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.     

Modelling of high-temperature dark current in multi-quantum well structures from MWIR to VLWIR

In this paper, a model to calculate the dark current of quantum well infrared photodetectors at high-temperature regime is presented. The model is derived from a positive-definite quantum probability-flux and considers thermionic emission and thermally-assisted tunnelling as mechanisms of dark current generation. Its main input data are the wave functions obtained by time-independent Schrodinger equation and it does not require empirical parameters related to the transport of carriers. By means of this model, the dark current of quantum well infrared photodetectors at high-temperature regime is investigated with respect to the temperature, the barrier width, the applied electric field and the position of the first excited state. The theoretical results are compared with experimental data obtained from lattice-matched InAlAs/InGaAs, InGaAsP/InP on InP substrate and AlGaAs/GaAs structures with rectangular wells and symmetric barriers, whose absorption peak wavelengths range from MWIR to VLWIR. The corresponding results are in a good agreement with experimental data at different temperatures and at a wide range of applied electric field.     

Comparative study between different quantum infrared photodetectors

This paper presents a theoretical analysis for the dark current characteristics of different quantum infrared photodetectors. These quantum photodetectors are quantum dot infrared photodetectors (QDIP), quantum wire infrared photodetectors (QRIP), and quantum well infrared photodetectors (QWIP). Mathematical models describing these devices are introduced. The developed models accounts for the self-consistent potential distribution. These models are taking the effect of donor charges on the spatial distribution of the electric potential in the active region. The developed model is used to investigate the behavior of dark current with different values of performance parameters such as applied voltage, number of quantum wire (QR) layers, QD layers, lateral characteristic size, doping quantum wire density and temperature. It explains strong sensitivity of dark current to the density of QDs/QRs 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. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among them are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors.     

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.     

Direct observation of the carrier transport process in InGaN quantum wells with a pn-junction

A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported.According to the well established light-to-electricity conversion theory,quantum wells(QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels,owing to quantum confinement,and cannot form a photocurrent.We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent,indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs.We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions.Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors.     

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.     

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.     

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.     

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 analysis of quantum wire infrared photodetectors under both dark and illumination conditions

This paper presents a theoretical analysis for the characteristics of quantum wire infrared photodetectors (QRIPs). Mathematical model describing this device is introduced. Maple 4 software is used to device this model. The developed model is used to investigate the behavior of the device with different values of performance parameters such as number of quantum wire layers, lateral characteristic size, and temperature. The modeling results are validated against experimental published work and full agreements are obtained. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among both quantum well infrared photodetectors (QWIPs) and QRIPs are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors (QDIPs).     

Nanostructures with Ge–Si quantum dots for infrared photodetectors

In this paper questions of optimization of growth conditions in the method of molecular beam epitaxy for creation of high-efficient quantum dot infrared photodetectors are considered. As a model material system for theoretical investigations, heterostructures with germanium-silicon quantum dots on the silicon surface are chosen. For calculations of the dependencies of quantum dots array parameters on synthesis conditions the kinetic model of growth of differently shaped quantum dots based on the general nucleation theory is proposed. The theory is improved by taking into account the change in free energy of nucleation of an island due to the formation of additional edges of islands and due to the dependence of surface energies of facets of quantum dots on the thickness of a 2D wetting layer during the Stranski–Krastanow growth. Calculations of noise and signal characteristics of infrared photodetectors based on heterostructures with quantum dots of germanium on silicon are done. Dark current in such structures caused by thermal emission and barrier tunneling of carriers, as well as detectivity of the photodetector in the approximation of limitation by generation-recombination noises are estimated. Moreover, the presence of dispersion of quantum dots by size is taken into account in the calculations of the generation-recombination noises. Results of calculations of the properties of structures with quantum dots and their dependencies on growth parameters, as well as the characteristics of quantum dot photodetectors are presented. Comparison of the estimated parameters of quantum dots ensembles and the characteristics of quantum dot photodetectors with experimental data is carried out.     

Arguments for p-type Si 1 − xGe x/Si quantum well photodetectors for the far- and very-far (terahertz)-infrared

An analysis, by a carrier scattering approach, of the thermionic emission contribution to the dark current is carried out in conventional bound-to-continuum quantum well infrared photodetectors (QWIPs). It is found that the thermionic emission increases with increasing temperature or when extending the detection wavelength from mid- to far-infrared. Considering p-type instead of n-type material, however, the increased effective mass decreases the thermionic emission. Designs for mid- and far-infrared p-type QWIPs based on the Si _1 − xGe _x/Si system are discussed for both normal and non-normal incident geometries.     

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.     

Quantum Dot Research: Current State and Future Prospects

This article reviews the current state of research involving semiconductor quantum dots, provides a brief review of the theory behind their unique properties, and an introduction explaining the importance of quantum dot research. The characteristic shifting of the band gap energy with quantum dot size, as predicted from the density of states for low-dimensional structures, allows experimental measurements to determine the extent to which quantum confinement effects play a role in the resulting properties. A few of the current techniques used to measure the presence and physical characteristics of quantum dots and their energy levels is reviewed, including transmission electron microscopy, optical transmission, and Raman and photoluminescence spectroscopy. Finally, some of the more exciting applications for quantum dots currently being researched for use in the field of optoelectronics are reviewed, including quantum dot infrared photodetectors, quantum dot lasers, and quantum dot solar cells. Comments are made on the current progress and the future prospects of quantum dot research and device applications.     

Tunneling current of the Coulomb-coupled quantum dots embedded in n-n junction

Taking account of the electron--electron (hole) and electron--hole interactions, the tunneling processes of the main quantum dot (QD) Coulomb-coupled with a second quantum dot embedded in n--n junction have been investigated. The eighteen resonance mechanisms involved in the tunneling processes of the system have been identified. It is found that the tunneling current depends sensitively on the electron occupation number in the second quantum dot. When the electron occupation number in the second dot is tiny, both the tunneling current peaks and the occupation number plateaus in the main QD are determined by the intra-resonance mechanism. The increase of the electron occupation number in the second dot makes the inter-resonance mechanism participate in the transport processes. The competition between the inter and intra resonance mechanisms persists until the electron occupation number in the second dot reaches around unity, leading to the consequence that the inter-resonance mechanisms completely dominate the tunneling processes.     

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     

Long wavelength infrared (LWIR) photodetection in a modulation doped thyristor

A modulation doped thyristor concept is described for LWIR photodetection based upon intersubband bound to continuum absorption. The intersubband absorption generates photocurrent from undoped quantum wells to modulation doped layers (MDL). Due to the lower dark current compared to conventional quantum well infrared photodetectors (QWIPs), the thyristor infrared detector operates with little or no cooling and with similar or better performance than QWIPs at low temperatures. The operating characteristics of absorption coefficient, quantum efficiency, responsivity, detectivity, infrared gain, and dark current are determined as a function of thyristor voltage and input power level in the range of 1 μW/cm².     

Selective optical doping to predict the performance and reveal the origin of photocurrent peaks in quantum dots-in-a-well infrared photodetectors

Resonant optical pumping across the band gap was used as artificial doping in InAs/In_0.15Ga_0.85As/GaAs quantum dots-in-a-well infrared photodetectors. Through efficient filling of the quantum dot energy levels by simultaneous optical pumping into the ground states and the excited states of the quantum dots, the response was increased by a factor of 10. Low temperature photocurrent peaks observed at 120 and 148 meV were identified as intersubband transitions emanating from the quantum dot ground state and the quantum dot excited state, respectively by a selective increase of the electron population in the different quantum dot energy levels.     

Photoconductivity of Ge/Si quantum dot photodetectors

Various structures of self-assembled Ge/Si quantum dot infrared photodetectors were implemented and investigated. The electronic structure of the QDIPs was studied by electrical and optical techniques including I–V characteristics, dark current, photoconductivity, photoluminescence, and photo-induced infrared absorption. The photoconductive spectra consist of a broad multi-peak, composed of peaks ranging from 70 to 220 meV. Their relative intensity changes with bias. Comparative dark current measurements were performed. Dark current limits the performance of this first generation of Ge/Si QDIPs. It is plausible that direct doping in the dot layer is a viable way of reducing the dark current.