Low Dark Current Density Research Articles

Ultralow Dark Current Room‐Temperature Infrared Photodetector Based on InSb Nanosheets/MoS2 Van der Waals Heterostructure

As a narrow‐bandgap semiconductor, InSb is widely used in infrared (IR) detection due to its excellent performance and other characteristics such as ultrahigh electron mobility, extremely high quantum efficiency, and robust chemical properties. Herein, an ultralow dark current room‐temperature IR photodetector based on InSb nanosheets (NSs)/MoS2 flakes van der Waals (vdW) heterostructure is presented. Benefiting from a large surface‐to‐volume ratio and phonon scattering suppressed on the nanostructure, InSb NSs devices have high photosensitivity and low dark current density (16.67 A cm−2). To further suppress the dark current, a vdW heterojunction composed of InSb NSs and MoS2 is fabricated. When the InSb NSs/MoS2 vdW heterostructures’ photodetector work on a photovoltaic model (zero‐bias operation), the device shows a dark current density as low as 0.12 A cm−2 at room temperature, exhibiting a high external quantum efficiency (EQE) of 3.6 × 102%, the responsivity of 3.8 A W−1, and detectivity of 1.2 × 109 cm Hz1/2 W−1 under 1310 nm laser illumination. These results demonstrate that InSb NSs vdW heterostructure is a feasible scheme to realize InSb room‐temperature IR detection.

Effective passivation via additive engineering based on CsPbBr3 films photodetectors and image sensor application

All-inorganic perovskite photodetectors aroused widespread attention due to the splendid photoelectric characteristics and stability. However, the inherent defects in perovskite films hinders the progress of the photodetectors. Here, a Lewis base of thioacetamide additive was used to passivate defects in CsPbBr3 perovskite films based on Lewis acid-base interactions. The quality of the film has been distinctly enhanced due to the interaction between the S donor in thioacetamide and the uncoordinated Pb2+ in perovskite, diminishing the defect state density and inhibits the non-radiative recombination. The self-powered champion device based on CsPbBr3 film contain optimum thioacetamide additive exhibits a lower dark current density of 4.01 nA/cm2, a peak responsivity of 0.39 A/W, a rapid rise/decay time of 12.4 μs/56.2 μs, a peak detectivity of 1.08 × 1013 Jones and a lager linear dynamic range of 99 dB, which are much better than photodetector based on CsPbBr3 perovskite without TAA additive. Furthermore, it exhibits high-resolution imaging sensing capability at zero bias. This research affords guidance for the performance improvement and application of all-inorganic perovskite photodetectors.

A Route toward High-Detectivity and Low-Cost Short-Wave Infrared Photodetection: GeSn/Ge Multiple-Quantum-Well Photodetectors with a Dielectric Nanohole Array Metasurface.

High-detectivity and low-cost short-wave infrared photodetectors with complementary metal-oxide-semiconductor (CMOS) compatibility are attractive for various applications such as next-generation optical communication, LiDAR, and molecular sensing. Here, GeSn/Ge multiple-quantum-well (MQW) photodetectors with a dielectric nanohole array metasurface were proposed to realize high-detectivity and low-cost SWIR photodetection. The Ge nanohole array metasurface was utilized to enhance the light absorption in the GeSn/Ge MQW active layer. Compared with metallic nanostructures, the dielectric nanohole structure has the advantages of low intrinsic loss and CMOS compatibility. The introduction of metasurface architecture facilitates a 10.5 times enhanced responsivity of 0.232 A/W at 2 μm wavelength while slightly sacrificing the dark current density. Besides, the metasurface GeSn/Ge MQW photodetectors benefit 35% improvement in the 3 dB bandwidth compared to control GeSn/Ge MQW photodetectors, which can be attributed to the reduced RC delay. Due to the high responsivity and low dark current density, the room temperature specific detectivity at 2 μm is as high as 5.34 × 109 cm·Hz1/2/W, which is the highest among GeSn photodetectors and is better than commercial InSb and PbSe photodetectors operating at the similar wavelength. This work offers a promising approach for achieving low-cost and effective photodetection at 2 μm, contributing to the development of the 2 μm communication band.

Growth and Dark Current Analysis of GaSb- and InP-Based Metamorphic In0.8Ga0.2As Photodetectors.

Short-wavelength infrared photodetectors based on metamorphic InGaAs grown on GaSb substrates and InP substrates are demonstrated. The devices have a pBn structure that employs an AlGaAsSb thin layer as the electron barrier to suppress dark current density. The strain effect on the electrical performance of the devices was specifically studied through the growth of the pBn structure on different substrates, e.g., InP and GaSb, via a specific buffering technique to optimize material properties and minimize dark current. A lower device dark current density, down to 1 × 10-2 A/cm2 at room temperature (295 K), was achieved for the devices grown on the GaSb substrate compared to that of the devices on the InP substrate (8.6 × 10-2 A/cm2). The improved properties of the high-In component InGaAs layer and the AlGaAsSb electron barrier give rise to the low dark current of the photodetector device.

Gradient 2D–3D Ruddlesden-Popper perovskite film for high-performance self-powered photodetectors

Quasi-2D Ruddlesden–Popper perovskites have been widely used in the photoelectric detection field owing to their tunable optical bandgap and superior stability. However, because phases formed in the quasi-2D perovskite films have unfixed n values, the transport channels of charge carriers are greatly disordered. Herein, based on the hot-casting method, the effects of substrate temperature on the surface morphology and internal phases distribution of 2D perovskite films was investigated, leading to the preparation of uniform and compact 2D–3D gradient perovskite thin films. Perovskites have an orderly gradient phase distribution along the longitudinal direction of the thin film, which is beneficial to the separation and transport of carriers, thus improving the photosensitivity of photodiode over the whole visible spectrum range. The ideal photodetector fabricated at 120 ℃ has an extremely low dark current density (2.3 × 10−11A/cm2), large specific detectivity (1.22 × 1014 Jones) at 455 nm, ultra-fast response time (5.5/4.7 µs) and ultra-high on/off ratio of 108, indicating its great potential for high-efficiency photodetection without the voltage bias (0 V). Moreover, compared with 3D perovskite devices, hot-casted 2D perovskite devices exhibit greatly improved stability, with JD remaining at about 10−11A/cm2 for 400 h, which is very significant for realizing outstanding performance and stable photodiodes.

Low Dark Current Operation in InAs/GaAs(111)A Infrared Photodetectors: Role of Misfit Dislocations at the Interface.

We demonstrate an extended short-wave infrared (e-SWIR) photodetector composed of an InAs/GaAs(111)A heterostructure with interface misfit dislocations. The layer structure of the photodetector consists simply of an n-InAs optical absorption layer directly grown with a thin undoped-GaAs spacer layer on n-GaAs by molecular beam epitaxy. The lattice mismatch was abruptly relaxed by forming a misfit dislocation network at the initial stage of the InAs growth. We found high-density threading dislocations (1.5 × 109 cm-2) in the InAs layer. The current-voltage characteristics of the photodetector at 77 K had a very low dark current density (<1 × 10-9 A cm-2) at a positive applied voltage (electrons flow from n-GaAs to n-InAs) of up to ∼+1 V. Simulation of the band structure revealed that the direct connection of GaAs and InAs and the formation of interfacial states by the misfit dislocations play significant positive roles in suppressing dark current. Under illumination with e-SWIR light at 77 K, a clear photocurrent signal was observed with a 2.6 μm cutoff wavelength, which is consistent with the bandgap of InAs. We also demonstrated e-SWIR detection at room temperature with a 3.2 μm cutoff wavelength. The maximum detectivity at 294 K exceeds 2 × 108 cm Hz0.5 W-1 for the detection of e-SWIR light at 2 μm.

Driving up the quality of metal organic chemical vapor deposition-grown epitaxial wafers for highly innovative photonic applications

Quantum cascade lasers (QCL) and extended InGaAs photodetectors (ex-PDs) (operating in regime 1.9–2.6 µm wavelength) are very attractive materials for use in sophisticated photonics and microelectronics such as optical recording, scanners, laser spectroscopy, thermal or gas sensing. Once a laboratory curiosity, QCLs and ex-PDs are now becoming commercially available products, shaping exciting applications. In this work, we present the intricacies and challenges of the development and industrial production of Metal Organic Chemical Vapor Deposition (MOCVD)-grown QCL and ex-PD structures as well as demonstrate their viability for large-scale manufacturing.Different types of epitaxial structures were grown using a multi-wafer production MOCVD system, in 12 × 3″ wafer configuration per growth run. Structural and electrical properties of epitaxial layers were carefully examined.MOCVD growing of QCL and ex-PD structures is a very demanding process. MOCVD production reactor enables development of highly complicated chemical reactions, however, as gas residence is much longer than in small R&D systems, the hetero-interfaces of InGaAs/InAlAs are inevitably graded, which negatively impacts optical and electrical parameters of QCL devices. In addition, QCL structure requires the exact layer thickness as well as absolute precision and repeatability when developing strained InAlAs and InGaAs epi‑layers. In the case of ex-PDs fabrication, the crucial thing is to develop a specially designed and graded buffer layer, and to avoid numerous misfit defects and anomalies in dark current. We obtained high crystallographic quality and repeatability of the epi‑layers, which resulted in QCL high-performance continuous-wave operation and fabrication of ex-PDs with low dark current density (less than 1 × 10−4 A/cm2 at -100 mV/room temperature (RT)) achieving results consistent with Rule07 and higher quantum efficiency.

High-mobility organic semiconducting crystal for direct X-ray detection

Tissue-equivalent pure organic semiconducting crystals (OSCs) have unique advantages in direct X-ray detectors (DXDs), especially for biological tissue fluoroscopy, but their low carrier mobility and inherent weak absorption restrict the limit-of-detection (LoD) and sensitivity of DXDs. High-mobility OSCs theoretically facilitate charge collection and performance leaps, however, they are rare and suffer from poor solubility due to high conjugation, leading to nearly impossible crystal growth from solution and subsequent device applications. Here we report an ingenious solution-processed crystal-growth and high-performance DXD using 2,6-diphenylanthracene (2,6-DPA), a high-mobility OSC we developed recently. In contrast to previous OSCs, high-mobility 2,6-DPA exhibits low dark current density and large photoconductive gain, resulting in record-breaking LoD of <85 nGyair s−1 and sensitivity of >103 μC Gyair−1 cm−2. Compared with semiconductors containing high-Z atoms (Z is atomic number), the accuracy of 2,6-DPA based DXDs is not affected by near-edge absorption effects. Moreover, the non-linear relationship between irradiation current and dose rate is confirmed as a high injection effect. High mobility and ingenious crystal growth strategy make 2,6-DPA an ideal active material for DXDs and also provide the possibility for more optoelectronic applications.

Recent Progress in III–V Photodetectors Grown on Silicon

An efficient photodetector (PD) is a key component in silicon-based photonic integrated circuits (PICs). III–V PDs with low dark current density, large bandwidth, and wide operation wavelength range have become increasingly important for Si photonics in various applications. Monolithic integration of III–V PDs on Si by direct heteroepitaxy exhibits the lowest cost, the largest integration density, and the highest throughput. As the research of integrating III–V lasers on Si flourishes in the last decade, various types of III–V PDs on Si with different device structures and absorption materials have also been developed. While the integration of III–V lasers on Si using various technologies has been systematically reviewed, there are few reviews of integrating III–V PDs on Si. In this article, we review the most recent advances in III–V PDs directly grown on Si using two different epitaxial techniques: blanket heteroepitaxy and selective heteroepitaxy.

The Influence of Dimensionality on the Charge‐Density‐Wave Transition and its Application on Mid‐Infrared Photodetection

Abstract2D charge density wave (CDW) materials receive much attention for high responsivity and broadband photodetection in recent years due to their collective electron transport and narrow bandgap. However, the high dark current density problem hinders their real application. Here, a sharp CDW transition in quasi‐1D (TaSe4)2I is reported and applied for broadband photodetection. Especially at mid‐infrared region, the device shows both high photo responsivity of 1.18 ×103 A W−1 and large light on/off ratio of 80, which is superior to 2D CDW TaS2 and most reported low‐dimensional materials. Such high performance relies on two aspects. One is the much lower dark current density resulting from the pseudo gap associated with 1D Luttinger liquid state, which is supported by finite size scaling of nonlinear I–V at variable temperatures and occurrence of 1D structural phase transition consolidated by in situ Raman spectroscopy. The other is the high photocurrent associated with the “Fröhlich superconductivity” state, manifested by an ultrasensitive switching, which can be only accessible in 1D CDW materials, in agreement with the authors’ density functional theory calculation. This work thus reveals the pivotal role of dimensionality in CDW phase transition and paves a way for implementing highly sensitive broadband photodetector.

Effects of doping and minority carrier lifetime on mid-wave infrared InGaAs/InAsSb superlattice nBn detector performance

The effect of majority carrier concentration and minority carrier lifetime on the performance of mid-wave infrared ( λ cutoff = 5.5 μ m ) nBn detectors with variably doped InGaAs/InAsSb type-II superlattice absorbers is investigated. The detector layer structures are grown by molecular beam epitaxy such that their absorbing layers are either undoped, uniformly doped with a target density of 4 × 1015 cm−3, or doped with a graded profile, and variable-area mesa detector arrays are fabricated. Each material's temperature-dependent minority carrier lifetime is determined by time-resolved photoluminescence, and majority carrier concentration is extracted from capacitance–voltage measurements. Detector performance is evaluated with dark current and photocurrent measurements, from which quantum efficiency and shot-noise-limited noise-equivalent irradiance are calculated. The two doped detectors have lower dark current densities compared to their undoped counterpart due to the reduction in diffusion current as well as suppression of depletion current. Although both intentionally doped devices exhibit lower minority carrier lifetimes relative to the undoped device, the device with graded doping maintains a comparable quantum efficiency to the undoped device. Ultimately, the graded doping structure exhibits the highest sensitivity with a shot noise-limited noise-equivalent irradiance of 6.3 × 1010 photons/cm2 s in low-background light conditions, within a factor of 4× of an infrared detector pixel with Rule 07 dark current density and unity quantum efficiency. A detailed analysis of the dark current, quantum efficiency, and minority carrier lifetime provides insight into the material and device design factors that must be considered to realize a device with optimal sensitivity.

An n-Type All-Fused-Ring Molecule with Photoresponse to 1000nm for Highly Sensitive Near-Infrared Photodetector.

Most of all-fused-ring π-conjugated molecules have wide or medium bandgap and show photo response in the visible range. In this work, an all-fused-ring n-type molecule, which exhibits an ultrasmall optical bandgap of 1.22eV and strong near-infrared (NIR) absorption with an onset absorption wavelength of 1013nm is reported. The molecule consists of 14 aromatic rings and has electron donor-acceptor characteristics. It exhibits excellent n-type properties with low-lying HOMO/LUMO energy levels of -5.48eV/-3.95 eV and high electron mobility of 7.0×10-4 cm2 V-1 s-1 . Most importantly, its thin film exhibits a low trap density of 5.55×1016 cm-3 because of the fixed molecular conformation and consequently low conformation disorder. As a result, organic photodetector (OPD) based on the compound exhibits a remarkably low dark current density (Jd ) of 2.01×10-10 Acm-2 at 0V. The device shows a shot-noise-limited specific detectivity (Dsh *) of exceeding 1013 Jones at 400-1000nm wavelength region with a peak specific detectivity of 4.65×1013 Jones at 880nm. This performance is among the best reported for self-powered NIR OPDs.

Breaking the Size Limitation of Directly-Synthesized PbS Quantum Dot Inks Toward Efficient Short-wavelength Infrared Optoelectronic Applications.

PbS quantum dots (QDs) are promising building blocks for solution-processed short-wavelength infrared (SWIR) devices. The recently developed direct synthesis of semi-conductive PbS QD inks has substantially simplified the preparation processing and reduced the material cost, while facing the challenge to synthesize large-size QDs with absorption covering the SWIR region. Herein, we for the first time realize a low-cost, scalable synthesis of SWIR PbS QD inks after an extensive investigation of the reaction kinetics. Finally, based on these PbS SWIR QD inks, the solar cell demonstrates a record-high power conversion efficiency (PCE) of 1.44 % through an 1100 nm cutoff silicon filter and the photodetector device shows a low dark current density of 2×10-6 A cm-2 at -0.8 V reverse bias with a high external quantum efficiency (EQE) of 70 % at ≈1300 nm. Our results realize the direct synthesis of low-cost and scalable SWIR QD inks and may accelerate the industrialization of consumer SWIR technologies.

Breaking the Size Limitation of Directly‐Synthesized PbS Quantum Dot Inks Toward Efficient Short‐wavelength Infrared Optoelectronic Applications

AbstractPbS quantum dots (QDs) are promising building blocks for solution‐processed short‐wavelength infrared (SWIR) devices. The recently developed direct synthesis of semi‐conductive PbS QD inks has substantially simplified the preparation processing and reduced the material cost, while facing the challenge to synthesize large‐size QDs with absorption covering the SWIR region. Herein, we for the first time realize a low‐cost, scalable synthesis of SWIR PbS QD inks after an extensive investigation of the reaction kinetics. Finally, based on these PbS SWIR QD inks, the solar cell demonstrates a record‐high power conversion efficiency (PCE) of 1.44 % through an 1100 nm cutoff silicon filter and the photodetector device shows a low dark current density of 2×10−6 A cm−2 at −0.8 V reverse bias with a high external quantum efficiency (EQE) of 70 % at ≈1300 nm. Our results realize the direct synthesis of low‐cost and scalable SWIR QD inks and may accelerate the industrialization of consumer SWIR technologies.

Low-temperature spatial atomic layer deposited Ga2O3 films for high-performance flexible deep ultraviolet photodetector

This research aims to prepare amorphous gallium oxide (α-Ga2O3) films for use in flexible deep ultraviolet photodetectors. The films are deposited using high-speed spatial atomic layer deposition (SALD) at different substrate temperatures. The experimental results show that the saturating deposition rate at 145–155 °C is four to sixteen times higher than that of temporal ALD. Moreover, under the saturated SALD conditions the deposited film has less carbon impurities, oxygen-related defects, and greater compactness than under non-saturated conditions. Finally, a high-performance flexible deep ultraviolet α-Ga2O3 photodetector with fast decay time of 161 µs and low dark current density of 6.8 × 10-10 A/cm2 is achieved.

MAPb(Br1–xClx)3 Hybrid Perovskite Materials for Direct X-ray Detection

The study and development in recent years of hybrid (organic–inorganic) halide perovskite materials have given them an unprecedented opportunity for direct ionizing radiation detection, given their large attenuation coefficient and sufficient charge carrier mobility lifetime product. The use of single crystals, considered as model materials, allows us to investigate their intrinsic properties. Characterizations under X-ray illumination of detector devices based on methylammonium lead tribromide (MAPbBr3) single crystals, obtained by optimized growths, show good sensitivity but high dark current density. To improve this critical parameter, while using MAPbBr3 as the base material, we employ anion engineering within the halide elements. We present here mixed halide perovskite crystals, with bromide partially replaced with chloride, obtained through optimized growths using modified inverse temperature crystallization in dimethylformamide, leading to high-quality single crystals of the general formula MAPb(Br1–xClx)3. Six chlorine contents are targeted and carefully determined experimentally via energy-dispersive X-ray analysis and X-ray powder diffraction. For each composition, several crystals are synthesized and used to prepare X-ray detection devices. Their optoelectronic properties are determined under standard X-ray medical conditions and hint at the existence of an optimal composition. MAPb(Br0.85Cl0.15)3 exhibits the best sensitivity with a value of S ≈ 3 μC mGyair–1 cm–2 for RQA5 spectral quality and the lowest dark current density with a value of Jdark ≈ 22 nA mm–2, both recorded at a 50 V mm–1 electric field. This sensitivity value doubles our own MAPbBr3 single crystal device and is higher than that of CsI(Tl)- or a-Se-based flat panels. The present work broadens the benefits and drawbacks of employing halide engineering in perovskite materials to improve the optoelectronic performance under high-energy radiation.

High-Performance Colloidal Quantum Dot Photodiodes via Suppressing Interface Defects.

PbS colloidal quantum dot (CQD) infrared photodiodes have attracted wide attention due to the prospect of developing cost-effective infrared imaging technology. Presently, ZnO films are widely used as the electron transport layer (ETL) of PbS CQDs infrared photodiodes. However, ZnO-based devices still suffer from the problems of large dark current and low repeatability, which are caused by the low crystallinity and sensitive surface of ZnO films. Here, we effectively optimized the device performance of PbS CQDs infrared photodiode via diminishing the influence of adsorbed H2O at the ZnO/PbS CQDs interface. The polar (002) ZnO crystal plane showed much higher adsorption energy of H2O molecules compared with other nonpolar planes, which could reduce the interface defects induced by detrimentally adsorbed H2O. Based on the sputtering method, we obtained the [002]-oriented and high-crystallinity ZnO ETL and effectively suppressed the adsorption of detrimental H2O molecules. The prepared PbS CQDs infrared photodiode with the sputtered ZnO ETL demonstrated lower dark current density, higher external quantum efficiency, and faster photoresponse compared with the sol-gel ZnO device. Simulation results further unveiled the relationship between interface defects and device dark current. Finally, a high-performance sputtered ZnO/PbS CQDs device was obtained with a specific detectivity of 2.15 × 1012 Jones at -3 dB bandwidth (94.6 kHz).

Vertical‐type 3D/Quasi‐2D n‐p Heterojunction Perovskite Photodetector

AbstractThis research demonstrates a state‐of‐the‐art vertical‐transport photodetector with an n‐type 3D MAPbI3/p‐type quasi‐2D (Q‐2D) BA2MA2Pb3I10 perovskite heterojunction. This structure introduces a ≈0.6 V built‐in electric field at the n‐p junction that greatly improves the characteristics of the perovskite photodetector, and the presence of Q‐2D perovskite on the surface improves the life. The electrical polarities of the 3D and the Q‐2D perovskite layers are simply controlled by self‐constituent doping, making clearly defined n‐p characteristics. Doctor‐blade coating is used to fabricate the photodetector with a large area. The Q‐2D materials with highly oriented (040) Q‐2D (n = 2,3) planes are near the surface, and the (111) preferred planes mixed with high index Q‐2D materials (n = 4,5) are found near the 3D/Q‐2D interface. The stacking and interface are beneficial for carrier extraction and transport, yielding an external quantum efficiency of 77.9%, a carrier lifetime long as 295.7 ns, and a responsibility of 0.41 A W−1. A low dark current density of 6.2 × 10−7 mA cm−2 and a high detectivity of 2.82 × 1013 Jones are obtained. Rise time and fall time are fast as 1.33 and 10.1 µs, respectively. The results show the application potential of 3D/Q‐2D n‐p junction perovskite photodetectors.

High performance InAs0.91Sb0.09 MWIR detectors with an AlAs1-ySby graded barrier

InAs0.91Sb0.09 barrier detectors are an important candidate in realizing high operating temperature middle wavelength infrared (MWIR) photodetectors. Here, an AlAs1-ySby graded barrier layer with linear Sb composition varying from y = 1 to 0.92 is utilized to improve the extraction of photo-generated minority carriers from an InAs0.91Sb0.09 absorber layer. With the modification of valance band misalignment between the absorber and barrier layers, although a hole barrier between AlAs0.08Sb0.92 and InAs0.91Sb0.09 layers exists, the photo-generated holes can be effectively extracted. At 150 K and under zero bias voltage, the maximum quantum efficiency of the devices with a graded barrier reaches ∼56 %, which is much higher than that of the device with a uniform AlAs0.08Sb0.92 barrier. Benefiting from the low dark current density at small reverse bias voltages, a maximum specific detectivity (D*) ∼6.19 × 1011 cm⋅Hz1/2/W is realized at zero bias voltage, which is 50 % higher than the maximum D* ∼4.26 × 1011 cm⋅Hz1/2/W of the uniform barrier device operated at −150 mV bias voltage.

Solution‐Processed AgSbS2 Thin Films for Photodetection

AbstractTernary chalcogenide, silver antimony sulfide (AgSbS2), has emerged with great potential for optoelectronic applications, thanks to its excellent optical properties, facile processability and superior stability. However, high‐performance AgSbS2‐based photodiodes have not been realized mainly due to the large dark current caused by the poor morphology and device leakage. Here, compact AgSbS2 and porous AgSbS2 thin films are fabricated mainly via modulating the sol–gel processes of the precursors. After optimizing the Ag content and the thermal annealing temperature of the AgSbS2 films, AgSbS2 photodiodes with excellent performance metrics, including low dark current density, decent specific detectivity, and superior stability, are achieved. Furthermore, the optimized AgSbS2‐based photodetectors are also introduced for heart rate detection, which exhibit excellent sensitivity and great potential for real applications.