Low Crosstalk Three-Color Infrared Detector by Controlling the Minority Carriers Type of InAs/GaSb Superlattices for Middle-Long and Very-Long Wavelength

We report a type-Ⅱ InAs/GaSb superlattice three-color infrared detector for mid-wave （MW）, long-wave （LW）, and very long-wave （VLW） detections. The detector structure consists of three contacts of NIPIN architecture for MW and LW detections, and hetero-junction NIP architecture for VLW detection. It is found that the spectral crosstalks can be significantly reduced by controlling the minority carriers transport via doping beryllium in the two active regions of NIPIN section. The crosstalk detection at MW, LW, and VLW signals are achieved by selecting the bias voltages on the device. At 77K, the cutoff wavelengths of the three-color detection are 5.3μm （at OmV）, 141μm （at 300mV） and 19μm （at -20mV） with the detectivities of 4.6xlO11 cm.Hzl/ZW-1, 2.3×10^10 cm.Hzl/2W-1, and 1.0×10^10cm.Hzl/2W-1 for MW, LW and VLW. The crosstalks of the MW channel, LW channel, and VLW channel are almost 0, 0.25, and 0.6, respectively.

Improvement of tunnel compensated quantum well infrared detector

To reduce the difficulty of the epitaxy caused by multiple quantum well infrared photodetector(QWIP)with tunnel compensation structure,an improved structure is proposed.In the new structure,the superlattices are located between the tunnel junction and the barrier as the infrared absorption region,eliminating the effect of doping concentration on the well width in the original structure.Theoretical analysis and experimental verification of the new structure are carried out.The experimental sample is a two-cycle device,each cycle contains a tunnel junction,a superlattice infrared absorption region and a thick barrier.The photosurface of the detector is 200×200μm^2 and the light is optically coupled by 45°oblique incidence.The results show that the optimal operating voltage of the sample is-1.1 V,the dark current is 2.99×10^-8A,and the blackbody detectivity is1.352×10^8 cm·Hz^1/2·W^-1at 77 K.Our experiments show that the new structure can work normally.

High-performance midwavelength infrared detectors based on InAsSb nBn design

we report n Bn photodetectors based on In As0.91 Sb0.09 with a 100% cut-off wavelength of 4.75 μm at 300 K. The band of an n Bn detector is similar to that of a standard pin detector, but there is special wide bandgap Al As0.08 Sb0.92 barrier layer in the n Bn detector, in which the depletion region of n Bn detector exists. The n Bn design has many advantages, such as low dark current and high quantum efficiency, because the n Bn design can suppress the generation–recombination(GR)current that is the main composition of standard pin detector dark current. The constant slope of the Arrhenius plot of J0–1/T indicates the absence of the generation–recombination dark current. We fabricate an n Bn detector with a quantum efficiency(QE) maximum of ~ 60% under-0.2-V bias voltage. The In As Sb n Bn detectors may be a competitive candidate for midwavelength infrared detector.

MOCVD Ga_xIn_(1-x)As_(1-y)Sb_y Alloys and the Infrared Detector

Ga_xIn_(1-x)As_(1-y)Sb_y alloys have been grown by atmospheric pressure MOCVD on n-GaSb(Te-doped) substrate.The sohd composition was determined by using electron microprobe.The alloys of GalnAsSb with composition in miscibility gap were successfully grown.The optical properties of Ga_xIn_(1-x)As_(1-y)Sb_y lavers were characterized by the photoluminescence and the infrared absorption.The spectral responses of p^+-GaInAsSb/p-Ga_xIn_(1-x)As_(1-y)Sb_y/n-GaSb detectors showed wavelength cut off at 2.4μm and detectivity- D~*=5×10~8 cmHz^(1/2)/W at room temperature.

Wet etching and passivation of GaSb-based very long wavelength infrared detectors

The etching and passivation processes of very long wavelength infrared(VLWIR)detector based on the InAs/GaSb/AlSb type-II superlattice have been studied.By studying the effect of each component in the citric acid solution(citric acid,phosphoric acid,hydrogen peroxide,deionized water),the best solution ratio is obtained.After comparing different passivation materials such as sulfide+SiO_(2),Al_(2)O_(3),Si_(3)N_(4) and SU8,it is found that SU8 passivation can reduce the dark current of the device to a greater degree.Combining this wet etching and SU8 passivation,the of VLWIR detector with a mesa diameter of 500μm is about 3.6Ω·cm^(2) at 77 K.

Molecular-beam epitaxy-grown HgCdTe infrared detector:Material physics, structure design, and device fabrication

Infrared(IR) detectors have important applications in numerous civil and military sectors. Hg Cd Te is one of the most important materials for IR detector manufacture. This review systematically discusses the progress of Hg Cd Te materials grown via molecular-beam epitaxy(MBE) for IR detection in terms of material physics, structure design, and fabrication. The material physics of Hg Cd Te includes crystal information, band structure, and electrical and optical properties. The characterization methods of the As-grown Hg Cd Te materials are also summarized. Then, four design structures of Hg Cd Te for IR detectors, with multilayer, superlattice, double-layer heterojunction, and barrier properties, which significantly improve the device performance,are discussed. The third section summarizes the studies on Hg Cd Te MBE-grown on different substrates, including Cd Zn Te, Si,and Ga Sb, in recent decades. This review discusses the factors influencing the growth of the Hg Cd Te film and their relationships and optimal conditions. Finally, we present the prospects and challenges associated with the fabrication and applications of Hg Cd Te materials for IR detectors.

On-orbit geometric calibration of satellite laser altimeters using infrared detectors and corner-cube retroreflectors

After being launched into orbit,the geometric calibration of a satellite laser altimeter will reduce errors in laser pointing and ranging caused by satellite vibrations during launch,environmental changes,and thermal effects during long-term operation,which guarantees the accuracy of measurement data.In this study,a satellite laser geometric calibration method combining infrared detectors and corner-cube retroreflectors(CCRs)is proposed.First,a CCR-based laser ranging error calibration method was established,and then a laser pointing error calibration model was derived based on a single infrared detector array.Taking GaoFen-7(GF-7)satellite laser beam 2 as the experimental object,laser geometric calibration was realized using an infrared detector and CCR-measured data.Then,the accuracy of the proposed method was compared with that of other calibration methods,the CMLID and the CMSPR.The results show that the accuracy of the proposed calibration method is equivalent to that of the CMLID and higher than that of the CMSPR.Among them,the accuracy of the laser pointing after calibration using the proposed method is better than 0.8 arcsec,and the elevation accuracy of the laser on flat,sloping,and mountainous terrains is better than 0.11 m,0.30 m,and 1.80 m,respectively.

Progress and challenges in blocked impurity band infrared detectors for space-based astronomy

Astronomical detection at infrared wavelengths is crucial in astrophysics due to the critical information in this wavelength range.Blocked impurity band(BIB) infrared detectors are desirable for space-based astronomical observation due to their broad response range, low dark currents, high quantum efficiencies, and excellent radiation resistance. In this review, typical BIB device structures and device physics development are first introduced. Subsequently, we discuss progress in Si-based BIB detectors with different doping types and emphasize their applications in space-based infrared detection. Additionally, we discuss recent efforts on pixel performance optimization, response extension, and higher operating temperature devices. Finally,we conclude by proposing the challenges and perspectives of BIB detectors with improved detection performances.

The theory and experiment of very-long-wavelength 256×1 GaAs/Al_(x)Ga_(1-x)As quantum well infrared detector linear arrays

The 256×1 linear array of multiple quantum wells infrared photodetector (QWIP) is designed and fabricated for the peak response wavelength at λP=14.6 μm. The response spectral width is bigger than 2.2 μm. The two-dimensional (2D) diffractive coupling grating has been formed on the top QWIP photosensitive pixel for coupling the infrared radiation to the infrared detective layers. The performance of the device at VB=3 V and T=45 K has the responsibility 4.28×10-2 (A/W), the blackbody detectivity Db*=5.14×109 (cm·Hz1/2/W), and the peak detectivity Dλ*=4.24× 1010 (cm·Hz1/2/W). The sensor pixels are connected with CMOS read out circuit (ROC) hybridization by indium bumps. When integral time is 100 μs, the linear array has the effective pixel of QWIP FPA Nef of 99.2%, the average responsibility  (V/W) of 3.48×106 (V/W), the average peak detectivity Dλ* of 8.29×109 (cm·Hz1/2/W), and the non-uniformity UR of 5.83%. This device is ready for the thermal image application.

Development of Low Dark Current SiGe Near-Infrared PIN Photodetectors on 300 mm Silicon Wafers

SiGe offers a low-cost alternative to conventional infrared sensor material systems such as InGaAs, InSb, and HgCdTe for developing near-infrared (NIR) photodetector devices that do not require cooling and can operate with relatively low dark current. As a result of the significant difference in thermal expansion coefficients between germanium (Ge) and silicon (Si), tensile strain incorporated into SiGe detector devices through specialized growth processes can extend their NIR wavelength range of operation. We have utilized high throughput, large-area complementary metal-oxide semiconductor (CMOS) technology to fabricate Ge based p-i-n (PIN) detector devices on 300 mm Si wafers. The two-step device fabrication process, designed to effectively reduce the density of defects and dislocations arising during deposition that form recombination centers which can result in higher dark current, involves low temperature epitaxial deposition of Ge to form a thin p+ seed layer, followed by higher temperature deposition of a thicker Ge intrinsic layer. Phosphorus was then ion-implanted to create devices with n+ regions of various doping concentrations. Secondary ion mass spectroscopy (SIMS) has been utilized to determine the doping profiles and material compositions of the layers. In addition, electrical characterization of the I-V photoresponse of different devices from the same wafer with various n+ region doping concentrations has demonstrated low dark current levels (down to below 1 nA at -1 V bias) and comparatively high photocurrent at reverse biases, with optimal response for doping concentration of 5 × 1019 cm-3.

Graphene-aluminum nitride NEMS resonant infrared detector

The use of micro-/nanoelectromechanical resonators for the room temperature detection of electromagnetic radiation at infrared frequencies has recently been investigated,showing thermal detection capabilities that could potentially outperform conventional microbolometers.The scaling of the device thickness in the nanometer range and the achievement of high infrared absorption in such a subwavelength thickness,without sacrificing the electromechanical performance,are the two key challenges for the implementation of fast,high-resolution micro-/nanoelectromechanical resonant infrared detectors.In this paper,we show that by using a virtually massless,high-electrical-conductivity,and transparent graphene electrode,floating at the van der Waals separation of a few angstroms from a piezoelectric aluminum nitride nanoplate,it is possible to implement ultrathin(460 nm)piezoelectric nanomechanical resonant structures with improved electromechanical performance(450% improved frequency×quality factor)and infrared detection capabilities(4100×improved infrared absorptance)compared with metal-electrode counterparts,despite their reduced volumes.The intrinsic infrared absorption capabilities of a submicron thin graphene–aluminum nitride plate backed with a metal electrode are investigated for the first time and exploited for the first experimental demonstration of a piezoelectric nanoelectromechanical resonant thermal detector with enhanced infrared absorptance in a reduced volume.Moreover,the combination of electromagnetic and piezoelectric resonances provided by the same graphene–aluminum nitride-metal stack allows the proposed device to selectively detect short-wavelength infrared radiation(by tailoring the thickness of aluminum nitride)with unprecedented electromechanical performance and thermal capabilities.These attributes potentially lead to the development of uncooled infrared detectors suitable for the implementation of high performance,miniaturized and power-efficient multispectral infrared imaging systems.

CVD preparation of vertical graphene nanowalls/VO_(2)(B)composite films with superior thermal sensitivity in uncooled infrared detector

Vanadium dioxide with superior thermal sensitivity is one of the most preferred materials used in microbolometer,and the B phase of VO_(2) is particularly prominent.However,conventional VO_(2)(B)undergoes low temperature-coefficient of resistance(TCR)values and large resistances.In this paper,simple controllable composite films of vertical graphene nanowalls/VO_(2)(B)(i.e.,VGNWs/VO_(2)(B))with a suitable square resistance(12.98 kU)and a better temperature-coefficient of resistance(TCR)(-3.2%/K)were prepared via low pressure chemical vapor deposition.The VGNWs can provide a fast channel for electron transport and enhance the conductivity of VO_(2)(B).This preparation method can provide a low cost,facile and simple pathway for the design and fabrication of high performance VO_(2)(B)thin films with superior electrical properties for its application in uncooled infrared detectors.

A low-cost infrared absorbing structure for an uncooled infrared detector in a standard CMOS process

This paper introduces a low-cost infrared absorbing structure for an uncooled infrared detector in a standard 0.5 m CMOS technology and post-CMOS process. The infrared absorbing structure can be created by etching the surface sacrificial layer after the CMOS fabrication, without any additional lithography and deposition procedures. An uncooled infrared microbolometer is fabricated with the proposed infrared absorbing structure.The microbolometer has a size of 6565 m2and a fill factor of 37.8%. The thermal conductance of the microbolometer is calculated as 1.3310 5W/K from the measured response to different heating currents. The fabricated microbolometer is irradiated by an infrared laser, which is modulated by a mechanical chopper in a frequency range of 10–800 Hz. Measurements show that the thermal time constant is 0.995 ms and the thermal mass is 1.3210 8J/K. The responsivity of the microbolometer is about 3.03104V/W at 10 Hz and the calculated detectivity is 1.4108cm Hz1=2/W.

Surface plasmon-enhanced dual-band infrared absorber for VO_x-based microbolometer application

We propose a periodic structure as an extra absorption layer（i.e., absorber） based on surface plasmon resonance effects, enhancing dual-band absorption in both middle wavelength infrared（MWIR） and long wavelength infrared（LWIR）regions. Periodic gold disks are selectively patterned onto the top layer of suspended SiN/VO_2/SiN sandwich-structure.We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak. Simulation results show that the absorber has two absorption peaks at wavelengths λ =4.8 μm and λ = 9 μm with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions, respectively. In addition, the absorber achieves broad spectrum absorption in LWIR region, in the meanwhile, tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk. Thus, this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector, furthermore, the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.

Advantages of QWIP technology in infrared thermal cameras

Standard GaAs/AlGaAs quantum well infrared photodetectors(QWIP)have been seriously considered as atechnological choice for the 3^(rd) generation of thermal imagers in the long wave infrared band(LWIR)for some time.Alternative technology like MCT(HgCdTe)was the technology choice of the 2^(nd) generation because of its high quantum efficiency.In the paper,measurements on the QWIP technology will be presented and a comparison with alternative technology will be done.

Design and modeling of high‑performance mid‑wave infrared InAsSb‑based nBn photodetector using barrier band engineering approaches

We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB)layers are suggested,the advantage of which is creation of a near zero valence band ofset in nBn photodetectors.The design of theδ-DCGB nBn-PD device includes a 3µm absorber layer(n-InAs0.81Sb0.19),a unipolar barrier layer(AlSb),and 0.2μm contact layer(n-InAs0.81Sb0.19)as well as a 0.116µm linear grading region(InAlSb)from the contact to the barrier layer and also from the barrier to the absorber layer.The analysis includes various dark current contributions,such as the Shockley-Read-Hall(SRH),trap-assisted tunneling(TAT),Auger,and Radiative recombination mechanisms,to acquire more precise results.Consequently,we show that the method used in the nBn device design leads to difusion-limited dark current so that the dark current density is 2.596×10^(−8)A/cm^(2)at 150 K and a bias voltage of−0.2 V.The proposed nBn detector exhibits a 50%cutof wavelength of more than 5µm,the peak current responsivity is 1.6 A/W at a wavelength of 4.5µm and a−0.2 V bias with 0.05 W/cm2 backside illumination without anti-refective coating.The maximum quantum efciency at 4.5µm is about 48.6%,and peak specifc detectivity(D*)is of 3.37×10^(10)cm⋅Hz1/2/W.Next,to solve the refection concern in this nBn devices,we use a BaF_(2)anti-refection coating layer due to its high transmittance in the MWIR window.It leads to an increase of almost 100%in the optical response metrics,such as the current responsivity,quantum efciency,and detectivity,compared to the optical response without an anti-refection coating layer.

Thermal and mechanical characterizations of a substrate-free focal plane array

We propose a substrate-free focal plane array （FPA） and the microcantilevers extend from a supporting frame. in this paper. The solid substrate is completely removed, Using finite element analysis, the thermal and mechanical characterizations of the substrate-free FPA are presented. Because of the large decrease in thermal conductance, the supporting frame is temperature dependent, which brings out a unique feature： the lower the thermal conductance of the supporting frame is, the higher the energy conversion efficiency in the substrate-free FPA will be. The results from the finite element analyses are consistent with our measurements： two types of substrate-free FPAs with pixel sizes of 200×200 and 60×60 um^2 are implemented in the proposed infrared detector. The noise equivalent temperature difference （NETD） values are experimentally measured to be 520 and 300 mK respectively. Further refinements are considered in various aspects, and the substrate-free FPA with a pixel size of 30×30 um^2 has a potential of achieving an NETD value of 10 mK.

Preparation of LPE GaInAsSb Epilayers and Its Photodiodes for Detection of 1．8～2．1μm

Growth of GaInAsSb epilayer by liquid phase epitaxy (LPE) was reported. The LPE system with a hor-izontal sliding graphite boat was employed. The Te-doped (100) GaSb wafer was chosen as substrate. Thephysical properties of the GalnAsSb / GaSb heterostructure were investigated by double crystal X-ray rock-ing diffraction and photoluminescence. The p-GaInAsSb/ n-GaSb photodiode was made by using theseheterostructure materials .The detectivity of the photodiode D* is 4.65 ×10￣9 cm . Hz￣(1 /2) W￣(-1).

Dielectric Characteristics of Ba_(0.65)Sr_(0.35)TiO_3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3 （BST） thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 μ℃/cm^2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 ℃ exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 ℃. The dielectric loss tangent of BST thin fdms at 100 kHz is less than 0.04. As a result, the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.

Spectral selectivity in infrared thermal detection

A review is made of the physics and technology of spectrally selective thermal detectors,especially those operating at non-cryogenic temperatures.The background radiation noise fluctuations are rederived for arbitrary spectral characteristics.Infrared absorption due to phonons and free carriers is discussed followed by a review of published works on artificial infrared absorption materials such as patterned grids,nanoparticles,plasmonic structures,metamaterials and others.Subsequently,the literature of the spectral characteristics of broadband thermal detectors and spectrally selective thermal detectors is reviewed.Finally,the authors speculate on the directions that future research and development in the area will take regarding architectures,sensitivity and spectral characteristics.