Photoconductive PbSe thin films for infrared imaging

Harrison J.T., Pantoja E., Jang M., Gupta M.C.

Interests in group IV-VI compound semiconductors for MWIR applications have undergone multiple resurgences over the last 70 years due to the high IR responsivity. Many research groups have shown they can achieve high IR response by making modification of the sensitization process; however, nearly all are using traditional deposition methods (Chemical Bath Deposition or Chemical/Physical Vapor Deposition) involving complex chemical processing or vacuum-based equipment. This work introduces a flexible alternative method for producing ultrapure polycrystalline thin films with exceptional morphological control. The process utilizes a planetary ball-mill to wet-mill ultra-pure crystalline ingot into colloidal nanocrystals (NC), followed by rapid deposition in a centrifuge to form a compact, thin film across a silicon substrate. Laser sintering is then used to rapidly form a continuous denser film with excellent substrate adhesion and unique control of the morphological properties. This work demonstrates a new method using laser sintering that can form a 1.5 μm thin film of PbSe with equivalent physical and electrical (p-type with a carrier concentration of 4.5 × 10 17 /cm 3 and resistivity value of 0.17 Ωcm) properties to CBD/PVD. The results are presented for the process development, film morphology, crystal structure, and electrical properties. Lastly, unlike traditional deposition methods, this alternative process is environmentally responsible by producing zero hazardous waste by allowing recovery of all unused PbSe for reuse. The reported method is applicable for achieving thin films from a variety of high purity bulk materials. • New methods for reducing hazardous materials in microelectronics and sensors. • Rapid and tailorable way to deposit polycrystalline thin films. • Performance of infrared sensors has room to improve. • Combine deposition and patterning in one laser sintering step. • Insitu-doping of thin films.

Jang M., Hoglund E.R., Litwin P.M., Yoo S., McDonnell S.J., Howe J.M., Gupta M.C.

Photoconductive PbSe thin films are highly important for mid-infrared imaging applications. However, the photoconductive mechanism is not well understood so far. Here we provide additional insight on the photoconductivity mechanism using transmission electron microscopy, x-ray photoelectron microscopy, and electrical characterizations. Polycrystalline PbSe thin films were deposited by a chemical bath deposition method. Potassium iodide (KI) was added during the deposition process to improve the photoresponse. Oxidation and iodization were performed to sensitize the thin films. The temperature-dependence Hall effect results show that a strong hole–phonon interaction occurs in oxidized PbSe with KI. It indicates that about half the holes are trapped by KI-induced self-trapped hole centers (Vk center), which results in increasing dark resistance. The photo Hall effect results show that the hole concentration increases significantly under light exposure in sensitized PbSe, which indicates the photogenerated electrons are compensated by trapped holes. The presence of KI in the PbSe grains was confirmed by I 3d5/2 core-level x-ray photoelectron spectra. The energy dispersive x-ray spectra obtained in the scanning transmission electron microscope show the incorporation of iodine during the iodization process on the top of PbSe grains, which can create an iodine-incorporated PbSe outer shell. The iodine-incorporated PbSe releases electrons to recombine with holes in the PbSe layer so that the resistance of sensitized PbSe is about 800 times higher than that of PbSe without the iodine-incorporated layer. In addition, oxygen found in the outer shell of PbSe can act as an electron trap. Therefore, the photoresponse of sensitized PbSe is from the difference between the high dark resistance (by KI addition and iodine incorporation) and the low resistance after IR exposure due to electron compensation (by electron traps at grain boundary and electron–hole recombination in KI hole traps).

Chatterjee A., Balakrishnan J., Pendyala N.B., Koteswara Rao K.S.

This paper reports development and performance evaluation of room temperature operated Mercury Cadmium Telluride (HgCdTe) colloidal quantum dot (CQD) coated Si Readout Integrated Circuit (ROIC) based Infrared (IR) Focal Plane Array (FPA). HgCdTe CQD has been synthesized through bottom up chemical approach and coated over commercially off-the-shelf (COTS) Si ROIC die using indigenously developed Shock Wave Dispersion Technique to achieve better uniformity, thickness control and adhesion to Si ROIC compared to spin coating or drop casting, better absorption of photons which resulted in improved imaging performance. Images of various IR and visible targets have been captured and performance analysis has been carried out and detectivity of 4.8 × 10 7 Jones achieved at room temperature for IRFPA fabricated by new material deposition technique. Temperature dependent photo-response variation of the IR FPA also has been evaluated to determine optimum operating temperature.

Jang M., Kramer M.T., Yoo S., Gupta M.C.

PbSe thin films were deposited on SiO2/Si wafers using chemical bath deposition for mid-wave infrared (MWIR) detection. To enhance the photosensitivity of PbSe thin films, oxidation, followed by iodization, was performed to create a PbI2/PbSe two-layer system for efficient MWIR detection in the spectral range from 3 µm to 5 µm. A near-infrared (IR) laser annealing was performed after sensitization with 1070 nm wavelength at an energy density of 1J/cm2 to selectively heat the PbSe thin films. After IR laser annealing, the change in resistance between dark condition and MWIR illumination improved significantly from 19.8% to 22.6%. In addition, the dark resistance increased by 32.5% after IR laser annealing. IR photoluminescence spectra after IR laser annealing shows an increase in the sub-peak intensities from iodine incorporation. The results indicate that more iodine is incorporated into Se sites at the outer regions of PbSe grains. Therefore, more donors (electrons) from iodine diffuse into PbSe and recombine with holes so that PbSe thin film after IR laser annealing shows much higher dark resistance. Test devices with NiCr electrodes at the bottom of PbSe were fabricated with feature sizes of 40 µm to investigate the effect of IR laser annealing on electrical properties and specific detectivity (D∗). I-V characteristics show dark resistance increased after IR laser annealing. The specific detectivity increases significantly after IR laser annealing at the applied bias of 10 V at 270 K from 0.55×1010cmHz1/2W−1 to 1.23×1010cmHz1/2W−1 due to dramatic noise reduction, which is originated from higher dark resistance.

Chatterjee A., Babu N., Rao K.S.

This paper reports development of Mid Wave Infrared (MWIR) Focal Plane Array (FPA) using chemically synthesized Mercury Cadmium Telluride (Hg1-xCdxTe) semiconductor Colloidal Quantum Dots (CQD) coated over 320×256 pixels silicon Readout Integrated Circuit (ROIC), having significant photo-response in the MWIR spectral band (λ = 2.5µm to 5.0µm) at room temperature and variation of photo-response at lower operating temperature (120K to 260K). HgCdTe CQD has been synthesized chemically. We have characterized the optical performance of the developed sensor using calibrated Black Body Source and infrared lamps along with optical high pass filter (λCutoff = 2.1 µm) to understand its response against MWIR radiation at different operating temperature as an introductory step towards development of MWIR FPA sensitive in MWIR region and determination of optimum operating condition to achieve higher specific detectivity (D*). Optical response of the indigenously developed FPA has been evaluated inside a cryostat having optical window at different temperatures lower than ambient and peak response is found to be at T=140K.

Rogalski A., Kopytko M., Martyniuk P.

In the past decade, there has been significant progress in development of the colloidal quantum dot (CQD) photodetectors. The QCD’s potential advantages include: cheap and easy fabrications, size-tunable across wide infrared spectral region, and direct coating on silicon electronics for imaging, what potentially reduces array cost and offers new modifications like flexible infrared detectors. The performance of CQD high operating temperature (HOT) photodetectors is lower in comparison with traditionally detectors existing on the global market (InGaAs, HgCdTe and type-II superlattices). In several papers their performance is compared with the semiempirical rule, “Rule 07” (specified in 2007) for P-on-n HgCdTe photodiodes. However, at present stage of technology, the fully-depleted background limited HgCdTe photodiodes can achieve the level of roomtemperature dark current considerably lower than predicted by Rule 07. In this paper, the performance of HOT CQD photodetectors is compared with that predicted for depleted P-i-N HgCdTe photodiodes. Theoretical estimations are collated with experimental data for both HgCdTe photodiodes and CQD detectors. The presented estimates provide further encouragement for achieving low-cost and high performance MWIR and LWIR HgCdTe focal plane arrays operating in HOT conditions.

Maskaeva L.N., Yurk V.M., Markov V.F., Kuznetsov M.V., Voronin V.I., Muhamediarov R.D., Zyrianov G.V.

By means of chemical bath deposition of selenourea in the presence of ammonium iodide and antioxidants (C6H8O6, Na2SO3, Na2SO3 + C6H8O6, SnCl2) high adhesion nanostructured films of PbSe with a thickness of 300–690 nm were obtained. Depending on the type of antioxidant introduced into the reaction mixture, the dimensions of the crystallites forming the PbSe film in the series listed decrease from 60 ± 10 to 8 ± 2 nm with simultaneous growth from 0.21 ± 0.01 to 1.25 ± 0.15% of microstresses. An increase in the lattice constant of as-deposited lead selenide from 0.6129(8) to 0.6265(9) nm correlates with an increase in the content of iodine in the PbSe film. Using X-ray diffraction, scanning electron microscopy with EDX-analysis and X-ray photoelectron spectroscopy, we investigated the effect of annealing PbSe films on their elemental, phase composition, lattice parameters and surface morphology. It is established that the annealed PbSe films are multiphase and contain PbSeO3, PbSeO4, PbI2. Low-temperature studies in the range of 213–333 K allowed us to determine the PbSe band gap, ranged from 0.265 to 0.349 eV, which depends strongly on a type of antioxidant. PbSe films synthesized using ascorbic acid and tin (II) chloride have anomalously high responsibility at relatively low temperatures, which makes it possible to manufacture highly sensitive IR detectors on their basis.

Shuklov I.A., Razumov V.F.

The review concerns the state of the art in methods of synthesis of colloidal lead chalcogenide quantum dots (QDs). The most recent data on the mechanisms of chemical transformations involving various precursors are discussed. Particular attention is paid to the influence of (i) trace impurities in the reactants used and (ii) post-synthesis treatment on the physicochemical properties of QDs used in photoelectric devices. The bibliography includes 129 references.

Nakotte T., Luo H., Pietryga J.

Hybrid lead chalcogenide (PbE) (E = S, Se) quantum dot (QD)-layered 2D systems are an emerging class of photodetectors with unique potential to expand the range of current technologies and easily integrate into current complementary metal-oxide-semiconductor (CMOS)-compatible architectures. Herein, we review recent advancements in hybrid PbE QD-layered 2D photodetectors and place them in the context of key findings from studies of charge transport in layered 2D materials and QD films that provide lessons to be applied to the hybrid system. Photodetectors utilizing a range of layered 2D materials including graphene and transition metal dichalcogenides sensitized with PbE QDs in various device architectures are presented. Figures of merit such as responsivity (R) and detectivity (D*) are reviewed for a multitude of devices in order to compare detector performance. Finally, a look to the future considers possible avenues for future device development, including potential new materials and device treatment/fabrication options.

Qiu J., Weng B., McDowell L.L., Shi Z.

A mid-wave infrared (MWIR) uncooled PbSe-QDs/CdS p-n heterojunction photodiode has been fabricated using a wet-chemical synthesis route. This offers a low-cost alternative to traditional monocrystalline photodiodes relying on molecular beam epitaxy (MBE) technology. It was demonstrated that the post-annealing is critical to tailor the photoresponse wavelength and to improve the performance of photodiodes. After annealing at 673 K in air for 0.5 h, the ligand-free PbSe-QDs/CdS photodiode exhibits a MWIR spectral photoresponse with a cutoff wavelength of 4.2 μm at room temperature. Under zero-bias photovoltaic mode, the peak responsivity and specific detectivity at room temperature are 0.36 ± 0.04 A W-1 and (8.5 ± 1) ×108 cm Hz1/2 W-1, respectively. Temperature-dependent spectral response shows an abnormal intensity variation at temperatures lower than 200 K. This phenomenon is attributed to the band alignment transition from type II to type I, resulting from the positive temperature coefficient of PbSe. In addition, it was proved that In doped CdSe (CdSe:In) films could be used as a promising new candidate of infrared transparent conductive electrodes, paving the way for monolithic integration of uncooled low-cost MWIR photodiodes on Si readout circuitry.

Zhu M., Liu X., Liu S., Chen C., He J., Liu W., Yang J., Gao L., Niu G., Tang J., Zhang J.

PbSe colloidal quantum dots (CQDs) are widely used in solar cells because of their tunable band gap, solution processability, and efficient multiple exciton generation effect. The most efficient PbSe CQD solar cells use high-temperature-processed ZnO as the electron transport layer (ETL), limiting their applications in flexible photovoltaics. Currently, low-temperature solution-processed SnO2 has been demonstrated as an efficient ETL for high-efficient PbS CQD and perovskite solar cells because of less parasitic light absorption and higher electron mobility. Herein, we introduce low-temperature solution-processed SnO2 as ETL for PbSe CQD solar cells, and fabricate the PbSe CQD absorber layer with a one-step spin-coating method. The champion device with the structure of FTO (SnO2:F)/SnO2/PbSe-PbI2/PbS-EDT (1,2-ethanedithiol)/Au achieves a high open-circuit voltage of 577.1 mV, a short-circuit current density of 24.87 mA cm-2, a fill factor of 67%, and an impressive power conversion efficiency of 9.67%. Our results pave the way for the development of low-temperature flexible PbSe CQD solar cells.

Fang Y., Ge Y., Wang C., Zhang H.

Ganguly S., Jang M., Tan Y., Yoo S., Gupta M.C., Ghosh A.W.

We present a physics based multiscale materials-to-systems model for polycrystalline PbSe photodetectors that connects fundamental material properties to circuit level performance metrics. From experimentally observed film structures and electrical characterization, we first develop a band structure model that explains carrier-type inversion and large carrier lifetimes in sensitized films. The unique band structure of the photosensitive film causes separation of generated carriers with holes migrating to the inverted PbSe|PbI2 interface, while electrons are trapped in the bulk of the film intergrain regions. These flows together form the 2-current theory of photoconduction that quantitatively captures the I−V relationship in these films. To capture the effect of pixel scaling and trapped carrier blocking, we develop a model for the metallic contacts with the detector films based on the relative workfunction differences. We also develop detailed models for various physical parameters such as mobility, lifetime, quantum efficiency, noise, etc. that connect the detector performance metrics such as responsivity R and specific detectivity D∗ intimately with material properties and operating conditions. A compact Verilog-A based SPICE model is developed which can be directly combined with advanced digital Read-Out Integrated Circuit cell designs to simulate and optimize high performance Focal Plane Arrays which form a critical component in the rapidly expanding market of self-driven automotive, internet of things security, and embedded applications.

Jang M., Yoo S., Kramer M.T., Dhar N.K., Gupta M.C.

Tran H., Pham T., Margetis J., Zhou Y., Dou W., Grant P.C., Grant J.M., Al-Kabi S., Sun G., Soref R.A., Tolle J., Zhang Y., Du W., Li B., Mortazavi M., et. al.

The GeSn detector offers high-performance Si-based infrared photodetectors with complementary metal-oxide-semiconductor (CMOS) technique compatibility. In this work, we report a comprehensive study...

Quanjiang Lv, Rongfan Li, Tianxi Hu, Yong Wu, Junlin Liu

Infrared focal plane array (IRFPA) detector, a key research focus in next-generation infrared detection technology, plays a crucial role in optoelectronic sensing. Here, we report the integration and reliability of a PbSe-based IRFPA employing a row-column scanning readout architecture. The design features a surface passivation layer and through-hole structures to ensure robust electrical connectivity, enhancing both stability and performance. The detector, with dimensions of 3.5 mm×3.5 mm, a pixel size of 200 μm <teshuzifu>x 100 μm, and a pixel pitch of 200 μm, demonstrates structural integrity validated by electro-thermal simulations. At room temperature, pixel-level and imaging assessments reveal an average detectivity of 9.86×10⁹ Jones and a responsivity of 1.03 A/W, with a 100% effective pixel yield. Remarkably, the device retains high stability, exhibiting only a 3.6% performance decline after 150 days of air exposure, attributed to the protective effects of the passivation layer. Infrared imaging across varied light intensities shows pronounced contrast, confirming the detector’s sensitivity to illumination gradients. These results offer critical technical insights and a theoretical framework for advancing high-performance, stable PbSe-based IRFPA detectors.

Hasnain M., Wahed A., Das J., Arkook B., Harb M., Mia N.

Abstract This study presents a comprehensive investigation and in-depth analysis of the optimization of Pb-based quantum dot solar cells (QDSCs), concentrating on the influences of doping concentration, absorber layer thickness, defect density, temperature, and resistive elements. We systematically examined three absorber materials: lead sulfide (PbS), tetrabutylammonium iodide-treated PbS (PbS-TBAI), and lead selenide (PbSe) quantum dots (QDs). Optimal doping concentrations of 1 × 10 17 cm−3 for PbS and 1 × 10 22 cm−3 for both PbS-TBAI and PbSe were identified. Our findings reveal that precise control of these parameters can significantly enhance power conversion efficiency (PCE), achieving values of 24.6%, 28%, and 26.2% for PbS, PbS-TBAI, and PbSe, respectively. Additionally, we investigated the impact of absorber layer thickness on device performance. We discovered that a 1 µm thickness for PbS yields a maximum PCE of 32.9% due to balanced photon absorption and reduced Shockley–Read–Hall recombination. Conversely, PbSe’s performance declined with increased thickness because of its layer-dependent bandgap. We found that lower defect densities ( 1 × 10 14 cm−3) critically improve PCE and fill factor across all materials. The temperature-dependent studies demonstrated that PbS-TBAI exhibits remarkable resilience, maintaining efficiency under thermal stress due to effective surface passivation. Analyses of series and shunt resistances highlighted the importance of minimizing internal resistances to optimize device performance. The proposed device structure comprises a fluorine-doped tin oxide front contact layer, a silver sulfide (Ag2S) electron transport layer, the QD absorber layer (PbS, PbS-TBAI, or PbSe), and copper(I) oxide (Cu2O) hole transport layer. Utilizing cascade band alignment, we achieved a record PCE of 32.9%. This research highlights the significant potential of Pb-based QDSCs for achieving high efficiencies through promising material and structural optimization, positioning them as competitive candidates for next-generation solar technologies. The results provide a valuable understanding of designing high-performance QDSCs, paving the way for their integration into sustainable energy solutions.

Bidney G.W., Duran J.M., Ariyawansa G., Anisimov I., Hendrickson J.R., Astratov V.N.

AbstractAnisotropic wet etching of silicon (Si) has been known for decades, but the extraordinary capabilities of this technology to provide highly ordered microphotonic arrays have received limited attention in previous studies. It is shown that these capabilities include: i) a unique self‐terminating etching nature − crucial for achieving uniform arrays over centimeter‐scale wafers, ii) an extraordinary smoothness of the slow‐etching (111) planes, and iii) a precise geometry control including the extent micropyramids or micropyramidal voids are truncated. The combination of these properties transforms this technology into a versatile platform for novel detector and emitter applications in Si photonics. The optical properties of such arrays are studied by finite‐difference time‐domain modeling in two realms represented by different boundary conditions (BCs). Periodic BCs result in Talbot self‐images experimentally observed in this work. Perfectly matched layer BCs describe mesoscale interference effects resulting in the subwavelength focusing properties of micropyramids. Enhancements in the performance of mid‐wave infrared (MWIR) focal plane arrays are demonstrated by monolithic integration of Si micropyramids with silicon‐platinum silicide Schottky barrier photodetectors. Finally, it is shown that Si micropyramidal arrays can be used to enhance light extraction and directionality of quantum sources and infrared scene projectors.

Núñez-Carrero K.C., Alonso-Pastor L.E., Herrero M.

Sohrabikia Z., Abedi Ravan B., Jafari M.

Abstract This study employs first-principle calculations within density functional theory (DFT) to explore the structural, electronic, optical, and thermoelectric properties of lead chalcogenides (PbS, PbSe, and PbTe). The investigation focuses on their potential application as infrared photodetectors, leveraging their narrow-band gap semiconductor characteristics. The influence of pressure on the band gap and various electronic, optical, and thermoelectric properties is thoroughly analyzed. The calculated band gap values for PbS, PbSe, and PbTe are determined to be 0.29 eV, 0.18 eV, and 0.18 eV, respectively, aligning well with experimental data. Notably, the study reveals non-linear changes in band gap values under pressure, with phase transitions observed at specific pressure thresholds in PbS and PbSe, but not in PbTe. Under varying pressure conditions, the optical peaks shift towards lower energy levels with increased intensity. The static dielectric constant of PbS, PbSe, and PbTe exhibits distinct variations within pressure ranges of 0–8 GPa. Transport coefficients (S, σ, ke) are calculated using semi-classical Boltzmann theory across different temperatures and pressures, indicating that heavier compounds exhibit higher electrical and thermal conductivity values. At 300 K, the maximum ZT values are determined to be 0.85, 0.8, and 0.52 for PbS, PbSe, and PbTe, respectively. The study suggests enhanced thermoelectric properties of these structures at lower temperatures, particularly highlighting PbS and PbSe as promising candidates for thermoelectric applications below 500 K. Exploring the impact of pressure on the thermoelectric parameters of lead chalcogenides reveals interesting trends, with PbTe demonstrating higher thermoelectric efficiency under increased pressure compared to PbS and PbSe. These findings provide valuable insights into the potential applications and performance of lead chalcogenides in IR detection and thermoelectric systems.

Ponomarenko Vladimir P., Popov Victor, Shuklov Ivan, Ivanov Victor V., Razumov Vladimir F.

Photosensing based on colloidal quantum dots (CQDs) is a rapidly developing area of infrared photoelectronics. The use of colloidal quantum dots markedly simplifies the manufacture, decreases the restrictions to the pixel pitch of the photosensitive elements, and reduces the production cost, which facilitates the wide use of IR sensors in various technological systems. This paper is the first exhaustive overeview of the architectures, methods of manufacturing and basic properties of photonic sensors based on colloidal quantum dots of compounds of Group II, IV and VI elements. Characteristic features of the synthesis and roles of the ligands and CQD morphology in the design of photosensors are considered in detail. The structures of photoresistive, photodiode and phototransistor elements based on HgTe, HgSe, PbS and PbSe CQDs, which are sensitive in various spectral ranges, are described. The main parameters of the most advanced optoelectronic devices based on colloidal quantum dot structures are presented. The key trends in the development of this area are analyzed.The bibliography includes 361 references.

Kim S., Choo S., Kim Y., Hwang W.S., Shin M.

Near-infrared (NIR) light is used in nondestructive spectroscopies to analyze various compounds in several applications. A PbSe nanocrystal film used in NIR detectors is fabricated using a magnetron sputtering process. The PbSe NIR detectors can be fabricated at a low cost and can operate at ambient temperatures. In this study, the surface morphology and chemical and crystal states of PbSe and its NIR detection performance are investigated and compared with existing reports in the literature. The PbSe film grown by sputtering exhibits nano- and columnar crystal structures, predominantly halite-like (100) face-centered cubic structures. The PbSe film contains PbO and SeO2 and exhibits dual-absorption band-to-band transitions at 0.43 and 0.52 eV. The sputtered PbSe film is used to fabricate an NIR photodetector with a metal-semiconductor-metal structure. The detector shows fast rise and decay times of 0.14 and 0.12 s, respectively, and responsivity of approximately 0.01 A/W under infrared illumination. Based on this study, a low-cost PbSe NIR detector that can operate at room temperature is developed for early fire detection.

Lv Q., Li R., Jiang Z., Fan L., Huang Z., Huan Z., Yu M., Liu G., Qiao G., Liu J.

In pursuit of addressing the inherent challenges associated with gas partial pressure control and non-uniform diffusion of solid iodine encountered in conventional sensitization methods, this study delves into the impact of liquid sensitization on the structural and electrical properties of lead selenide (PbSe) films. The sensitization process entails iodination of PbSe films within varying concentrations of potassium iodide (KI) solutions, followed by high-temperature sensitization. The phase composition, surface morphologies, carrier concentration and mobility, and detectivity of the PbSe films after sensitization were investigated systematically. Our findings illuminate the transformative potential of liquid iodine sensitization in the modification of the crystal boundary barrier within PbSe films, thereby engendering substantial enhancements in both structural and electrical attributes. Iodine assumes a pivotal role in the orchestration of this boundary barrier modulation, which, in turn, has birthed an innovative methodology for crafting high-performance PbSe photodetectors. Remarkably, when films were sensitized with a KI concentration of 0.05 M, the maximum detectivity achieved reached an impressive 2.27 × 109 Jones. This study not only deepens our understanding of the underlying mechanisms responsible for the optoelectronic response of PbSe films but also underscores the immense potential of liquid iodine sensitization as a promising way for elevating their overall performance.

Schwanninger R., Nashashibi S., Yarema O., Koepfli S.M., Fedoryshyn Y., Wood V., Leuthold J.

AbstractHighly responsive, low noise, and inexpensive photodetectors that operate in the mid‐infrared (MIR) wavelength regime are in high demand for applications ranging from fundamental science to large scale industries. However, simultaneously achieving all this in one device architecture is very challenging. In this work, mercury telluride (HgTe) colloidal quantum dot (cQD) based photodetectors are systematically improved by the introduction of new metamaterial designs. The new designs are found by utilizing simulations. Thereby the structures are optimized to increase the responsivity and simultaneously decrease the noise spectral current density. This is achieved by focusing on improving the photogenerated charge carrier collection efficiency while reducing the active material volume without altering the near unity absorption. A standard metamaterial perfect absorber architecture based on disc resonators is used as a starting point for the optimization process. By optimizing the carrier extraction through contact engineering, resulting in a narrow slot metamaterial, an overall ≈13‐fold responsivity and ≈345‐fold detectivity increase is achieved. The final metamaterial design reaches a responsivity of 16.2 A W−1 and detectivity of 6×108 Jones at a wavelength of 2710 nm. The analysis therefore provides a route to improve the responsivity and noise characteristics of mid‐infrared photodetectors based on cost‐efficient colloidal quantum dots.

Su L., Liu Y., Zhang H., Yang Y., Qiu J.

Abstract A novel uncooled mid-wavelength infrared (MWIR) P+pBn+ barrier detector based on epitaxial PbSe absorber layer on Ge substrate is theoretically investigated by finite element analysis in order to achieve optimal detection performance. The simulated results show that the P+pBn+ barrier architecture can further effectively reduce the room-temperature dark current to 4.45 mA cm−2 under −0.1 V bias, which is 12 times lower than a PbSe pBn+ unipolar barrier device in a previous study. Moreover, the P+pBn+ barrier architecture exhibits excellent responsivity and detectivity of 1.83 A W −1 and 3.23 × 1010 cm Hz1/2 W−1 at 3.8 μm, respectively. These results suggest that this P+pBn+ barrier detector based on natural MBE epitaxy technology could have potential in the emerging high-sensitivity and high-detectivity uncooled MWIR applications.

Olkhova A.A., Omelchenko P.P., Shulga B.G., Patrikeeva A.A., Dubkova M.A., Sergeev M.M.

Features of PbSe chalcogenide films modified by irradiating with nanosecond laser pulses in various modes of treatment in an oxygen-free environment are studied. Changes in optical properties of the films after laser irradiation and modification of their structure in a nitrogen atmosphere were examined. It is shown that the presence of a nitrogen medium does not significantly affect the optical characteristics of the films obtained as a result of laser modification with an incident radiation wavelength of 1064 nm. These results indicate that the use of an oxygen-free medium in the modifying sensitive detectors is not needed. The obtained experimental data are the basis for expanding the knowledge on laser modification of the structure of semiconductor chalcogenide films and revealing the relationship between the optical characteristics of the material before and after laser exposure. The results of the study can be used in applied problems related to the manufacture of photodetectors in devices for gas and bioanalysis, photovoltaics, and optoelectronics.

Harrison J.T., Gupta M.C.

The motivation of this work is to demonstrate the versatility and potential of laser processing in the fabrication of PbSe thin films and focal plane array devices. This work fabricates an FPA device with any need for the suite of equipment and chemicals necessary for photolithography and etching. Advances in laser technologies and the vast number of laser parameters available are enabling the huge potential for laser processing of thin films and device fabrication. This can be accomplished faster using lasers with fewer steps than using conventional thin film deposition and photolithography methods. This work presents the fabrication and simple operation of a proof-of-concept PbSe-based, 120-pixel PFA (10 x 12 pixel) focal plane array using only laser processing for film deposition and device patterning. Lasers were used to both deposition and pattern a PbSe film with 60 x 70 µm pixels with 100 µm pitch with a unit cell photoresponse of 17% DelR. Additional results, challenges, limitations, and suggested future improvements are presented.

Fu Y., Zhang G., Tang H., Yang Y., Qiu J.

Enhancing the detectivity is still a challenge for uncooled mid-infrared PbSe photoconductive (PC) detectors. Antireflection coating (ARC) provides a convenient solution to this challenge. Herein, antireflection physical modeling was proposed based on microstructural features of PbSe PC detectors. The simulated results show that the surface roughness contributes to the absorption enhancement of PbSe detectors, which reflects the advantage of the chemical bath deposition (CBD) manufacturing technology. Meanwhile, being the optimal ARC choice, ZnS ARC with thickness from 300 to 420 nm could induce more than 20 % absorption improvements in coarse CBD-PbSe films, which is confirmed by a signal enhancement from CBD-PbSe PC detectors covered with ZnS ARC. Combing with a noise reduction, the peak detectivity (D*) is almost doubled from 0.8 × 1010 to 1.5 × 1010 cm‧Hz1/2‧W−1 after depositing a desired ZnS ARC. Furthermore, ZnS ARC significantly eliminates the performance degradation of detectors triggered by moisture in the air. The low-cost ZnS ARC with good repeatability, which combines the characteristics of antireflection and passivation, provides an available solution to promote the industrialization of PbSe PC detectors.

Al Mahfuz M.M., Islam R., Zhang Y., Baek J., Park J., Lee S., Ko D.

Metal chalcogenide thin films are used in a wide range of modern technological applications. While vacuum deposition methods are commonly utilized to fabricate the film, solution-based approaches have garnered an increasing interest due to their potential for low-cost, high-throughput manufacturing, and compatibility with silicon complementary metal–oxide–semiconductor processing. Here, we report a general strategy for preparing mid-wavelength infrared (MWIR = 3–5 μm) photoconductive film using a PbSe molecular ink. This ethylenediamine-based ink solution is synthesized using a simple diphenyl dichalcogenide route, and the deposited film, after the sensitization annealing, exhibits a specific detectivity of 109 Jones at 3.5 μm at room temperature. This work represents the demonstration of MWIR-photosensitive semiconductor films prepared using an emerging alkahest-based approach, highlighting a significant research avenue in the pursuit toward low SWAP-C (size, weight, power consumption, and cost) infrared imager development.

Su L., Liu Y., Lu H., Zhang H., Yang Y., Qiu J.

Abstract Mid- and long-wavelength IR photodetectors incorporating narrow-bandgap semiconductors often face the challenge of large RT dark current, limiting their applications in military and civilian use. Herein, a novel pBn+ barrier detector architecture based on a lead selenide/indium selenide barrier structure is proposed to significantly suppress the dark current, so that uncooled mid-wave IR (MWIR) photodetectors with high performance can be achieved. The finite element analysis of the detector demonstrates reduced RT dark current down to 55 mA cm−2 under −0.1 V bias, which is a two-fold decrease compared to the InAs/InAsAb type-II superlattice detector. In addition, at RT, the optimized pBn+ barrier detector exhibits excellent responsivity and detectivity of 1.23 A W−1 and 9.47 × 109 cm Hz1/2·W−1 at 3.8 μm, respectively. The PbSe-based barrier architecture provides a promising industrialization solution for high-performance uncooled MWIR photodetectors.