Photoconductive Detectors Research Articles

Sulfuration-induced enhancement of photodetection performance of photoconductive detector based on Bi2O2Se thin film

Significant interlayer transmission obstacles and numerous interface barriers in two-dimensional material thin films impede charge transfer, degrading device performance. However, appropriate impurity ions can enhance charge mobility by creating transfer channels and regulating interface defect states. Herein, a series of Bi2O2SxSe1-x films were prepared by a one-step hydrothermal sulfurization method. The XRD and XPS measurement and analysis can confirm that the Se atoms have been replaced by the S atoms. The introduction of S atoms can effectively enhance the number of defects in Bi2O2Se, resulting in an increase in carrier concentration, thereby improving the conductivity of Bi2O2Se film. The photoconductive detectors fabricated from these Bi2O2SxSe1-x films showed improved detection performance compared to those made from the pristine Bi2O2Se film, and the responsivity is increased by nearly 1000 times. Notably, the detector based on Bi2O2S0.37Se0.63 film has high responsivity (47.7 mA/W) and fast response time (15 ms/25 ms). The simple thin film preparation method and good device performance make it have great potential for large-scale preparation.

The Influence of Surface Treatment on the Performance of Photoconductive Detectors Based on Silicon Wafer

The Influence of Surface Treatment on the Performance of Photoconductive Detectors Based on Silicon Wafer

High-Speed 1550 nm Photoconductive Detector With Plasmonic Micro-Grating Electrodes

High-Speed 1550 nm Photoconductive Detector With Plasmonic Micro-Grating Electrodes

Accurate measurement of a THz beam radius through a knife-edge technique with a photoconductive antenna detector

In a terahertz (THz) time-domain spectroscopic system, the THz beam waist radius can be measured by eclipsing the beam waist with a semi-infinite mask while monitoring signal variation (knife-edge technique). However, the obtained beam waist radius is affected by the spatial distribution of the detector sensitivity. This effect was confirmed by calculating the refractive-index corrections required when inserting a sample into the beam waist with and without consideration of the detector sensitivity distribution and comparing them to the experimental results. The real beam waist radius was 2 times larger than that obtained by simply differentiating the signal variation in a system comprising optics symmetrical about the beam waist. This effect must be considered in obtaining the correct THz beam profile by the knife-edge technique.

Detection of optical properties of chiral substances by a photoconductive THz polarization detector

Chiral enantiomers have significant differences in biochemical functions. The use of THz wave polarization detection to characterize the optical properties of chiral substances is of great significance to the development of life science and the identification and application of chiral substances. However, the traditional polarization detection procedures of THz waves are complex, which limits the study of chiral substances. Herein, we proposed a high-sensitivity THz polarization detector, which can simultaneously obtain the change information of amplitude, phase, and polarization state through a single measurement. The optical rotation and elliptical angle of solid and liquid D/L-Glutamic acid 5-methyl ester in the THz band are studied. Then it is verified that anisotropic interference may occur in the preparation of solid samples. Finally, the effects of sample content and thickness on polarization are obtained. The experimental results show that different chirality has the opposite effect on the state of polarization, and the difference between chiral enantiomers can be detected by this method. This work is of great significance for understanding the optical properties of chiral substances and promoting the development of chiral recognition.

High-performance PbS detectors sensitized from one-step sensitization

Two-step sensitization is the key technique for achieving high-performance uncooled lead-salt infrared photoconductive detectors fabricated from vapor physic deposition (VPD) method. However, the commercialization of these devices is inhibited by the intricate sensitization processes, especially the iodination step, which requires precise control over high concentrations of iodine vapor. Herein, a one-step sensitization technique was proposed to improve the reliability of lead sulfide (PbS) detectors manufactured from VPD method. Moreover, the dependence of the detectivity on sensitization parameters involving the oxygen concentration, time, and temperature, was established and interpreted based on extensive studies on the sensitization of lead salt devices. The feasibility of the simplified sensitization was demonstrated by a room-temperature peak detectivity of 2.47 × 1010 cm Hz1/2 W−1 at 2.7 μm attained at 430 °C for 10 min in 50 % oxygen ambient. The evolution of phase, microstructure and electrical properties confirms the enhanced performance results from the improvement in PbS crystal quality as well as the formation of Pb3O2I2 and Pb2(SO4)O from high-temperature recrystallization. Therefore, the one-step sensitization paves a way for accelerating commercialization of lead-salt detectors fabricated by VPD technique.

High-responsivity, high-detectivity, broadband infrared photodetector based on MoS2/BP/MoS2 junction field-effect transistor

Sensitivity stands as a critical figure of merit in assessing the performance of a photodetector and can be characterized by two distinct parameters: responsivity or detectivity. Simultaneous optimization of these two parameters is essential to ensure the applicability of a single detector across various scenarios, yet it remains a persistent challenge for mid-infrared photodetector. Here, we demonstrate that the construction of a photoconductive detector based on a MoS2/BP/MoS2 npn junction field-effect transistor configuration can effectively balance the tradeoffs between photoresponsivity and detectivity. In this device, the black phosphorus layer serves as the channel, while the top and bottom MoS2 layers act as photogates to boost the photocurrent. Consequently, a high-performance room-temperature-operating mid-infrared photodetector with a responsivity and detectivity reaching 9.04 A W−1 and 5.36 × 109 cm Hz1/2 W−1 (1550 nm), and 7.25 A W−1 and 4.29 × 109 cm Hz1/2 W−1 (3600 nm) is achieved. Our study provides an alternative structural design, enabling the applications of mid-infrared photodetectors across multiple scenarios.

Heterojunctions of Mercury Selenide Quantum Dots and Halide Perovskites with High Lattice Matching and Their Photodetection Properties.

Heterojunction semiconductors have been extensively applied in various optoelectronic devices due to their unique carrier transport characteristics. However, it is still a challenge to construct heterojunctions based on colloidal quantum dots (CQDs) due to stress and lattice mismatch. Herein, HgSe/CsPbBrxI3-x heterojunctions with type I band alignment are acquired that are derived from minor lattice mismatch (~1.5%) via tuning the ratio of Br and I in halide perovskite. Meanwhile, HgSe CQDs with oleylamine ligands can been exchanged with a halide perovskite precursor, acquiring a smooth and compact quantum dot film. The photoconductive detector based on HgSe/CsPbBrxI3-x heterojunction presents a distinct photoelectric response under an incident light of 630 nm. The work provides a promising strategy to construct CQD-based heterojunctions, simultaneously achieving inorganic ligand exchange, which paves the way to obtain high-performance photodetectors based on CQD heterojunction films.

Colloidal quantum dots and two‐dimensional material heterostructures for photodetector applications

AbstractPhotodetectors (PDs) are optoelectronic devices that convert optical signals into electrical responses. Recently, there has been a tremendous increase in research interest in PDs based on colloidal quantum dots (QDs) and two‐dimensional (2D) material heterostructures owing to the strong light‐absorption capacity and the well‐adjustable band gap of QDs and the superior charge carriers transfer ability of 2D materials. In particular, the heterojunction formed between QDs and 2D materials can effectively enhance the separation and transport of photogenerated charge carriers, which is expected to establish PDs with ultrahigh photoconductive gain, high responsivity, and detectivity. This review aimed to summarize the state‐of‐the‐art advances in the research of QDs/2D material nanohybrid PDs, including the device parameters, architectures, working mechanisms, and fabrication technologies. The progress of hybrid PDs based on the heterojunction of QDs with different 2D materials, along with their innovative applications, are comprehensively described. In the end, the challenges and feasible strategies in future research and development are briefly proposed.

Cation-Exchanged quantum Dot-Based high-performance near-infrared photodetectors through surface treatment and passivation

Cation-exchange (CE) is a straightforward method for synthesizing colloidal quantum dots (CQDs) comprising multiple elements. However, the responsivity of photoconductors using cation-exchanged CQDs remains limited due to surface traps induced by the CE process. In this study a flexible near-infrared (NIR) photoconductive detector that exhibits the high responsivity (457 mA/W) under NIR light compared to reported Ag2Se CQD photodetector is fabricated using partially cation exchanged CdxAg2-xSe CQDs. The as-synthesized CdSe CQDs were transformed into CdxAg2-xSe CQDs through the introduction of an Ag precursor to enhance their NIR absorption characteristics and preserve their cubic structures. To mitigate surface traps associated with cation-exchanged CQDs, solution-phase ligand-exchange and post-treatment for surface passivation are incorporated using InBr3. In and Br ions are utilized to fill the surface vacancies of the CQDs and passivate the dangling bonds, reducing nonradiative recombination sites. Structural and optical analyses confirm the passivation of trap states. In addition, indium passivation improves the Seebeck coefficient and mobility, resulting in enhanced responsivity. This study underscores the importance of surface passivation in the CE method, thereby contributing to the future CQDs development with multiple elements.

First-principles investigation of structural electronic magnetic and thermodynamic properties of CdS alloyed with Co transition metal

This research work investigates the structural, electronic, and magnetic properties of Cd1–xCoxS compounds. The supercells with 16 atoms have been studied by substituting a Cd atom with a Co atom in the cubic unit cell CdS from x = 0 to x = 1 in a Zinc-Blende structure based on the first principles of spin-polarized density functional theory as implemented in the WIEN2k code. The full potential augmented plane wave method FP-LAPW (Full potential linear augmented plane wave) was used in this study to evaluate the structural properties of the compounds, the exchange–correlation term is based on the PBE-GGA (Perdew–Burke–Ernzerhof generalized gradient approximation). For other properties, such as electronic structures, densities of states, and magnetic properties, the TB-mbj GGA (Tight Binding modified Becke–Johnson) exchange potential approximation is utilized. In addition to these properties, the thermodynamic properties were added advantage to clarify their comportment as temperature variation. The analysis of the density of spin-polarized states showed the ferromagnetic character with a from x = 0.125 to x = 0.875. The calculated total magnetic moments of Cd1–xCoxS are addressed concerning the change in lattice parameters. To track the shift brought on by adding Co, we ran our calculationsfrom x = 0.125 to x = 0.875 for Cd1–xCoxS compounds. Hence, the negative energyformation indicates that our compound can be made experimentally. The material may be used for solar cell applications. In summary, our findings represent a guide for future research. The findings of this work might provide useful direction for the usage of this alloy system in a variety of device applications, For example in high-efficiency tandem solar cells, magnetic sensors, and photoconductive detector applications.

Identifying and Understanding the Positive Impact of Defects for Optoelectronic Devices

AbstractDefects are generally regarded to have negative impacts on carrier recombination, charge transport, and ion migration in materials, which thus lower the efficiency, speed, and stability of optoelectronic devices. Meanwhile, lots of efforts which focused on minimizing defects have greatly improved the performances of devices. Then, can defects be positive in optoelectronic devices? Herein, relying on in‐depth understanding of defect‐associated effects in semiconductors, trapping of photo‐generated carriers by defects is applied to enlarge photoconductive gain in photodetection. Therefore, the record photoconductive gain, gain‐bandwidth product, and detection limit are achieved in this photodetector. Exceeding the general concept that defects are harmful, a new view that the defects can be positive in photodetection is identified, which may guide to design high‐performance photodetectors.

Doping a metal–organic framework material (ZIF-8) on a perovskite photoconductive detector for improving stability and photoresponsivity

We proposed a new method to achieve efficient mixing of MAPbI3 and ZIF-8 nanoparticles that does not require heating treatment, solvent treatment, or a vacuum process. On this basis, a 10 × 10 array of planar photoconductive detectors was prepared.

Influence of Coupled Structural Parameters of Photoconductive Antennas on the Terahertz Narrowband Detection Performance of High Sensitivity and Frequency Selection

Narrowband terahertz (THz) detection plays a key role in biomedical imaging, biological applications, and security screening. Particularly rapid resolution of material differences based on spectral fingerprints or time‐resolved observation of the materials conformational state typically requires only the measurement of spectral information at a few selected frequencies. Here, a high‐performance resonance‐based coupled photoconductive antenna (PCA) was designed, which consists of a square split‐ring resonator (SRR) and an H‐shaped antenna. The incident THz wave energy can be effectively coupled in the gap of the H‐shaped antenna, and the coupling effect base on coupled harmonic oscillator model can be effectively strengthened. By decreasing the square SRR gap width HD, the relative position parameters of d and L3 between the square SRR and H‐shaped antenna can markedly improve the resonance frequency sensitivity with inductive–capacitive resonance. With the square SRR arm length L1 = L2 = L increased, the resonance frequency markedly shifted toward a lower frequency and the resonance sensitivity increased. The results prove that the THz frequency selection detection range of the coupled PCA can be designed to 0.1∼1.0 THz. Compared with the traditional H‐shaped photoconductive detection antenna, the detection resonance peak shifted the lower frequency and the maximum THz detection sensitivity increased by approximately two orders of magnitude at 0.2528 THz. The structure of the noncontact micrometer–coupled PCA is simple and easy to fabricate and integrate. Our findings may also help to advance the use of THz technology in rapid distinguish material properties.

Ultralow Dark Current (6 fA at 1 V) in Quasi-Two-Dimensional CsGaGeSe4 Single Crystals for High Signal-to-Noise Ratio Photodetectors under Strong Electron Localization.

To satisfy the demands of photodetectors for weak-light detection, materials selected for device fabrication should have an extremely low background carrier concentration to suppress the dark current of devices. In this work, a new quasi-two-dimensional CsGaGeSe4 single crystal with an extremely low background carrier concentration was synthesized by a co-solvent reaction based on which a photoconductive detector was prepared with an ultralow dark current density (6 fA at 1 V and ∼10-10 A cm-2) and a high response speed (∼0.74 s) was achieved, presenting a great potential of being applied to the field of weak-light detection. The ultralow dark current density originates from both the good crystal quality and the strongly asymmetric band structure of CsGaGeSe4. In the darkness, electrons locally bound in the valence band bring an ultralow dark current density; after illumination, the electrons transiting to the conduction band will participate in the conduction in a non-localized state, resulting in a high signal-to-noise ratio. This work not only provides a new choice of potential materials for weak-light detection but also proposes an effective strategy for material selection.

High performance CsPbBr3 epitaxial film photodetector with ultralow dark current and record detectivity

At present, spin coating is commonly used for perovskite film detectors, which has large photocurrent in the dark state due to the poor control on film growth and low crystal quality. In this Letter, pulsed laser deposition has been introduced to grow high quality CsPbBr3 epitaxial films, and the effect of substrate temperature on the film quality was studied during the epitaxial process. Planar metal–semiconductor–metal photoconductive detectors based on such epitaxial CsPbBr3 thin films with dark current as low as 11 pA at a bias voltage of 2 V was achieved. Under the illumination of a 450 nm laser with a power density of 0.65 μW cm−2, the responsivity, external quantum efficiency, and detectivity of the devices reach 12.796 AW−1, 2996%, and 3.38 × 1014 Jones, respectively. The maximum on/off ratio can be 2.38 × 105 under high-intensity 450 nm laser irradiation of 148 mW cm−2. In contrast, the spin-coated CsPbBr3 film-based detector with the same device configuration exhibit dark current that is two orders of magnitude higher and an on/off ratio of three orders of magnitude smaller than those of the epitaxial film devices. Therefore, due to their high-quality, thickness-control, and easy-integration, such epitaxial perovskite thin films can be used as a platform for the study of more functionalities of halide perovskite semiconductors and related devices.

Design and deposition of ZnS antireflection coating for high-performance mid-infrared PbSe photoconductive detectors fabricated by chemical bath deposition

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.

Ultrasensitive Room Temperature Infrared Photodetection Using a Narrow Bandgap Conjugated Polymer.

Photodetectors operating across the short-, mid-, and long-wave infrared (SWIR-LWIR, λ = 1-14µm) underpin modern science, technology, and society in profound ways. Narrow bandgap semiconductors that form the basis for these devices require complex manufacturing, high costs, cooling, and lack compatibility with silicon electronics, attributes that remain prohibitive for their widespread usage and the development of emerging technologies. Here, a photoconductive detector, fabricated using a solution-processed narrow bandgap conjugated polymer is demonstrated that enables charge carrier generation in the infrared and ultrasensitive SWIR-LWIR photodetection at room temperature. Devices demonstrate an ultralow electronic noise that enables outstanding performance from a simple, monolithic device enabling a high detectivity (D*, the figure of merit for detector sensitivity) >2.44 × 109 Jones (cm Hz1/2 W-1 ) using the ultralow flux of a blackbody that mirrors the background emission of objects. These attributes, ease of fabrication, low dark current characteristics, and highly sensitive operation overcome major limitations inherent within modern narrow-bandgap semiconductors, demonstrate practical utility, and suggest that uncooled detectivities superior to many inorganic devices can be achieved at high operating temperatures.

Preparation and Performance Study of Photoconductive Detector Based on Bi2O2Se Film

Bi2O2Se, as a novel two-dimensional semiconductor material, has been prepared and used in the field of photodetection. Herein, Bi2O2Se nanosheets were prepared using a hydrothermal method. Bi2O2Se films were also prepared using a drop-coating method. A photoconductive detector based on the Bi2O2Se film was constructed. The influence of nanosheet size was considered. Ultrasonic crashing treatments and different drying processes were used for the improvement of device performance. The obtained results demonstrate that the Bi2O2Se film based on treated nanosheets is denser and more continuous, leading to a higher photocurrent (1.4 nA). Drying in a vacuum can further increase the photocurrent of the device (3.0 nA). The photocurrent would increase with the increase in drying temperatures, while the dark current increases synchronously, leading to a decrease in the on/off ratio. The device based on Bi2O2Se film was dried in a vacuum at 180 °C and exhibited high responsivity (28 mA/W) and detectivity (~4 × 109 Jones) under 780 nm light illumination. Together, these results provide a data foundation and vision for the further development of photodetectors based on Bi2O2Se material.

Calibration of terahertz sampling detectors for intense unipolar picosecond current pulses in waveguides

Terahertz pulses are nowadays commonly used in many areas of condensed matter physics to access material properties and explore transport phenomena at fast timescales. However, little work has been devoted to the full characterization of such pulses when confined in waveguides. In this work, we fabricate terahertz photoconductive switch detectors, located at various points along a coplanar waveguide, and sample the electrical pulses that pass by the detectors. Two different but consistent methods were developed to calibrate the pulse amplitude. Notably, we synchronize a commercial pulse generator with the laser in order to sample nanosecond-wide pulses with the photoswitch detectors, effectively turning the setup into an on-chip high-frequency sampling oscilloscope. Both methods give identical results on pulse current, voltage, and field amplitudes and enable an absolute characterization of the electrical pulse propagation along the waveguide. These techniques constitute a reliable tool to explore (non-linear) phenomena such as current or field induced magnetization switching or phase transitions, which take place at high THz intensities.