Vertical Photodetectors Research Articles

Layer Number Controllable Molybdenum Disulfide Film Growth and Its Applications in Vertical and Planar Photodetectors

Layer Number Controllable Molybdenum Disulfide Film Growth and Its Applications in Vertical and Planar Photodetectors

4H-SiC ultraviolet photodetector array with vertical MSM configuration

Abstract The increasing demand for ultraviolet (UV) imaging in extreme conditions, such as high temperatures and strong radiation, has spurred advancements in UV photodetector arrays. Traditional metal-semiconductor- metal (MSM) 4H-SiC UV photodetector array, with their planar structure and M×N electrode connections, face challenges in circuit design. Our research utilizes a vertical design for building the photodetector array, reducing the connections to just M+N, thereby simplifying the circuit design and signal processing. Utilizing semi-insulating 4H-SiC wafer and TiN electrodes, we developed an 8×8 vertical MSM photodetector array. Tested under a 365 nm light source at 10.5 mW/cm2 and a 5V bias, the array demonstrated low dark currents, high contrasts under illumination, and a 100% operational yield. With average photo current and dark currents of 1.56×10-8 A and 2.94×10-13 A, respectively, the average photo-to-dark current ratio (PDCR) exceeded 5×104 Our design effectively minimized sneak path currents and achieved a low crosstalk rate of 0.46%, enabling the capture of clear, high-contrast images. This marks a significant advancement in the application of MSM 4H-SiC UV photodetectors for imaging in extreme conditions.

Ultra‐Fast Weak Light Detectors Based on van der Waals Stacked 2D Semiconductor/h‐BN Heterostructures

AbstractFast and sensitive detectors for weak light are crucial in various fields like real‐time monitoring, medical diagnosis, and astronomy. However, photodetectors using 2D materials face challenges in achieving both a low detection limit for weak light and fast response. Here, a vertical vdW graphene/indium selenide (InSe)/hexagonal boron nitride (h‐BN) heterostructure on a gold electrode is provided, demonstrating an ultra‐low detection limit of 47.4 nW cm−2 and an ultra‐fast response speed of 327 ns. Vertical photodetectors feature nanoscale channel length, thus reducing scattering and recombination of carriers. The high potential barrier of multilayer h‐BN effectively blocks carrier transport, resulting in ultra‐low dark current and minimal power dissipation. Additionally, enhanced light absorption in InSe by the metal‐insulator‐semiconductor structure improves the sensitivity to weak light detection. More importantly, the built‐in field at the graphene/InSe interface can promote the separation of photo‐generated carriers to improve the collection efficiency. These factors jointly reduce the detection limit and response time simultaneously for weak light. This vertical vdW heterostructure comprising a 2D semiconductor/h‐BN offers a solution to make the majority of 2D semiconductors applicable in ultra‐fast weak light detectors.

Robust Growth of 2D Transition Metal Dichalcogenide Vertical Heterostructures via Ammonium-Assisted CVD Strategy.

Two dimension (2D) transition metal dichalcogenides (TMD) heterostructures have opened unparalleled prospects for next-generation electronic and optoelectronic applications due to their atomic-scale thickness and distinct physical properties. The chemical vapor deposition (CVD) method is the most feasible approach to prepare 2D TMD heterostructures. However, the synthesis of 2D vertical heterostructures faces competition between in-plane and out-of-plane growth, which makes it difficult to precisely control the growth of vertical heterostructures. Here, a universal and controllable strategy is reported to grow various 2D TMD vertical heterostructures through an ammonium-assisted CVD process. The ammonium-assisted strategy shows excellent controllability and operational simplicity to prevent interlayer diffusion/alloying and thermal decomposition of the existed TMD templates. Ab initio simulations demonstrate that the reaction between NH4Cl and MoS2 leads to the formation of MoS3 clusters, promoting the nucleation and growth of 2D MoS2 on existed 2D WS2 layer, thereby leading to the growth of vertical heterostructure. The resulting 2D WSe2/WS2 vertical heterostructure photodetectors demonstrate an outstanding optoelectronic performance, which are comparable to the performances of photodetectors fabricated from mechanically exfoliated and stacked vertical heterostructures. The ammonium-assisted strategy for robust growth of high-quality vertical van der Waals heterostructures will facilitate fundamental physics investigations and device applications in electronics and optoelectronics.

Vertical van der Waals Integrated p‐W0.09Re0.91S2 /GaN Heterojunction for Ultra‐High Detectivity UV Image Sensing

AbstractThe relentless advancement of van der Waals (vdW) heteroepitaxy technology has charted an expansive horizon for the integration and functionalization of heterogeneous materials. In this research, a 2D/3D vdW heterojunction photodetector based on p‐W0.09Re0.91S2/n‐GaN integrated on a Free‐standing (FS)‐GaN substrate, encompassing horizontal, quasi‐vertical, and vertical structures is have successfully fabricated. By incorporating a suite of performance enhancement strategies, including mixed‐dimensional stacking, p‐type doping, type‐II band alignment, and vertical structure design, the developed vertical structure photodetector has exhibited exceptional performance. Specifically, the detector achieves a high Responsivity of up to 497.60 A W−1, an impressive specific Detectivity of 8.41 × 1013 Jones, and a fast response speed (rise/decay time of 10 ms/20 ms). Additionally, the device is successfully applied in the realm of single‐pixel imaging, substantiating its potential for practical applications. The findings of this work not only signify notable strides in integration and optoelectronic performance within the optoelectronic device domain but also portend novel breakthroughs in imaging technology applications, bestowing renewed vigor and endless potential upon the evolution of this field.

Vertical heterojunction photodetector of In2Se3/PtS2 with high polarization sensitivity and tunable electronic characteristics

A monolayer In2Se3 root number model was used with a monolayer PtS2 material 2 × 2 × 1 cell expansion to form an In2Se3/PtS2 bilayer with a lattice mismatch of 3.12 %. Utilizing first principles calculations, we systematically explore the structural, electrical, and optical characteristics of In2Se3/PtS2 heterostructures. The stabilized heterostructure displays an indirect band gap of 1.62 eV and a type I energy band arrangement. Moreover, the absorption spectra further demonstrate the heterostructure's ability to capture visible and UV light, it is significantly better than monolayer In2Se3 and monolayer PtS2, and the absorption peak at a wavelength of 185 nm is as high as 8. 07×105/cm. Using biaxial strain to change the heterojunction energy band structure, it is found that as the biaxial strain field changes, the hetero-structure of In2Se3/PtS2 transforms from a type I to a type II energy band arrangement with the applied stresses of −8 %, 2 %, 4 %, 6 %, and 8 %. Transitioning from simulations to practical applications, we model a novel photodetector based on the In2Se3/PtS2 heterojunction. Remarkably, the In2Se3/PtS2 heterojunction photodetector demonstrates high polarization sensitivity at a photon energy of 3.2 eV, boasting a maximum extinction ratio of 20, outperforming alternatives. In summary, the In2Se3/PtS2 heterostructure presents exceptional optical properties, providing a robust foundation for advanced photodetector applications.

Self-Powered ZnO@PdTe2/Si Heterojunction Photodetector with an Ultrafast Response for Color Imaging and Optical Communication.

Broadband photodetectors have attracted much attention due to their multispectral response properties and show great potential in the fields of optical sensing, multispectral imaging, and optical communications. Palladium telluride (PdTe2) is highly competitive in broadband detection due to its tunable bandgap and nonlinear optical properties. However, the low response speed hinders further improvement in the performance of PdTe2-based broadband photodetectors. In this work, we present island-type ZnO@PdTe2 composites on Si as a heterojunction photodetector exhibiting highly sensitive photodetection capabilities in a wide band from the solar-blind region (254 nm) to the short-infrared (1.55 μm). Due to the island-type morphology of the ZnO@PdTe2 composites effectively enhancing light absorption and the ZnO@PdTe2/Si stacks forming a type-II heterojunction accelerating carrier separation, the devices have an ultrafast response (1.58/1.34 μs), a detectivity of up to 1.56 × 1013 Jones, and a sensitivity of up to 107 cm2/W. A triple-channel color imaging system and a dual-channel data transmission system were developed based on the excellent and stable performance of the device. This study demonstrates the great potential of ZnO@PdTe2/Si vertical heterojunction photodetectors for high-speed, wide-band, multiscenario optical communication.

Multilayer Graphene/Epitaxial Silicon Near‐Infrared Self‐Quenched Avalanche Photodetectors

Abstract2D materials and their heterostructures exhibit considerable potential in the development of avalanche photodetectors (APDs) with high gain, response, and signal‐to‐noise ratio. These materials hold promise in addressing inherent technical challenges associated with APDs, such as low light absorption coefficient, elevated noise current, and substantial power consumption due to high bias resulting in only moderate current gain. In this work, a macro‐assembled graphene nanofilm (nMAG)/epitaxial silicon (epi‐Si) vertical heterostructure photodetector with a responsivity of 0.38 A W−1 and a response time of 1.4 µs is reported. The photodetectors use high‐quality nMAG as the absorption layer and a lightly‐doped epi‐Si layer as the multiplication region under the avalanche mode to provide a high responsivity (2.51 mA W−1) and detectivity (2.67 × 109 Jones) at 1550 nm, which can achieve high‐resolution imaging. In addition, the APD displays a weak noise level and an avalanche gain of M = 1123. It can work with relatively low avalanche turn‐on voltages and achieve self‐quenching by switching from illumination to dark during avalanche multiplication, with a real‐time data transfer rate of 38 Mbps in near‐infrared light communication data links. The proposed structure enables the fabrication of high‐performance APDs in the infrared range using complementary‐metal‐oxide‐semiconductor (CMOS)‐compatible processes.

Enhanced photovoltaic response in WSe2 photodetector with asymmetric two-dimensional contacts

Asymmetric contact pairs with different work functions provide an efficient method to extract photogenerated carriers in optoelectrical devices. Specifically, vertical optoelectrical devices based on two-dimensional (2D) materials utilize graphene layers as the bottom and top contacts. Whereas an additional terminal is required for electrostatic doping in either top or bottom graphene to enlarge the built-in electric field. Herein, we present an enhanced photovoltaic response in a vertical WSe2 photodetector utilizing asymmetric 2D contacts. A graphite layer and a degenerate SnSe2 are used as the top and bottom contacts, respectively, with a significant difference in their work functions. By establishing a large built-in electric field across the vertical WSe2 layer, a strong photovoltaic effect is achieved, resulting in an open-circuit voltage of 0.37 V and a short-circuit current of 0.42 μA under 532 nm illumination. The device shows high-performance photodetection characteristics, with a responsivity of 32.04 A W−1, external quantum efficiency of 7475%, and specific detectivity of 3.61 × 1012 Jones. Furthermore, the device can generate a maximum output electrical power of 70.9 nW, enabling a high-power conversion efficiency of 3.5%.

Interface‐Engineering Induced Swift and Controllable Solar‐Blind Photoresponse in Ga2O3/SiC Heterojunction Based on Unconventional Rectification Characteristics

AbstractGa2O3 photodetectors with demonstrated high sensitivity provide a potential subversive scheme for solar‐blind photodetection. However, the planar structure and the relatively slow response speed of the device have restricted the integration and application of Ga2O3 photodetectors. Herein, a narrow SiO2 barrier layer is introduced on the commercial SiC substrate, and a vertical photodetector is realized based on β‐Ga2O3/SiO2/SiC heterostructure with controllable tunneling effect by tailoring the band structure at the interface. The developed device exhibits unconventional rectification characteristics and photoresponse performance in different biasing modes owing to the controllable tunneling effect at the interface. In particular, the photodetector achieves a high responsivity (186.8 A W−1) under solar‐blind illumination at reverse bias, while exhibiting obvious advantages in dark current (3 pA), photo‐to‐dark current ratio (8.8 × 106), linear dynamic range (138.8 dB), and specific detectivity (1.4 × 1015 Jones) at forward bias. The photodetector also demonstrates excellent photoresponse stability after 6 months in air without encapsulation. In addition, an alternating biasing strategy, inspired by its bidirectional operability, is proposed to suppress the persistent photoconductivity effect and increase the decay speed by 1.23 × 105 times. This work provides a referable strategy for the further development of high‐performance Ga2O3‐based photoelectronics.

Highly stable and sensitive broadband photodetector based on BA2MAPb2I7/Si heterojunction

Quasi-2D perovskites have gained significant attention as promising two-dimensional materials for optoelectronic applications. They offer unique optical and electrical properties as well as enhanced stability compared to their 3D counterparts. In this study, we present the successful fabrication of a novel photodetector based on a BA2MAPb2I7/Si heterojunction. The optoelectronic properties of the BA2MAPb2I7/Si-based photodetector demonstrate its high sensitivity across a broad range of incident wavelengths spanning from 365 nm to 850 nm. Notably, the fabricated device exhibits an exceptional responsivity of 3.53 A/W for 850 nm radiation, surpassing the typical few mA/W responsivities achieved by a majority of previously reported perovskite-based vertical photodetectors. Furthermore, the device shows a rapid response of approximately 25.9 μs. These results highlight the potential of our fabrication approach to realize highly sensitive broadband photodetectors using a simple and cost-effective process, making them suitable for integration with Si-based electronics.

Design and optimization of the performance of PbS quantum dot based vertical photodetector

Abstract Quantum dots (QDS) are widely used as photoactive materials for various optoelectronic applications, such as light-emitting diodes, photodetectors, lasers, and solar cells, because of their unique and outstanding physical properties for fabricating devices via solution-processing techniques and for varying the sizes of QD to modulate the band gap. In this study, we constructed a numerical model of a vertical photodetector using lead sulfide (PbS) quantum dot layer undergoing ligand exchange treatment with tetrabutylammonium iodide (TBAI) as the light absorption layer to obtain an optimized high-performance photodetector using 1D-Solar Cell Capacitance Simulator (SCAPS) software. For the hole transport layer (HTL) and electron transport layer (ETL), a PbS quantum dot layer that employs an ethanedithiol (EDT) ligand exchange scheme and a zinc oxide (ZnO) layer were utilized, respectively, with gold (Au) and indium tin oxide (ITO) as the bottom and upper electrodes, respectively. After optimizing the thickness and doping concentration of the absorption layer, we obtained a maximum responsivity of 0.4675 A W−1 and detectivity of 2.44 * 10 13 Jones at a reverse bias of 0.5 volts after optimizing of thickness and doping concentration of absorption layer showing an improvement of 19% and 87.7% respectively compared to the initial structure whose parameters originated from studies of PbS quantum dot solar cells with the same structure and materials, although optimization of other transport layers do not provide as great performance enhancement as absorption layer. This study demonstrates that the structural parameters of solar cells are not always applicable to photodetectors, and that photodetectors have great potential for numerical optimization. Ethical Compliance: All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Giant Negative Photoresponse in van der Waals Graphene/AgBiP2Se6/Graphene Trilayer Heterostructures.

The positive photoconductive (PPC) effect is a well-established primary detection mechanism employed by photodetectors. In contrast, the negative photoconductive (NPC) effect is not extensively investigated thus far, and research on the NPC effect is still in its early stage. Herein, a quaternary van der Waals material, AgBiP2Se6 atomic layers, is discovered to achieve a giant NPC effect. Through experimental observations in a Graphene/AgBiP2Se6/ Graphene-based vertical photodetector, an irreversible conversion is identified from common PPC photoresponse to atypical NPC photoresponse. Notably, this device demonstrates an exceptionally high negative responsivity (R) of 4.9×105AW-1, surpassing the previous records for NPC photodetectors. Additionally, it exhibits remarkable optoelectronic performances, including an external quantum efficiency of 1.3×108% and a detectivity (D) of 3.60×1012Jones. The exceptionally high NPC photoresponse observed in this device can be attributed to the swift suppression of photogenerated free carriers at robust recombination centers situated at significant depths, induced by the elevated drain-source voltage bias. The remarkably high NPC photoresponse also positions AgBiP2Se6 as a promising 2D material for multifunctional optoelectronic devices and an excellent platform for systematic exploration of the NPC effect.

Chemically and physically enhanced adhesion for robust interfaces in all-soft vertical organic photodetectors.

We report all-soft vertical organic photodetectors composed of only soft components. Chemically and physically enhanced interfacial adhesion between layers enables robust operation under mechanical deformation. Their excellent light-sensing capability and deformable features, combined with powerless operation, promise significant advancements in optoelectronic applications.

Broadband photodetectors from silane-passivated CsPbBr3 nanocrystals by ultrasound-mediated synthesis.

Perovskite nanocrystals have excellent optical properties but suffer from environmental instability and production up-scaling which limit their commercial application. Here, we report the gram-scale ultrasound-mediated synthesis of silane passivated CsPbBr3 nanocrystals using (3-aminopropyl) triethoxysilane (APTS) as the primary surface ligand surface. The surface engineering endowed the CsPbBr3@SiOR NCs with extended environmental stability, a narrow emission bandwidth and a high photoluminescence quantum yield (PLQY > 75%). Thanks to these excellent optical properties, high-efficiency lateral and vertical photodetectors were fabricated. In particular, the layered vertical photodiode composed of ITO/Ga2O3/CsPbBr3/Au exhibited a broadband photoresponse from 350-700 nm with a responsivity peaking at 44.5.1 A W-1 and specific detectivity above 1013 Jones when illuminated at 470 nm wavelength and biased at +5 V. These results correspond to the best-in-class performance perovskite nanocrystal PD and confirm the extraordinary potential of CsPbBr3@SiOR for the development of efficient optoelectronic devices.

Concurrent Thermal Reduction and Boron-Doped Graphene Oxide by Metal–Organic Chemical Vapor Deposition for Ultraviolet Sensing Application

We synthesized a boron-doped reduced graphene oxide (BrGO) material characterized by various electrical properties, through simultaneous thermal reduction and doping procedures, using a metal–organic chemical vapor deposition technique. X-ray photoelectron spectroscopy (XPS) was used to study the impact of the doping level on the B bonding in the reduced graphene oxide (rGO) layer that is influenced by the annealing temperature. The synthesized BrGO layer demonstrated a high B concentration with a considerable number of O-B bonds, that were altered by annealing temperatures. This resulted in a decreased work function and the formation of a Schottky contact between the BrGO and n-type Si substrate. Due to the higher proportion of B-C and B-C3 bonding in the BrGO/Si device than that in the rGO/Si, the decreased Schottky barrier height of the BrGO/n-Si vertical junction photodetector resulted in a higher responsivity. This study showcases a promise of a simple B-doping method in use to alter the electrical characteristics of graphene materials.

A solar-blind vacuum-ultraviolet photodetector based on free-standing lamellar aluminum nitride single crystal

High-quality aluminum nitride (AlN) crystals are the key material for the development of high-performance solid-state solar-blind vacuum-ultraviolet (VUV) photodetectors. However, the commonly used epitaxial method to grow AlN crystals would limit this development due to the existence of indispensable substrates. This study addresses this issue using free-standing lamellar AlN single crystals that are grown using the physical vapor transport method. The large lateral dimension of the crystal enables the construction of an Au-AlN-graphene van der Waals heterojunction, which can function as a vertical VUV photodetector with the graphene serving as the light window. The asymmetric junctions formed on the two sides of the crystal and the limited penetration of the VUV endow the device with a bias polarity-dependent photoresponse feature arising from different photoelectric processes. Furthermore, the device demonstrates a high responsivity of 5.77 A W−1 and a high specific detectivity of 1.71 × 1013 cm Hz1/2 W−1 under the illumination of a 193 nm laser. The high crystallinity of the AlN guarantees a high spectral selectivity of responsivity with a 193 nm/280 nm rejection ratio of 3 × 102. This work would inspire the development of wide-bandgap-semiconductor-based VUV photodetectors in terms of methodology and mechanism.

High-Performance Photodetectors Based on Semiconducting Graphene Nanoribbons.

The inherent zero-band gap nature of graphene and its fast photocarrier recombination rate result in poor optical gain and responsivity when graphene is used as the light absorption medium in photodetectors. Here, semiconducting graphene nanoribbons with a direct bandgap of 1.8 eV are synthesized and employed to construct a vertical heterojunction photodetector. At a bias voltage of -5 V, the photodetector exhibits a responsivity of 1052 A/W, outperforming previous graphene-based heterojunction photodetectors by several orders of magnitude. The achieved detectivity of 3.13 × 1013 Jones and response time of 310 μs are also among the best values for graphene-based heterojunction photodetectors reported until date. Furthermore, even under zero bias, the photodetector demonstrates a high responsivity and detectivity of 1.04 A/W and 2.45 × 1012 Jones, respectively. The work shows a great potential of graphene nanoribbon-based photodetection technology.

Vertical heterojunction photodetector with self-powered broadband response and high performance

The development trend of modern electronics and optoelectronics is constantly moving towards highly integrated, comprehensive, and miniaturized devices. Vertical configuration provides an easy means to achieve higher integration density than traditional planar configuration, and possess higher carrier generation capabilities and transfer speed, which can further enhance the performance of optoelectronic devices. This technology holds tremendous potential for designing the next generation of electronic/optoelectronic devices. In this work, we developed a vertical heterojunction photodetector, which combines narrow-bandgap 2D topological insulator Bi2Se3, ultra-wide-bandgap amorphous Ga2O3, and high-performance p-Si substrate, achieving broad-spectrum detection from 254 to 1000 nm and significantly shortened response time due to the advantage of carrier vertical transmission. The response time of the device is less than 50 ms under illumination with different wavelengths. Moreover, the device exhibits self-powered characteristics, with maximum responsivity and detectivity of 0.175 mA/W and 1.58 × 1010 Jones, respectively, under 365 nm light irradiation at zero bias. A switch ratio as high as 103 is demonstrated under 365 and 470 nm illumination, highlighting the high performance of device. Additionally, the device displays excellent stability and imaging capability. Our research provides a promising and instructive prospect for the practical application of vertical broadband self-powered heterojunction PDs in a wider range of fields.

Design and numerical analysis of CsSn0.5Ge0.5I3 vertical photodetector using SCAPS-1D

Design and numerical analysis of CsSn0.5Ge0.5I3 vertical photodetector using SCAPS-1D