The measurement of responsivity of infrared photodetectors using a cavity blackbody

For the measurement of responsivity of an infrared photodetector,the most-used radiation source is a blackbody.In such a measurement system,distance between the blackbody,the photodetector and the aperture diameter are two parameters that contribute most measurement errors.In this work,we describe the configuration of our responsivity measurement system in great detail and present a method to calibrate the distance and aperture diameter.The core of this calibration method is to transfer direct measurements of these two parameters into an extraction procedure by fitting the experiment data to the calculated results.The calibration method is proved experimentally with a commercially extended InGaAs detector at a wide range of blackbody temperature,aperture diameter and distance.Then proof procedures are further extended into a detector fabricated in our laboratory and consistent results were obtained.

9μm Cutoff 128×128 AlGaAs/GaAs Quantum Well Infrared Photodetector Focal Plane Arrays

We design and fabricate a 128 × 128 AlGaAs/GaAs quantum well infrared photodetector focal plane array （FPA）. The device is achieved by metal organic chemical vapor deposition and GaAs integrated circuit processing technology. A test structure of the photodetector with a mesa size of 300μm × 300μm is also made in order to obtain the device parameters. The measured dark current density at 77K is 1.5 × 10^-3A/cm^2 with a bias voltage of 2V. The peak of the responsivity spectrum is at 8.4μm,with a cutoff wavelength of 9μm. The blackbody detectivity is shown to be 3.95 × 10^8 （cm · Hz^1/2）/W. The final FPA is flip-chip bonded on a CMOS read-out integrated circuit. The infrared thermal images of some targets at room temperature background are successfully demonstrated at 80K operating temperature with a ratio of dead pixels of less than 1%.

Injector Quantum Dot Molecule Infrared Photodetector:A Concept for Efficient Carrier Injection

Quantum dot infrared photodetectors are expected to be a competitive technology at high oper ation temperatures in the long and very long wavelength infrared spectral range.Despite the fact that they already achieved notable success,the performance suffers from the thermionic emission of electrons from the quantum dots at elevated temperatures resulting in a decreasing responsivity.In order to provide an efficient carrier injection at high temperatures,quantum dot infrared photodetectors can be separated into two parts:an injection part and a detection part,so that each part can be separately optimized.In order to integrate such functionality into a device,a new class of quantum dot infrared photodetectors using quantum dot molecules will be introduced.In addition to a general discussion simulation results suggest a possibility to realize such a device.

Facile sensitizing of PbSe film for near-infrared photodetector by microwave plasma processing

High quality PbSe film was first fabricated by a thermal evaporation method, and then the effect of plasma sensitization on the PbSe film was systemically investigated. Typical detectivity and significant photosensitivity are achieved in the PbSe-based photodetector, reaching maximum values of 7.6 × 10^(9)cm·Hz^(1/2)/W and 1.723 A/W, respectively. Compared with thermal annealing, plasma sensitization makes the sensitization easier and significantly improves the performance.

New materials and designs for 2D-based infrared photodetectors

Infrared photodetectors have attracted much attention considering their wide civil and military applications.Two-dimensional(2D)materials offer new opportunities for the development of costless,high-level integration and high-performance infrared photodetectors.With the advent of a broad investigation of infrared photodetectors based on graphene and transition metal chalcogenides(TMDs)exhibiting unique properties in recent decades,research on the better performance of 2D-based infrared photodetectors has been extended to a larger scale,including explorations of new materials and artificial structure designs.In this review,after a brief background introduction,some major working mechanisms,including the photovoltaic effect,photoconductive effect,photogating effect,photothermoelectric effect and bolometric effect,are briefly offered.Then,the discussion mainly focuses on the recent progress of three categories of 2D materials beyond graphene and TMDs.Noble transition metal dichalcogenides,black phosphorus and arsenic black phosphorous and 2D ternary compounds are great examples of explorations of mid-wavelength or even long-wavelength 2D infrared photodetectors.Then,four types of rational structure designs,including type-II band alignments,photogating-enhanced designs,surface plasmon designs and ferroelectric-enhanced designs,are discussed to further enhance the performance via diverse mechanisms,which involve the narrower-bandgap-induced interlayer exciton transition,gate modulation by trapped carriers,surface plasmon polaritons and ferroelectric polarization in sequence.Furthermore,applications including imaging,flexible devices and on-chip integration for 2D-based infrared photodetectors are introduced.Finally,a summary of the state-of-the-art research status and personal discussion on the challenges are delivered.

Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors

For non-destructive optical characterization, laser beam induced current(LBIC) microscopy has been developed into as a quantitative tool to examine individual photodiodes within a large pixel array. Two-dimensional LBIC microscopy, also generally called photocurrent mapping(PC mapping), can provide spatially resolved information about local electrical properties and p-n junction formation in photovoltaic infrared(including visible light) photodetectors from which it is possible to extract material and device parameters such as junction area, junction depth, diffusion length, leakage current position and minority carrier diffusion length etc. This paper presents a comprehensive review of research background, operating principle, fundamental issues, and applications of LBIC or PC mapping.

High-sensitivity shortwave infrared photodetectors of metal-organic frameworks integrated on 2D layered materials

Photodetectors operating in the shortwave infrared region are of great significance due to their extensive applications in both commercial and military fields.Narrowbandgap two-dimensional layered materials(2DLMs)are considered as the promising candidates for constructing nextgeneration high-performance infrared photodetectors.Nevertheless,the performance of 2DLMs-based photodetectors can hardly satisfy the requirements of practical applications due to their weak optical absorption.In the present study,a strategy was proposed to design high-performance shortwave infrared photodetectors by integrating metalorganic frameworks(MOFs)nanoparticles with excellent optical absorption characteristics and 2DLM with high mobility.Further,this study demonstrated the practicability of this strategy in a MOF/2DLM(Ni-CAT-1/Bi_(2)Se_(3))hybrid heterojunction photodetector.Due to the transfer of photo-generated carriers from the MOF to Bi_(2)Se_(3),the MOF nanoparticles integrated on the Bi_(2)Se_(3) layer can increase the photocurrent by 2-3 orders of magnitude.The resulting photodetector presented a high responsivity of 4725 A W^(−1) and a superior detectivity of 3.5×10^(13) Jones at 1500 nm.The outstanding performance of the hybrid heterojunction arises from the synergistic function of the enhanced optical absorption and photogating effect.In addition,the proposed device construction strategy combining MOF photosensitive materials with 2DLMs shows a high potential for the future high-performance shortwave infrared photodetectors.

Recent developments of infrared photodetectors with lowdimensional inorganic nanostructures

Low-dimensional inorganic nanostructures such as quantum dots as well as one-and two-dimensional nanostructures are widely studied and already used in high-performance infrared photodetectors.These structures feature large surface-to-volume ratios,tunable light absorption,and electron-limiting effects.This article reviews the state-of-the-art research of low-dimensional inorganic nanostructures and their application for infrared photodetection.Thanks to nano-structuring,a narrow bandgap,hybrid systems,surface-plasmon resonance,and doping,many common semiconductors have the potential to be used for infrared detection.The basic approaches towards infrared detection are summarized.Furthermore,a selection of very important and special nanostructured materials and their remarkable infrared-detection properties are introduced(e.g.,black phosphorus,graphene-based,MoX_(2)-based,Ⅲ-Ⅶ group).Each section in this review describes the corresponding photosensitive properties in detail.The article concludes with an outlook of anticipated future developments in the field.

Vapor phase growth of two-dimensional PdSe2 nanosheets for high-photoresponsivity near-infrared photodetectors

Palladium diselenide(PdSe2),a stable layered material with pentagonal structure,has attracted extensive interest due to its excellent electrical and optoelectronic performance.Here,we report a reliable process to synthesize PdSe2 via chemical vapor deposition(CVD)method.Through systematic regulation of temperature in the growth process,we can tune the thickness,size,nucleation density and morphology of PdSe2 nanosheets.Field-effect transistors based on PdSe2 nanosheets exhibit n-type behavior and present a high electron mobility of 105 cm^2·V^−1·s^−1.The electrical property of the devices after 6 months keeping in the air show little change,implying outstanding air-stability of PdSe2.In addition,PdSe2 near-infrared photodetector shows a photoresponsivity of 660 A·W^−1 under 914 nm laser.These performances are better than those of most CVD-grown 2D materials,making ultrathin PdSe2 a highly qualified candidate material for next-generation optoelectronic applications.

Flexible Transparent Near-Infrared Photodetector Based on 2D Ti_(3)C_(2) MXene-Te Van Der Waals Heterostructures

Ti_(3)C_(2) MXe ne servi ng as superior electrical con ductors prese nts more specific performa nee such as tran spar ency,con ductivity tha n gold(Au),and even could form a heterostructure with active materials of the functional devices.Here,a Ti_(3)C_(2) MXene-Te microplate van der Waals heterostructure based tran spare nt near-i nfrared photodetector(PD)is exploited.

Strain effect on intersubband transitions in rolled-up quantum well infrared photodetectors

Pre-strained nanomembranes with four embedded quantum wells（QWs） are rolled up into threedimensional（3D） tubular QW infrared photodetectors（QWIPs）,which are based on the QW intersubband transition（ISBT）.A redshift of ～0.42 meV in photocurrent response spectra is observed and attributed to two strain contributions due to the rolling of the pre-strained nanomembranes.One is the overall strain that mainly leads to a redshift of ～0.5 meV,and the other is the strain gradient which results in a very tiny variation.The blue shift of the photocurrent response spectra with the external bias are also observed as quantum-confined Stark effect（QCSE）in the ISBT.

Long wavelength interband cascade photodetector with type Ⅱ InAs/GaSb superlattice absorber

We report on a long wavelength interband cascade photodetector with type Ⅱ InAs/GaSb superlattice absorber.The device is a three-stage interband cascade structure.At 77 K,the 50%cutoff wavelength of the detector is 8.48μm and the peak photoresponse wavelength is 7.78μm.The peak responsivity is 0.93 A/W and the detectivity D*is 1.12×10^(11)cm·Hz0.5/W for 7.78μm at-0.20 V.The detector can operate up to about 260 K.At 260 K,the 50%cutoff wavelength is 11.52μm,the peak responsivity is 0.78 A/W and the D*is 5.02×10^(8)cm·Hz0.5/W for the peak wavelength of 10.39μm at-2.75 V.The dark current of the device is dominated by the diffusion current under both a small bias voltage of-0.2 V and a large one of-2.75 V for the temperature range of 120 to 260 K.

QUANTUM MECHANICAL MODEL AND SIMULATION OF GaAs/AlGaAs QUANTUM WELL INFRARED PHOTO-DETECTOR-ⅠOPTICAL ASPECTS

A complete quantum mechanical model for GaAs?AlGaAs quantum well infrared photodetectors(QWIPs) is presented here. The model consisted of four parts: (1) Starting with the description of the electromagnetic field of the infrared radiation in the QWIP, effective component of the vector potential <| A z |> along the QWIP growth direction ( z axis) due to the optical diffraction grating was calculated. (2) From the wave transmissions and the occupations of the electronic states, it was discussed that the dark current in the QWIP is determined by the drift diffusion current of carriers thermally excited from the ground sublevel in the quantum well to extended states above the barrier. (3) The photocurrent was investigated by the optical transition (absorption coefficient between the ground state to excited states due to the nonzero <| A z |> ). (4) By studying the inter diffusion of the Al atoms across the GaAs?AlGaAs heterointerfaces,the mobility of the drift diffusion carriers in the excited states was calculated, so the measurement results of the dark current and photocurrent spectra can be explained theoretically. With the complete quantum mechanical descriptions of (1 4), QWIP device design and optimization are possible.

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.

Mid-wavelength nBn photodetector with high operating temperature and low dark current based on InAs/InAsSb superlattice absorber

In this paper,we demonstrate nBn InAs/InAsSb type II superlattice(T2SL)photodetectors with AlAsSb as the barrier that targets mid-wavelength infrared(MWIR)detection.To improve operating temperature and suppress dark current,a specific Sb soaking technique was employed to improve the interface abruptness of the superlattice with device passivation using a SiO_(2) layer.These result in ultralow dark current density of 6.28×10^(-6)A/cm^(2)and 0.31 A/cm^(2)under-600 mV at 97 K and297 K,respectively,which is lower than most reported InAs/InAsSb-based MWIR photodetectors.Corresponding resistance area product values of 3.20×10^(4)Ω·cm^(2)and 1.32Ω·cm^(2)were obtained at 97 K and 297 K.A peak responsivity of 0.39 A/W with a cutoff wavelength around 5.5μm and a peak detectivity of 2.1×10^(9)cm·Hz^(1/2)/W were obtained at a high operating temperature up to 237 K.

Broadening of Photoluminescence by Nonhomogeneous Size Distribution of Self-Assembled InAs Quantum Dots

The photoluminescence spectrum （PL） of InAs quantum dots （QDs） at 80 K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the size distribution of QDs. Its mean volume and the standard full width at half maximum （FWHM） of the PL spectrum. size deviation are well correlated with the peak and The experimental PL spectrum is well reproduced by the theoretical model based on the effect mass approximation including the size distribution without any adjustable parameters. Compared with the standard size deviation value σ = 9 × 10^-2 determined by atomic force microscopic method a small value σ = 7 × 10^-2 is obtained by the best fitting process from the measured and calculated PL spectra.

III-Nitride-Based Quantum Dots and Their Optoelectronic Applications

During the last two decades, III-nitride-based quantum dots(QDs) have attracted great attentions for optoelectronic applications due to their unique electronic properties. In this paper, we first present an overview on the techniques of fabrication for III-nitride-based QDs. Then various optoelectronic devices such as QD lasers, QD light-emitting diodes(LEDs), QD infrared photodetectors(QDIPs) and QD intermediate band(QDIB) solar cells(SCs) are discussed. Finally, we focus on the future research directions and how the challenges can be overcome.

Picosecond electrical response in graphene/MoTe_(2) heterojunction with high responsivity in the near infrared region

Understanding the fundamental charge carrier dynamics is of great significance for photodetectors with both high speed and high responsivity.Devices based on two-dimensional(2D)transition metal dichalcogenides can exhibit picosecond photoresponse speed.However,2D materials naturally have low absorption,and when increasing thickness to gain higher responsivity,the response time usually slows to nanoseconds,limiting their photodetection performance.Here,by taking time-resolved photocurrent measurements,we demonstrated that graphene/MoTe_(2) van der Waals heterojunctions realize a fast 10 ps photoresponse time owing to the reduced average photocurrent drift time in the heterojunction,which is fundamentally distinct from traditional Dirac semimetal photodetectors such as graphene or Cd_(3)As_(2) and implies a photodetection bandwidth as wide as 100 GHz.Furthermore,we found that an additional charge carrier transport channel provided by graphene can ef-fectively decrease the photocurrent recombination loss to the entire device,preserving a high responsivity in the near-infrared region.Our study provides a deeper understanding of the ultrafast electrical response in van der Waals heterojunctions and offers a promising approach for the realization of photodetectors with both high responsivity and ultrafast electrical response.

Topological crystalline insulator nanomembrane with strain-tunable band gap

The ability to fine-tune band gap and band inversion in topological materials is highly desirable for the development of novel functional devices. Here we propose that the electronic properties of free-standing nanomernbranes of the topological crystalline insulators （TCI） SnTe and Pb1-xSnx（Se,Te） are highly tunable by engineering elastic strain and membrane thickness, resulting in tunable band gap and giant piezoconductivity. Membrane thickness governs the hybridization of topological electronic states on opposite surfaces, while elastic strain can further modulate the hybridization strength by controlling the penetration length of surface states. We propose a frequency-resolved infrared photodetector using force-concentration induced inhomogeneous elastic strain in TCI nanomembranes with spatially varying width. The predicted tunable band gap accompanied by strong spin-textured electronic states will open new avenues for fabricating piezoresistive devices, infrared detectors and energy-efficient electronic and spintronic devices based on TCI nanomembrane.

Characterization and performance of graphene-PbSe thin film heterojunction

An infrared detector with high responsivity based on graphene-PbSe thin film heterojunction was reported.High-quality PbSe thin film and graphene were prepared by molecular beam epitaxy and chemical vapor deposition,respectively.The physical characteristics of PbSe thin film and graphene were performed using X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and Raman measurement.The photo transistor using PbSe thin film as a sensitizer and graphene as a channel to transport excitons exhibits peak responsivity and detectivity up to~420 A·W^(-1) and 5.9×10^(11) Jones(radiation intensity:0.75 mW·cm^(-2))at room temperature in the near-infrared(NIR)region,respectively.The high optical response is attributed to the photo-excited holes transferring from PbSe film to graphene under irradiation.Moreover,it is revealed that the responsivity of graphene-PbSe photo transistor is gate-tunable which is important in photodetectors.