Optoelectronic characteristics of CdTe/HgTe/CdTe quantum-dot quantum-well nanoparticles

Optoelectronic characteristics of CdTe/HgTe/CdTe quantum-dot quantum-well (QDQW) nanoparticles synthesized by the colloidal method are investigated in this study. Strong exciton bands were observed in absorption and photoluminescence (PL) spectra taken for the CdTe/HgTe/CdTe QDQW nanoparticles. The energy difference between the exciton absorption and PL bands is larger than those obtained with CdTe and HgTe nanoparticles. Photocurrent-voltage curves and time-dependent photocurrent curves were obtained for the CdTe/HgTe/CdTe QDQW nanoparticles. With regard to the photocurrent mechanism of these QDQW nanoparticles, those charge carriers participating in the formation of excitons may not contribute to the photocurrent, because of the large binding energy of the excitons. Moreover, it is suggested in this paper that free holes in the HgTe quantum-well in the valance band, rather than free electrons, are the main contributors to the photocurrent.     

The theory of multiple quantum-well GaAs-AlGaAs infrared detectors

The theory of multiple quantum-well GaAs-AlGaAs IR detectors based on the principle of quantum well photoionization is presented. The expression for the photoionization probability of the symmetric quantum-well is found to be exact in the effective mass approximation. Depolarization effects in the optical absorption spectra are discussed. We demonstrate that the depolarization shift of the spectrum maximum and its broadening lead to non-monotonic dependence of the photodetector detectivity on the electron concentration in wells in the background limited IR performance condition. The optimal factor of quantum-well filling, corresponding to the maximum of detectivity is rather small, and for the photoresistor with boundary wavelength λ₁ = 10 μm, is θ =0.10.We have also performed calculations for the concentration dependence of the transition temperature for background limited IR performance and found that for optimal concentrations it is about T = 83 K (for λ₁ = 10 μm). The lifetime of non-equilibrium electrons is determined by capturing processes into the wells accompanied by emission of polar optical phonons and is τ ≅ 2 × 10⁻¹¹ s. The gain, along with the photoresistor sensitivity, is maximal for structures with a single quantum well.     

Photon parameter characterization of infrared photodetectors

An alternative formulation of IR photodetector theory in photon parameter terms is examined and it is shown that within such a formulation, subsystem figures-of-merit such as SNR and NETD may be separated entirely into factors describing respectively the system geometry, noise bandwidth, signal-to-background contrast, atmospheric transmission, background-to-noise ratio and detector linearity. For the evaluation of signal current, a dimensionless photon responsivity is introduced, analogous to the standard current responsivity. A special feature is the specification of the IR background current as an inherent part of the formalism. In this respect, r.m.s. noise currents may be determined from values of an alternative specific quantity, the specific background-to-noise ratio B¹, that is used in place of the standard specific detectivity D¹. Simple relationships are derived for conversion between responsivity and photon responsivity, and between the standard detectivity D¹ and B¹.     

近红外光电探测器的发展与应用

近红外光电探测器在军事和国民经济中应用广泛,如航空航天、光通信、工业控制、近红外成像等领域。文章首先讲述了近红外光电探测器的发展历史、工作原理和基本应用情况。通过比较各类光电探测器的性能参数,可以看出基于纳米材料的近红外光电探测器具有很高的响应度、探测率和响应速度。然后,文章将着重介绍近红外光电探测器在光纤通信、无人驾驶、模式识别和光电耦合等领域的发展情况及相关原理。最后,文章对近红外光电探测器的发展前景进行了展望。未来近红外光电探测器将全面应用于各大领域,但是高端的材料生长技术、高效的光电转化方法以及大规模光电器件集成工艺等方面的不足依旧是限制纳米光电探测器发展的主要因素。     

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.     

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     

Ground state of excitons in quantum-dot quantum-well nanoparticles： stochastic variational method

Within the framework of effective mass approximation, the ground state of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles is solved by using the stochastic variational method, in which the finite band offset and the heavy (light) hole exciton states are considered. The calculated 1s_e－1s_h transition energies for the chosen CdS/HgS/CdS QDQW samples are in good agreement with the experimental measurements. Moreover, some previous theoretical results are improved.     

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.     

Designs of broadband quantum-well infrared photodetectors and 8–12 μm test device results

Several designs of broadband quantum-well infrared photodetectors are considered. The performance characteristics are analyzed by modeling. Test devices designed to cover the 8–12 μm wavelength region are fabricated and characterized. The results show that a broad device can be realized and their performance is in accordance with expectation.     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置. 关键词： 太赫兹量子阱探测器 太赫兹量子级联激光器 太赫兹通信 Fourier变换红外光谱     

基于太赫兹量子阱探测器的太赫兹量子级联激光器发射谱研究

采用一个光谱匹配的太赫兹(THz)量子阱探测器(QWP)研究了一激射频率约为41 THz的THz量子级联激光器(QCL)在不同驱动电流下的发射谱,分析了测量得到的发射谱谱型和谱峰位置,根据测量的发射谱估算了太赫兹量子级联激光器发射功率随驱动电流变化的情况,从而得到了THz QCL激射的电流密度范围及其阈值电流密度.文中还研究了THz QWP在不同温度下对THz QCL 激光辐射的响应特性.研究结果表明,THz QWP在表征THz QCL的发射谱方面是一种很好的探测器,并有望成为未来THz通信中的接收装置.