Search

Herein, a model is developed to study the polarization‐selective light‐coupling in quantum well infrared photodetector arrays with 15 and 30 μm pixel pitch. The polarization‐selective light‐coupling is achieved using 1D lamella gratings with varying grating orientation and studied through 2D and 3D finite‐element method simulations. The extracted absorption quantum efficiency ηabs, derived from the field distribution, shows excellent agreement with experimental data in terms of absorption peak position for both pitch sizes. Several factors impacting the simulated absorptance level are discussed and a good agreement between the simulation and measured ηabs is achieved. Thanks to the developed 3D model, the polarization‐selective light‐coupling in pixels with 0° and 45° grating orientation is explored. The developed model paves the way for future studies on enhanced light‐coupling in small pitch infrared detectors using resonance structures. [ABSTRACT FROM AUTHOR]

During infrared detection, the thermal radiation from the background generates substantial photon noise and thus severely limit the capability of an infrared detector to identify a target. Going beyond this limitation has been a long‐standing challenge in the development of infrared detectors. This paper proposes to break this limitation by creating a narrow photoresponse band with a high peak responsivity to reject the background radiation and enhance the responsivity to the target with characteristic emission lines. This scheme is numerically demonstrated in a dimerized grating integrated quantum well infrared photodetector, based on critical coupling with a Brillouin zone folding induced quasi‐bound state in the continuum (BIC). The asymmetric deformation of the grating structure folds the photonic band and generates a quasi‐BIC with a tunable high radiation Q factor (QR) at the Γ point. By reducing the doping concentration of the quantum wells for a high absorption Q factor (QA) and tuning the QR to make QR = QA for critical coupling, a narrowband photoresponse with a high peak responsivity is achieved and the background‐limited specific detectivity of 4.55 × 1012 cm Hz1/2 W−1 is obtained for a 2π field of view, surpassing the ideal‐photoconductor limit by 92 times. [ABSTRACT FROM AUTHOR]

Introduction. Quantum well infrared photodetectors (QWIP) are characterized by a wide application range. A large market demand for such photodetectors determines the importance of elucidating the principle of their operation.Aim. To carry out a research study into the influence of the AlGaAs potential barrier surrounding GaAs quantum wells on the QWIP operating bias voltage in the long-wavelength region of the spectrum (8…10 μm).Materials and methods. QWIP experimental samples were manufactured based on the GaAs/AlGaAs semiconductor material system using molecular beam epitaxy. The photosensitive (active) region of the structures contained 50 GaAs quantum wells with a thickness of 50 Å thick separated by AlGaAs barriers. Quantum wells were doped in situ with silicon as a donor impurity. The wavelength of the maximum spectral sensitivity of all samples ranged within 8…9 μm. The barrier width was the variable parameter. After passing the planar modification process route, the current–voltage characteristics were measured in all structures.Results. Reduction in the barrier thickness is capable of shifting the peak of photosensitivity towards the region of lower bias voltages with a slight increase in the dark current values.Conclusion. The study of the influence of the applied bias voltage presents both scientific and practical interest. On the one hand, the results improve the current understanding of the behavior of the dark current in QWIP. On the other, they provide the possibility of managing the maximum current sensitivity, shifting it towards the region of the required operating voltages of the multiplexers.

We present an integrated device combining a double L-shaped chiral metasurface with long-wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs), achieving a circular polarized extinction ratio (CPER) as high as 45 in the long-wavelength infrared range of 7–9 μm. The unit of the chiral metasurface array consists of two structurally identical L-shaped gold structures with central symmetry. The CPER of the double L-shaped QWIPs is 14 times higher than that of a single L-shaped QWIP. The device operates in three modes within the detection band: the microcavity mode, the surface plasmon polariton (SPP) mode, and the hybrid mode. The double L-shaped chiral structure selects and reflects a small portion of left-handed circularly polarized light (LCP), while the majority enters the device and excites SPP modes with the bottom gold grating layer, leading to an absorption enhancement. In contrast, right-handed circularly polarized light (RCP) is mostly reflected with limited excitation of SPP waves. QWIPs exhibit a peak absorption of 0.8 and a coupling efficiency of 2700% in the active region of the quantum well due to the combined effects of the microcavity and SPP modes, in which the SPP mode plays a dominant role. The proposed device maintains high circular polarization discrimination capability under large incident angles and can be applied in spectral imaging. [ABSTRACT FROM AUTHOR]

We present an integrated device combining a double L-shaped chiral metasurface with long-wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs), achieving a circular polarized extinction ratio (CPER) as high as 45 in the long-wavelength infrared range of 7–9 μm. The unit of the chiral metasurface array consists of two structurally identical L-shaped gold structures with central symmetry. The CPER of the double L-shaped QWIPs is 14 times higher than that of a single L-shaped QWIP. The device operates in three modes within the detection band: the microcavity mode, the surface plasmon polariton (SPP) mode, and the hybrid mode. The double L-shaped chiral structure selects and reflects a small portion of left-handed circularly polarized light (LCP), while the majority enters the device and excites SPP modes with the bottom gold grating layer, leading to an absorption enhancement. In contrast, right-handed circularly polarized light (RCP) is mostly reflected with limited excitation of SPP waves. QWIPs exhibit a peak absorption of 0.8 and a coupling efficiency of 2700% in the active region of the quantum well due to the combined effects of the microcavity and SPP modes, in which the SPP mode plays a dominant role. The proposed device maintains high circular polarization discrimination capability under large incident angles and can be applied in spectral imaging.

• Achieving narrowband high-peak photoresponse by light coupling manipulation with a BZF quasi-BIC. • Far exceeding the ideal-photoconductor limit of D BLIP ∗ by the joint effect of a BZF quasi-BIC and critical coupling. • Tuning the peak wavelength over the LWIR range on the same chip. Quasi-bound states in the continuum (quasi-BIC) have tunable high Q factors and thus have many potential applications in optoelectronics. Here, we propose to construct a quasi-BIC with a perturbated elliptical-cylinder photonic crystal slab, and then develop a new way based on the quasi-BIC to address the background noise problem of infrared detectors. By integrating the photonic crystal slab with a quantum well infrared photodetector (QWIP), and by pushing the quasi-BIC system with absorption to the critical coupling state, an ultra-narrow photoresponse band (Q factor equal to 1150) with a high peak quantum efficiency (over 60%) is achieved in the long-wavelength infrared range. The critical coupling state is realized by matching the radiation Q factor, which is mainly controlled by the quasi-BIC, to the absorption Q factor, which is mainly controlled by the doping of the quantum wells (QWs). This device rejects most background radiation and thus significantly suppresses the background noise, resulting in a background limited specific detectivity (D BLIP ∗) 11.85 times that of a conventional ideal photoconductor. A detailed formula is employed for calculation of D BLIP ∗ , incorporating the wavelength and incident angle dependence of the quantum efficiency. The ultra-narrow photoresponse band with a high peak responsivity can be tuned over the photosensitive wavelength range of the QWs by simply modifying the in-plane structural parameters. This work opens a new avenue to greatly enhance the specific detectivity for infrared detectors based on the joint effect of quasi-BIC and critical coupling. [ABSTRACT FROM AUTHOR]

We propose a stacked dual-band quantum well infrared photodetector (QWIP) integrated with a double-layer gold disk. Two 10-period quantum wells (QW) operating at different wavelengths are stacked together, and gold nano-disks are integrated on their respective surfaces. Numerical calculations by finite difference time domain (FDTD) showed that the best enhancement can be achieved at 13.2 and 11.0 µm. By integrating two metal disks, two plasmon microcavity structures can be formed with the substrate to excite localized surface plasmons (LSP) so that the vertically incident infrared light can be converted into electric field components perpendicular to the growth direction of the quantum well (EZ). The EZ electric field component can be enhanced up to 20 times compared to the incident light, and it is four times that of the traditional two-dimensional hole array (2DHA) grating. We calculated the enhancement factor and coupling efficiency of the device in the active region of the quantum well. The enhancement factor of the active region of the quantum well on the top layer remains above 25 at the wavelength of 13.2 μm, and the enhancement factor can reach a maximum of 45. Under this condition, the coupling efficiency of the device reaches 2800%. At the wavelength of 11.0 μm, the enhancement factor of the active region of the quantum well at the bottom is maintained above 6, and the maximum can reach about 16, and the coupling efficiency of the device reaches 800%. We also optimized the structural parameters and explored the influence of structural changes on the coupling efficiency. When the radius (r1, r2) of the two metal disks increases, the maximum coupling efficiency will be red-shifted as the wavelength increases. The double-layer gold disk structure we designed greatly enhances the infrared coupling of the two quantum well layers working at different wavelengths in the dual-band quantum well infrared photodetector. The structure we designed can be used in stacked dual-band quantum well infrared photodetectors, and the active regions of quantum wells working at two wavelengths can enhance the photoelectric coupling, and the enhancement effect is significant. Compared with the traditional optical coupling structure, the structure we proposed is simpler in process and has a more significant enhancement effect, which can meet the requirements of working in complex environments such as firefighting, night vision, and medical treatment.

Highlights • Unusually high quantum efficiency in QWIPs with high In mole fraction InGaAs quantum wells. • Higher ability of normal-incident radiation absorption in high-x In x Ga 1−x As quantum wells. • Grating-free MWIR QWIPs with high-x In x Ga 1−x As quantum wells exhibit good sensitivity. Abstract Quantum well infrared photodetector (QWIP) technology is still the only thermal imaging sensor technology providing excellent pixel operability, uniformity and stability together with low production cost and insignificant 1/f noise. The main bottleneck of the standard QWIP technology is the low quantum efficiency and device gain inhibiting the utilization of the sensor for low background and/or high frame rate applications. This manuscript reports unusually high quantum efficiency observed in mid-wavelength infrared (MWIR) QWIPs constructed with solid-source molecular beam epitaxy grown thirty In 0.83 Ga 0.17 As quantum wells sandwiched between InP and GaInP barriers. Large area (300 × 300 μm2) bound-to-continuum detectors with ∼5.7 μm cut-off wavelength exhibited very broad (Δλ/λ p = ∼40%) responsivity spectrum together with impressively high peak absorption quantum efficiency of ∼20% and a 78 K peak specific detectivity above 1 × 1011 cmHz 1/2/W with f/2 optics in the absence of diffraction grating. Even higher signal-to-noise ratio was observed in grating-free small area (∼20 × 20 µm2) detectors hybridized to a fan-out substrate. Considering the expected improvements in the quantum efficiency by confining the responsivity spectrum to the narrower (and useful) wavelength region in the MWIR band and utilization of diffraction grating, the results presented in this manuscript have considerable potential to open the door to reshape the QWIP technology. [ABSTRACT FROM AUTHOR]

The characteristics of quantum well infrared photodetectors (QWIPs) which utilizing electromagnetically induced transparency (EIT) have been presented in this communication. Instead of direct absorption and creation of photoelectrons by the long wavelength infrared signal, the absorption properties of a short wavelength probe is modified by the infrared signal which subsequently creates photoelectrons. Owing to the indirect creation of photocurrent, the component of dark current which is due to thermionic emission is eliminated, thereby decreasing total dark current appreciably. The value of photocurrent depends on infrared signal power, bias voltage, probe detuning, and Rabi frequency of the control field. Results of this investigation may find potential applications in the development of terahertz infrared quantum well photodetectors under room temperature operation. • Characteristics of quantum well infrared photodetectors have been investigated. • The photodetectors utilize electromagnetically induced transparency. • Photoelectrons are created indirectly using the absorption of a probe field. • Indirect creation of photocurrent appreciably reduces dark current. • Rabi frequency of a control field and probe detuning govern photocurrent. [ABSTRACT FROM AUTHOR]

We present an equivalent circuit model for AlGaAs/GaAs long wavelength quantum well infrared photodetectors (LW-QWIPs). Bias dependence of the dark current and photoresponse is described with the aid of analogue circuit modeling technique in the TINA software. This model can be integrated with the readout circuit for the whole device circuit simulation and optimization further. The designed parameters of the LW-QWIPs can be fed into this model as user-defined circuit parameters to simulate the detector performance. The obtained results are consistent with the experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: We report the pixel and large format FPA level characteristics of strained InP/In0.48Ga0.52As QWIPs to demonstrate the advantages of this material system for LWIR thermal imaging. The grating coupled FPA pixels with responsivity peak and cut-off wavelengths of 8.5 and 9μm exhibited a peak quantum efficiency as large as 20% which has allowed desirable FPA operation at a temperature as high as 78K. InP/InGaAs QWIPs, when compared with those constructed with the AlGaAs/GaAs material system, offer the advantage of bias-adjustable gain (in a wide range) as well as higher quantum efficiency resulting in conversion efficiencies significantly higher than those provided by GaAs based QWIPs. These advantages show potential to overcome the limitations of the standard QWIP under high frame rate and/or low background conditions. [Copyright &y& Elsevier]

Abstract: Quantum well infrared photodetector (QWIP) technology has allowed the realization of low cost staring focal plane arrays (FPAs). However, AlGaAs/(In)GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate and/or low background conditions. We extensively discuss the effect of sensor gain on the FPA performance under various operating conditions, and highlight the superiority of the InP/InGaAs material system with respect to AlGaAs/GaAs for high speed/low background thermal imaging applications. InP/InGaAs QWIPs, providing a bias adjustable gain in a wide range, offer the flexibility of adapting the FPA to strict operating conditions. We also present an experimental comparison of large format AlGaAs/GaAs and (strained) InP/InGaAs QWIP FPAs under different operating conditions. A 640×512 QWIP FPA constructed with the 40-well strained InP/In0.48Ga0.52As material system displays a cut-off wavelength of 9.7μm (λp =8.9μm) with a BLIP temperature higher than 65K (f/2), and a peak quantum efficiency as high as 12% with a broad spectral response (Δλ/λp =17%). The conversion efficiency of the FPA pixels is as high as 20% under large bias (4V) where the detectivity is reasonably high (∼3×1010 cmHz1/2/W, f/2, 65K). While providing a considerably higher quantum efficiency than the pixels of a similar AlGaAs/GaAs FPA, the InP/InGaAs QWIP provides similar NETD values with much shorter integration times and, being less sensitive to the read noise, successfully operates with sub-millisecond integration times. The results clearly demonstrate that InP based material systems display high potential for single- and dual-band QWIP FPAs by overcoming the limitations of the standard GaAs based QWIPs under high frame rate and/or low background conditions. [Copyright &y& Elsevier]

Abstract: Our interest is to model the electronic transport in Quantum Well Infrared Photodetectors (QWIPs). Standard modelling was based on self-consistent calculation of the non-uniform electric field with empirical description of the electron capture (Thibaudeau et al., 1996 ). Realistic empirical parameters had to be extracted from experiment, consequently purely numerical studies were not possible. Moreover, this approach allowed only a qualitative description of transport phenomena. In order to get rid of adjustable parameters, we have changed for a modelling based on the microscopic description of the transport (Jovanović et al., 2004 ). We have applied this modelling to the design of a variety of QWIPs. For example, excellent agreement with experimental dark current–voltage curves for different sizes of the barriers is demonstrated on a 8μm detector over more than 6 orders of magnitude. The behaviour with respect to temperature on a wide range (30–200K) is also well reproduced on this device as well as on a 17μm detector. Those promising results confirm that this approach can give not only a good quantitative agreement but can also be a useful predictive tool. [Copyright &y& Elsevier]

Abstract: Quantum Well Infrared Photodetector (QWIP) usually suffer from a too moderate quantum efficiency and too large dark current which is often announced as crippling for low flux applications. Despite this reputation we demonstrate the ability of QWIP for the low infrared photon flux detection. We present the characterization of a state of the art 14.5μm QWIP from Alcatel-Thales III–V Lab. We developed a predictive model of the performance of an infrared instrument for a given application. The considered scene is a cryogenic wind tunnel (ETW), where a specific Si:Ga camera is currently used. Using this simulation tool we demonstrate the QWIP ability to image a low temperature scene in this scenario. QWIP detector is able to operate at 30K with a NETD as low as 130 mK. In comparison to the current detector, the operating temperature is 20K higher. The use of a QWIP based camera would allow a huge simplification of the optical part. [ABSTRACT FROM AUTHOR]

Abstract: Alternative material systems on InP substrate provide certain advantages for mid-wavelength infrared (MWIR), long-wavelength infrared (LWIR) and dual band MWIR/LWIR quantum well infrared photodetector (QWIP) focal plane arrays (FPAs). While InP/InGaAs and InP/InGaAsP LWIR QWIPs provide much higher responsivity when compared to the AlGaAs/GaAs QWIPs, AlInAs/InGaAs system facilitates completely lattice matched single band MWIR and dual band MWIR/LWIR FPAs. We present an extensive review of the studies on InP based single and dual band QWIPs. While reviewing the characteristics of InP/InGaAs and InP/InGaAsP LWIR QWIPs at large format FPA level, we experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ∼5.0μm with a QW width of 22Å in which case very broad spectral response (Δλ/λ p =∼30%) and a reasonably high peak detectivity are achievable leading to a noise equivalent temperature difference as low as 14mK (f/2) with 25μm pitch in a 640×512FPA. We also present the characteristics of InP based two-stack QWIPs with wavelengths properly tuned in the MWIR and LWIR bands for dual color detection. The results clearly demonstrate that InP based material systems display high potential for dual band MWIR/LWIR QWIP FPAs needed by third generation thermal imagers. [Copyright &y& Elsevier]

Abstract: Type II strained layer superlattice (SLS) has been making tremendous progress in the past few years funded by the Missile Defense Agency Advanced Technology Directorate (MDA/DV) under the Passive EO/IR Program. SLS has shown great potential as a future solution for infrared military systems. In this presentation, the most recent progress in SLS development will be presented. The presentation will also discuss the comparison of SLS with mercury–cadmium–telluride (HgCdTe) using Rule 07, SLS minority carrier lifetime issues, and future directions. [Copyright &y& Elsevier]

This paper reviews the present status and gives outlook on future developments of quantum dot infrared photodetectors (QDIPs). At the beginning the paper summarizes the fundamental properties of QDIPs. Next, an emphasize is put on their potential developments. Investigations of the performance of QDIPs as compared to other types of infrared photodetectors are presented. A model is based on fundamental performance limitations enabling a direct comparison between different infrared material technologies. It is assumed that the performance is due to thermal generation in the active detector’s region. In comparative studies, the HgCdTe photodiodes, quantum well infrared photodetectors (QWIPs), type II superllatice photodiodes, Schottky barrier photoemissive detectors, doped silicon detectors, and high temperature superconductor detectors are considered. Theoretical predictions indicate that only type II superlattice photodiodes and QDIPs are expected to compete with HgCdTe photodiodes. QDIPs theoretically have several advantages compared with QWIPs including the normal incidence response, lower dark current, higher operating temperature, higher responsivity and detectivity. The operating temperature for HgCdTe detectors is higher than for other types of photon detectors. Comparison of QDIP performance with HgCdTe detectors gives evidence that the QDIP is suitable for high operation temperature. It can be expected that improvement in technology and design of QDIP detectors will make it possible to achieve both high sensitivity and fast response useful for practical application at room temperature. Finally, issue associated with the development and exploitation of multispectral photodetectors from this new material is discussed. Discussions is focused on most recently on-going detector technology efforts in fabrication both photodetectors and focal plane arrays. [ABSTRACT FROM AUTHOR]

Recent commercial and military infrared sensors have demanded multispectral capabilities, high sensitivity and high selectivity, usually found in quantum well infrared photodetectors (QWIPs). This paper presents the design and characterization of a three-band QWIP capable to detect simultaneously near infrared (NIR), mid-wavelength infrared (MWIR), and long-wavelength infrared (LWIR), using interband and intersubband transitions. Separate readouts provide the flexibility to optimize each band detection by allowing the application of different bias voltages. The quantum well structure was designed using a computational tool developed to solve self-consistently the Schrodinger-Poisson equation with the help of the shooting method. The detector comprises of three different stacks of uncoupled (wide barriers) quantum wells that combine AlGaAs, GaAs, and InGaAs, separated by contact layers, grown by molecular beam epitaxy (MBE) on a GaAs substrate. The spectral responses in all three bands were measured using a standard photocurrent spectroscopy setup with light coupling via a 45 facet. The measured photoresponse showed peaks at 0.84, 5.0, and 8.5 wavelengths with approximately 0.8, 0.03, and 0.12 A/W peak responsivities for NIR, MWIR, and LWIR bands, respectively. A good agreement between the measured and simulated figures of merit shows the possibility to improve and tailor the detector for several applications with low computational effort. Finally, this work has demonstrated the possibility of detection of widely separated wavelength bands using interband and intersubband transitions in quantum wells. [ABSTRACT FROM PUBLISHER]

Abstract: This paper reviews the present status and possible future developments of quantum-dot infrared photodetectors (QDIPs). At the beginning the paper summarizes the fundamental properties of QDIPs. Next, an emphasis is put on their potential developments. Investigations of the performance of QDIPs as compared to other types of infrared photodetectors are presented. A model is based on fundamental performance limitations enabling a direct comparison between different infrared material technologies. It is assumed that the performance is due to thermal generation in the active detector''s region. In comparative studies, the HgCdTe photodiodes, quantum well infrared photodetectors (QWIPs), type-II superlattice photodiodes, Schottky barrier photoemissive detectors, doped silicon detectors, and high-temperature superconductor detectors are considered. Theoretical predictions indicate that only type-II superlattice photodiodes and QDIPs are expected to compete with HgCdTe photodiodes. QDIPs theoretically have several advantages compared with QWIPs including the normal incidence response, lower dark current, higher operating temperature, higher responsivity and detectivity. The operating temperature for HgCdTe detectors is higher than for other types of photon detectors. It is also shown, that BLIP temperature of QDIP strongly depends on nonuniformity in the QD size. Comparison of QDIP performance with HgCdTe detectors gives clear evidence that the QDIP is suitable for high operation temperature. It can be expected that improvement in technology and design of QDIP detectors will make it possible to achieve both high sensitivity and fast response useful for practical application at room temperature FPAs. Comparison of theoretically predicted and experimental data indicates that, as so far, the QDIP devices have not fully demonstrated their potential advantages and are expected to posses the fundamental ability to achieve higher detector performance. Poor QDIP performance is generally linked to nonoptimal band structure and controlling the QDs size and density (nonuniformity in QD size). [Copyright &y& Elsevier]

Abstract: High dynamics measurements of spectral response were carried out on quantum well infrared photodetectors (QWIP). Photocurrent spectra were studied over more than three orders of magnitude, revealing the presence of spectral structures which were never observed hitherto. Electric field assisted tunneling and, more surprisingly, Van Hove singularities at the miniband edges, are shown to play an important role in the low and high energy parts of the QWIP photocurrent spectra, respectively. These experimental features motivated us to initiate a theoretical study of the absorption in a multiquantum well structure. Our work is based on the study of the electronic wave function in a periodic structure. [Copyright &y& Elsevier]

We present a simulation based investigation of the dependence of the device characteristics on the quantum well width in AlGaAs/GaAs quantum well infrared photodetectors (QWIPs) through the ensemble Monte Carlo technique. The simulations on two different standard Al0.3Ga0.7As/GaAs QWIPs with quantum well widths of 36 and 44 Å have shown that the gain in the former is considerably higher, which is due to much longer lifetime of the photoexcited electrons as a result of lower capture probability in the device. We discuss this observation by the investigation of the electron scattering rates in these structures through realistically evaluated scattering mechanisms between two and three-dimensional states in the multi-quantum well structure. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents two test benches which were specifically developed at ONERA (French national aerospace research center) for advanced characterizations of infrared photodetectors. The first test bench relies on a Fourier Transform infrared spectrometer and delivers hyperspectral cartographies on a large spectral range (from 1.3 to 20μm), with a rather good resolution (better than 16cm−1). Hyperspectral cartographies of a 640×512 QWIP FPA prototype operating in the 8- to 10-μm spectral range are presented. Our measurements, coupled with an empirical model, allow one to extract technological parameters such as the pixels thickness or the mismatch between grating period and pixel pitch. The second test bench is dedicated to angular response measurements. The photodetector is illuminated with a blackbody with a varying angle of incidence θ. The originality of this experimental setup lies in the fact that both the detector and the blackbody are located in the same, large cryogenic assembly. Thus, the angle of incidence on the detector can be adjusted over a wide range (−80° to +80°), and measurements are performed with low background and low stray light. We present angular responses obtained on “low-noise QWIP” single elements with different etch depth of the grating and interpret them thanks to an intuitive model of grating coupling. [Copyright &y& Elsevier]

Abstract: We report the fabrication and characteristics of large format (640×512) InP/In0.53Ga0.47As long wavelength infrared (LWIR) quantum well infrared photodetector (QWIP) focal plane array (FPA). The FPA, which is hybridized to a read-out integrated circuit having a charge capacity of 1.1×107 electrons, yielded a mean noise equivalent temperature difference (NETD) of ∼40mK at a cold finger temperature as high as 77K. The performance of the FPA, being comparable to that of AlGaAs/GaAs QWIP FPAs, clearly demonstrates the feasibility of the InP/InGaAs material system as an Al-free alternative to AlGaAs/GaAs system for large format LWIR QWIP FPAs. [Copyright &y& Elsevier]

Abstract: The current noise power spectrum of a multi quantum well infrared photodetector is calculated using a Langevin-transport equation where a discrete distribution of the electric field in the quantum well region, rather than the homogeneous one valid for bulk semiconductors, has been considered. The discreteness of the electric field arises as a consequence of the discrete structure of the quantum well layers. The inhomogeneous charge distribution in the quantum well structure affects the intensity and the frequency dependence of the noise power spectrum, giving rise to deviations from the behavior expected on the basis of a simple model based on fully uncorrelated fluctuation processes. The model reproduces the different N-dependence of the current noise power spectral density in the dark and in the presence of radiation. In particular, its relation to the discrete structure of the device arises as a consequence of the imbalance between the current injected at the emitter and the stream of photoelectrons drifting through the structure, whose effect seems particularly relevant for small values of the number of quantum wells N. [Copyright &y& Elsevier]

We propose a stacked dual-band quantum well infrared photodetector (QWIP) integrated with a double-layer gold disk. Two 10-period quantum wells (QW) operating at different wavelengths are stacked together, and gold nano-disks are integrated on their respective surfaces. Numerical calculations by finite difference time domain (FDTD) showed that the best enhancement can be achieved at 13.2 and 11.0 µm. By integrating two metal disks, two plasmon microcavity structures can be formed with the substrate to excite localized surface plasmons (LSP) so that the vertically incident infrared light can be converted into electric field components perpendicular to the growth direction of the quantum well (EZ). The EZ electric field component can be enhanced up to 20 times compared to the incident light, and it is four times that of the traditional two-dimensional hole array (2DHA) grating. We calculated the enhancement factor and coupling efficiency of the device in the active region of the quantum well. The enhancement factor of the active region of the quantum well on the top layer remains above 25 at the wavelength of 13.2 μm, and the enhancement factor can reach a maximum of 45. Under this condition, the coupling efficiency of the device reaches 2800%. At the wavelength of 11.0 μm, the enhancement factor of the active region of the quantum well at the bottom is maintained above 6, and the maximum can reach about 16, and the coupling efficiency of the device reaches 800%. We also optimized the structural parameters and explored the influence of structural changes on the coupling efficiency. When the radius (r1, r2) of the two metal disks increases, the maximum coupling efficiency will be red-shifted as the wavelength increases. The double-layer gold disk structure we designed greatly enhances the infrared coupling of the two quantum well layers working at different wavelengths in the dual-band quantum well infrared photodetector. The structure we designed can be used in stacked dual-band quantum well infrared photodetectors, and the active regions of quantum wells working at two wavelengths can enhance the photoelectric coupling, and the enhancement effect is significant. Compared with the traditional optical coupling structure, the structure we proposed is simpler in process and has a more significant enhancement effect, which can meet the requirements of working in complex environments such as firefighting, night vision, and medical treatment. [ABSTRACT FROM AUTHOR]

Enhancing active material absorption and suppressing ohmic loss is desired by a lot of applications based on plasmonic structures. In this work, an effective photonic approach is presented to achieve this purpose in plasmonic cavities. Enhancing the absorption ratio of the active material to the metal (by properly increasing the volume of the active region), and meanwhile keeping the system close to a critical coupling status for perfect light trapping (by switching the resonance to a higher‐order one or making real facets as the cavity boundaries) is proposed. As a photonic approach, this is generally applicable to different plasmonic materials. With the help of this approach, the absorption of the quantum wells in a plasmonic‐cavity‐integrated quantum well infrared photodetector operating in the longwave infrared range can be enhanced to 82% of the incident power and the ohmic loss can be suppressed to 18%. For plasmonic‐cavity‐integrated GaAs devices operating in the near infrared range, the approach can enhance the active material absorption to 78% of the incident power and suppress the ohmic loss to 20% at the wavelengths close to the bandgap. Also, it would improve the performance at a more extended wavelength. [ABSTRACT FROM AUTHOR]

Herein, two challenges are addressed, which quantum well infrared photodetectors (QWIPs), based on III‐V semiconductors, face, namely: photodetection within the so‐called "forbidden gap", between 1.7 and 2.5 microns, and room temperature operation using thermal sources. First, to reach this forbidden wavelength range, a QWIP which consists of a superlattice structure with a central quantum well (QW) with a different thickness is presented. The different QW in the symmetric structure, which plays the role of a defect in the otherwise periodic structure, gives rise to localized states in the continuum. The proposed InGaAs/InAlAs superlattice QWIP detects radiation around 2.1 microns, beyond the materials bandoffset. Additionally, the wavefunction parity anomaly is explored to increase the oscillator strength of the optical transitions involving higher order states. Second, with the purpose of achieving room temperature operation, an asymmetric InGaAs/InAlAs superlattice, in which the QW with a different thickness is not in the center, is used to detect infrared radiation around 4 microns at 300 K. This structure operates in the photovoltaic mode because it gives rise to states in the continuum which are localized in one direction and extended in the other, leading to a preferential direction for current flow. [ABSTRACT FROM AUTHOR]