Ultrasensitive Photodetectors Research Articles

Ultrasensitive Photodetectors Promoted by Interfacial Charge Transfer from Layered Perovskites to Chemical Vapor Deposition‐Grown MoS2

Heterostructures for charge-carrier manipulation have laid the foundation of modern optoelectronic devices, such as photovoltaics and photodetectors. High-performance heterostructure devices usually impose stringent requirements on the material quality to sustain efficient carrier transport and charge transfer, thus leading to sophisticated fabrication processes. Here, a simple yet efficient strategy is proposed to develop ultrasensitive photodetectors based on heterostructures of chemical vapor deposition-grown MoS2 and polycrystalline-layered perovskites. The layered perovskites possess pure crystallographic orientation with conductive edges in contact with MoS2 , which gives rise to efficient light absorption, exciton diffusion, and interfacial charge transfer. In dark state, the mismatch of work functions of two materials facilitates low dark currents by the depletion of electrons in MoS2 . Under light irradiation, efficient exciton diffusion and interfacial charge transfer are realized in the heterostructures with type-II band alignment, which produces drifting electrons in MoS2 and leaves trapped holes in layered perovskites. The photodetectors present suppress noises and boost photocurrents, yielding a champion device with a responsivity of 2.5×104 AW-1 , and a specific detectivity of 4.1×1014 Jones. The results demonstrate a scalable approach for the integration of high-performance devices with high tolerance to defects.

Ultrasensitive self-powered UV photodetector based on a novel p-n heterojunction of solution-processable organic semiconductors

This work reports a highly sensitive self-powered ultraviolet photodetector, which is based on the active layer of NPD:Alq3 with different Alq3 contents. All solution-processed technique was utilized to fabricate the active layers of the devices to achieve an optimized system that exhibits highly sensitive and stable photodetector under self-powered operation mode. The values of photosensitivity, responsivity, and detectivity of the photodiodes at zero-bias were estimated at 1.30 × 105, 1.07 mA/W, 1.04 × 1011 Jones, respectively. The rise and decay times of the optimized device were estimated at 0.34 s and 0.28 s, respectively. For practical application of the device sensing efficiency, the optimal load line of self-powered UV photodetector to deliver the maximum power was estimated of an internal impedence of 0.579 MΩ. In conclusion, the high sensitivity, good stability, and fast response/recovery speed of the self-powered UV photodetector make the devices applicable to resolve some of the current issues in UV detection.

Spectroscopic ellipsometry of amorphous Se superlattices

Superlattice structures have a variety of electrical and optical properties that allow for interesting applications like quantum cascade lasers and ultrasensitive photo-detectors. However, such structures require high-tech fabrication methods like molecular beam epitaxy, and this technology barrier means that these promising devices are not in widespread use. Using the simple method of rotational evaporation, we fabricated films with alternating multi-nanolayers of amorphous selenium (Se) and arsenic selenide (As2Se3). We investigated the optical properties of the individual materials, and the resulting multi-layer structure using spectroscopic ellipsometry. The results were modeled using Cody–Lorentz oscillators to obtain the refractive index (n) and extinction coefficient (k). The models showed the optical band gaps of Se and As2Se3 to be 1.97 and 1.69 eV, respectively. The absorption coefficient (α) of the multi-layer structure showed a series of five ‘steps’ in energy at 1.72, 1.82, 1.89, 1.97, and 2.04 eV. These are confirmed to stem from the transitions between confined quantum well levels due to the superlattice structure. In this way, the optical measurement using spectroscopic ellipsometry confirms the possibility of fabricating good quality nanostructutres using amorphous materials and rotational evaporation.

Controlled growth of SnSe/MoS2 vertical p–n heterojunction for optoelectronic applications

Two-dimensional (2D) heterostructures have been widely studied in recent years and are envisioned to play a key role in future integrated electronics and optoelectronics. The thus-involved van der Waals integration technique provides a feasible way to integrate different 2D materials even with diverse crystal structures into heterostructures, providing a promising platform to explore new artificial materials with new properties. Here, for the first time, we have successfully realized the combination of orthogonal selenide (SnSe) with hexagonal MoS2 into p–n heterojunctions though a two-step chemical vapor deposition method. High resolution transmission electron microscopy characterization shows that multilayer SnSe nanosheet is vertically stacked on MoS2 nanosheet with high crystallinity. The precise spatial modulation of SnSe/MoS2 heterostructures is verified by Raman diagrams. At the same time, the electrical and optoelectronic properties are probed though designing SnSe/MoS2 p–n junction devices. Typical current rectification behaviors are obviously observed in dark condition. While under light illumination, obvious photovoltaic behavior is observed. Maximum short-circuit current (I sc) and photon-electron conversion efficiency (η) are measured to be 67 nA and 1.8%, respectively. The results also indicate that the heterostructure can be employed for reliable ultra-sensitive photodetection, where maximum photoresponsivity is measured to be 384 A W−1. The direct vapor growth of 2D p–n junctions with different lattice symmetries may expand the platform for the realization of new 2D electronic and optoelectronic devices.

Ultrahigh Deep-Ultraviolet Responsivity of a β-Ga2O3/MgO Heterostructure-Based Phototransistor

Deep-ultraviolet (DUV) photodetectors based on wide-band-gap semiconductors have attracted significant interest across a wide range of applications in the industrial, biological, environmental, and military fields due to their solar-blind nature. As one of the most promising wide-band-gap materials, β-Ga2O3 provides great application potential over detection wavelengths ranging from 230 to 280 nm owing to its superior optoelectronic performance, stability, and compatibility with conventional fabrication techniques. Although various innovative approaches and device configurations have been applied to achieve highly performing β-Ga2O3 DUV photodetectors, the highest demonstrated responsivity of the β-Ga2O3 photodetectors has only been around 105 A/W. Here, we demonstrate a β-Ga2O3 phototransistor with an ultrahigh responsivity of 2.4 × 107 A/W and a specific detectivity of 1.7 × 1015 Jones, achieved by engineering a photogating effect. A β-Ga2O3/MgO heterostructure with an Al2O3 encapsulation layer is employed not only to reduce photogenerated electron/hole recombination but also to suppress the photoconducting effects at the back-channel surface of the β-Ga2O3 phototransistor via a defect-assisted charge transfer mechanism. The measured photoresponsivity is almost 2 orders of magnitude higher than the highest previously reported value in a β-Ga2O3-based photodetector, to the best of our knowledge. We believe that the demonstrated β-Ga2O3/MgO heterostructure configuration, combined with its facile fabrication method, will pave the way for the development of ultrasensitive DUV photodetectors utilizing oxide-based wide-band-gap materials.

The catalyst-free growth of layer-structured CuInSe2/β-In2Se3 microwires for ultrasensitive self-powered photodetectors based on a lateral p–n junction

A new building-block of one-dimensional layer-structured CuInSe2/β-In2Se3 lateral p–n junction is realized for high-performance self-powered photodetector.

Ultrasensitive broadband photodetectors based on two-dimensional Bi2O2Te films

A broadband photodetector consisted by Bi2O2Te and n-Si exhibits an ultrasensitive performance in the range of 210 nm to 2400 nm.

All‐Dielectric Nanostructure Fabry–Pérot‐Enhanced Mie Resonances Coupled with Photogain Modulation toward Ultrasensitive In2S3 Photodetector

AbstractAs the fresh blood of 2D family, non‐layered 2D materials (2DNLMs) have demonstrated great potential in the application of next‐generation optoelectronic devices. However, stemming from the weak light absorption brought by atomically thin thickness and the interfacial recombination brought by surface dangling bonds, traditional 2DNLM photodetectors are always accompanied by limited performance. Herein, a structure that integrates Si nanopillar array and non‐layered 2D In2S3 to construct an ultrasensitive photodetector is designed. In particular, periodically Si nanopillars can act as Fabry–Pérot‐enhanced Mie resonators that can effectively control and enhance the light absorption of 2D In2S3. On the other hand, a vertical built‐in electric field is introduced in the In2S3 channel to capture photogenerated holes and leave electrons recycling in In2S3, obtaining a high photogain. Benefiting from these two mechanisms, this proposed photodetector presents a high responsivity of 4812 A W−1 and short rise/decay time of 5.2/4.0 ms at the wavelength of 405 nm. Especially, a high light on–off ratio greater than 106 and a record‐high detectivity of 5.4 × 1015 Jones are achieved, representing one of the most sensitive photodetectors based on 2D materials. This deliberate device design concept suggests an effective scheme to construct high‐performance 2DNLM optoelectronic devices.

2D MoS2/CuPc heterojunction based highly sensitive photodetectors through ultrafast charge transfer

Photodetectors (PD) with high detectivity, high quantum efficiency and fast response are fundamental units to achieve sensors, imagers, and many others functional optoelectronics. Here we demonstrate high performance vertical stacked 2D MoS2/CuPc heterojunction based photodetectors with high sensitivity, high external quantum efficiency and ultrafast response time. The functional p-type organic thin film of CuPc was thermally evaporated on n-type two-dimension (2D) MoS2 monolayer to create an ideal type II heterojunction interface, where ultrafast charge transfer (CT) occur in 16 ps, followed by effective exciton separation and charge collection. As a result, photoresponse time as fast as 436 μs has been obtained for 2D MoS2/CuPc PDs, as well as a profound responsivity of 3.0×103A/W and a detectivity of 2.0 × 1010 Jones with a peak external quantum efficiency (EQE) of 483%. This work suggests a feasible route to develop ultrasensitive visible light photodetector by 2D materials.

Ultrasensitive UV Photodetector Based on Interfacial Charge-Controlled Inorganic Perovskite-Polymer Hybrid Structure.

In this work, we demonstrate an ultrasensitive, visible-blind ultraviolet (UV) photodetector based on perovskite-polymer hybrid structure. A novel wide-band-gap vacancy-ordered lead-free inorganic perovskite Cs2SnCl6 with Nd3+ doping is employed in the active layer of this hybrid photodetector. Remarkably, with interfacial charge-controlled hole-injection operating mechanism, our device achieves a maximum detectivity of 6.3 × 1015 Jones at 372 nm, fast photoresponse speed with rise time and fall time in the order of milliseconds, and a large linear dynamic range of 118 dB. The performance is significantly better than most of the existing organic and inorganic semiconductor UV photodetectors reported so far, and its detectivity is close to 1 order of magnitude higher than that of the photomultiplication tube (PMT) in the UV region. In addition, the photodetector demonstrated excellent environmental stability, which is critical for commercial deployment of perovskite-based optoelectronic devices. The results presented in this work open a new route toward development of high-performance optoelectronic devices using perovskite-based hybrid nanomaterial systems.

Avalanche photodetectors based on two-dimensional layered materials

The past decade has witnessed a dramatic increase in interest in emerging photodetectors built from two-dimensional (2D) layered materials. A major driver of this trend is the growing demands for lightweight, uncooled, and even flexible photodetection technology. However, 2D layered materials always suffer from low light absorption coefficients due to their atomically thin nature. Impact ionization, which can achieve carrier multiplication, is a promising strategy to design 2D photodetectors with high detection efficiency. In this review, typical types of photodetection mechanisms in 2D photodetectors are first summarized. We then discuss the avalanche mechanism induced by impact ionization and avalanche photodetectors based on conventional silicon and III–V compound semiconductors. Finally, a host of emerging avalanche photodetectors based on 2D materials and their van der Waals heterostructures, and their potential applications in the field of photon-counting technologies are detailed. By reviewing the recent progress and discussing challenges faced by 2D avalanche photodetectors, this review aims to provide perspectives on future research directions of 2D material-based ultrasensitive photodetectors such as single-photon detectors.

Ultrasensitive polarized-light photodetectors based on 2D hybrid perovskite ferroelectric crystals with a low detection limit

Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications. Two-dimensional (2D) hybrid perovskite ferroelectrics, in which the coupling of spontaneous polarization (Ps) and light favors the dissociation of photo-induced carriers, have taken a booming position within this portfolio. However, polarized-light photodetectors with a low detection-limit remain unexplored in this 2D ferroelectric family. In this work, the high-quality individual crystals of a 2D perovskite ferroelectric, BA2CsPb2Br7 (1, where BA+ is n-butylammonium), were used to fabricate ultrasensitive polarized-light detectors. Its unique bilayered structural motif results in quite strong electric and optical anisotropy with a large absorption ratio of αc/αa ≈ 3.2 (λ = 405 nm). Besides, the presence of ferroelectric Ps also endows high built-in electric field along the polar c-axis that favors photoelectric activities. Under an extremely low detectable limit of 40 nW/cm2, the detector of 1 exhibits a notable dichroism ratio (Iphc/Ipha ≈ 1.5), a large responsivity of ~39.5 mA/W and a specific detectivity of ~1.2 × 1012 Jones. Moreover, crystal-based devices of 1 also exhibit a fast response speed (~300 μs) and excellent anti-fatigue merits. This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.

Observation of two-level defect system in amorphous Se superlattices

Amorphous Se is a well-known photoconductor from its early applications in xerography and ultra-sensitive photodetectors like the High-gain Avalanche Rushing Photoconductor (HARP) device. The established way of fabricating the photoconductor for the HARP is rotational thermal evaporation using multilayers of Se and As2Se3. However, the electronic effects of multilayering have not yet been clarified. In this report, we investigated the multilayer structure as a superlattice of Se and As2Se3 fabricated using rotational evaporation and show that the superlattice structure results in the uniformization of the defect levels in the base materials. We found four energy levels associated with defects in As2Se3 and three levels in amorphous Se. In comparison, the superlattice structure of the two materials shows two clear energy levels at EC,Se − 0.533 eV and EV,Se + 0.269 eV. The resulting two occupied energy levels explain the photoelectronic and transport properties observed in multilayer amorphous Se. This result “reinvents” the multilayer structure as a material with observed quantum effects, which significantly improves the material performance in photodetection.

Ultrasensitive Photodetectors: Ultrahigh Responsivity Photodetectors of 2D Covalent Organic Frameworks Integrated on Graphene (Adv. Mater. 9/2020)

Ultrasensitive Photodetectors: Ultrahigh Responsivity Photodetectors of 2D Covalent Organic Frameworks Integrated on Graphene (Adv. Mater. 9/2020)

Out‐of‐Plane Homojunction Enabled High Performance SnS2 Lateral Phototransistor

Abstract2D materials have been extensively applied in electronic and optoelectronic devices due to their unique and extraordinary electrical and optical properties. Among them, tin disulfide (SnS2) has attracted enormous research interests due to its low‐cost, earth‐abundant, environment friendly properties as well as superior performance in photodetectors. Here, an outstanding in‐plane SnS2 phototransistor with an out‐of‐plane built‐in electric field enabled by molybdenum oxide (MoO3) surface functionalization is demonstrated. The photocarriers are generated and effectively separated by the vertical electric field, leading to a high photoresponsivity of 2.3 × 103 A⋅W−1, photoconductive gain of >105, external quantum efficiency exceeding 8%. It also demonstrates a low noise power density, revealing an ultrasensitive photodetection with specific detectivity up to 3.2 × 1012 Jones. The formation of the out‐of‐plane built‐in electric field is validated by the output electrical transport measurement of SnS2 vertical transistor, and further corroborated by in situ ultraviolet photoelectron spectroscopy and X‐ray photoelectron spectroscopy characterizations. The findings promise surface functionalization as an effective approach to induce an internal electric field in 2D multilayer SnS2 towards its application in high performance photodetection.

Ultrasensitive and high gain solution-processed perovskite photodetectors by CH3NH3PbI2.55Br0.45:Zn2SnO4 bulk heterojunction composite

Hybrid perovskite photodetectors, the novel alternative devices transform incident light into electrical signal, have been rapidly developed in the past years. However, intrinsic unbalanced charge carrier transport within hybrid perovskite materials, restricting further boosting device performance of perovskite photodetectors, has rarely been addressed. In this study, we report room temperature–operated solution-processed bulk heterojunction perovskite photodetectors with ultrahigh sensitivity and great photo-gain. It is found that the introduction of Zn2SnO4 nanoparticles into CH3NH3PbI2.55Br0.45 perovskites results in enlarged photocurrent and suppressed dark current for bulk heterojunction perovskite photodetectors. As a result, a responsivity of over 1500 mAW−1 and projected detectivity of approximatively 1014 Jones (1 Jones = cm Hz1/2 W−1) from 380 to 760 nm are observed from bulk heterojunction perovskite photodetectors. In addition, bulk heterojunction perovskite photodetectors exhibit an excellent linear dynamic range of 124 dB and a great photo-gain of 535. All these results indicate that high-performance perovskite photodetectors could be realized through novel bulk heterojunction device structure.

Ultrahigh Responsivity Photodetectors of 2D Covalent Organic Frameworks Integrated on Graphene

2D materials exhibit superior properties in electronic and optoelectronic fields. The wide demand for high-performance optoelectronic devices promotes the exploration of diversified 2D materials. Recently, 2D covalent organic frameworks (COFs) have emerged as next-generation layered materials with predesigned π-electronic skeletons and highly ordered topological structures, which are promising for tailoring their optoelectronic properties. However, COFs are usually produced as solid powders due to anisotropic growth, making them unreliable to integrate into devices. Here, by selecting tetraphenylethylene monomers with photoelectric activity, elaborately designed photosensitive 2D-COFs with highly ordered donor-acceptor topologies are in situ synthesized on graphene, ultimately forming COF-graphene heterostructures. Ultrasensitive photodetectors are successfully fabricated with the COFETBC-TAPT -graphene heterostructure and exhibited an excellent overall performance with a photoresponsivity of ≈3.2 × 107 A W-1 at 473 nm and a time response of ≈1.14 ms. Moreover, due to the high surface area and the polarity selectivity of COFs, the photosensing properties of the photodetectors can be reversibly regulated by specific target molecules. The research provides new strategies for building advanced functional devices with programmable material structures and diversified regulation methods, paving the way for a generation of high-performance applications in optoelectronics and many other fields.

Layered-Perovskite Nanowires with Long-Range Orientational Order for Ultrasensitive Photodetectors.

2D layered metal-halide perovskites combine efficient exciton radiative recombination in crystal interior with long-distance free-carrier conduction at layer edges, which are promising candidates for realizing high-performance photovoltaic, light-emission and photodetection devices. The anisotropic electrical conductivity in layered perovskites imposes an additional requirement of orientational control for enabling favorable charge transport. However, rational fabrication of single-crystalline nanostructures with pure crystallographic orientation is still elusive. Herein, large-scale pure (101)-orientated 2D-perovskite single-crystalline nanowire arrays are realized by combining solvent engineering with the capillary-bridge lithography technique. Ordered nucleation at liquid-air interface and unidirectional growth along the dewetting direction are demonstrated by fluorescence microscopy and grazing-incidence X-ray scattering in discrete capillary bridges. In consideration of crystal interior exhibiting high resistance arising from the serial insulating organic barriers and ultrafast dissociation of excitons to generate long-lived free carriers at layer edges, ultrasensitive photodetectors are demonstrated with average responsivity exceeding 1.1 × 104 A W-1 and detectivity exceeding 9.1 × 1015 Jones.

Ultrasensitive negative capacitance phototransistors

Sensitive photodetection is crucial for modern optoelectronic technology. Two-dimensional molybdenum disulfide (MoS2) with unique crystal structure, and extraordinary electrical and optical properties is a promising candidate for ultrasensitive photodetection. Previously reported methods to improve the performance of MoS2 photodetectors have focused on complex hybrid systems in which leakage paths and dark currents inevitably increase, thereby reducing the photodetectivity. Here, we report an ultrasensitive negative capacitance (NC) MoS2 phototransistor with a layer of ferroelectric hafnium zirconium oxide film in the gate dielectric stack. The prototype photodetectors demonstrate a hysteresis-free ultra-steep subthreshold slope of 17.64 mV/dec and ultrahigh photodetectivity of 4.75 × 1014 cm Hz1/2 W−1 at room temperature. The enhanced performance benefits from the combined action of the strong photogating effect induced by ferroelectric local electrostatic field and the voltage amplification based on ferroelectric NC effect. These results address the key challenges for MoS2 photodetectors and offer inspiration for the development of other optoelectronic devices.

An ultrasensitive self-driven broadband photodetector based on a 2D-WS2/GaAs type-II Zener heterojunction.

High-performance broadband photodetectors have attracted extensive research interest because of their significance in optoelectronic applications. In this study, a highly sensitive room-temperature (RT) broadband photodetector composed of a WS2/GaAs type-II van der Waals heterojunction was demonstrated, which exhibited obvious photoresponse to broadband light illumination from 200 to 1550 nm beyond the limitation of the bandgaps. Impressive device performances were achieved in terms of a low noise current of ∼59.7 pA, a high responsivity up to 527 mA W-1, an ultrahigh Ilight/Idark ratio of 107, a large specific detectivity of 1.03 × 1014 Jones, a minimum detection light intensity of 17 nW cm-2 and an external quantum efficiency (EQE) up to 80%. Transient photoresponse measurements revealed that the present detector is capable of working at a high frequency with a 3 dB cutoff frequency up to 10 kHz and a corresponding rise/fall time of 21.8/49.6 μs. Notably, this heterojunction device demonstrated Zener tunneling behaviors with a threshold voltage of -4 V. The capacitance-voltage (C-V) properties of the heterojunction were investigated to understand the device performances. In addition, the as-fabricated device can function as an image sensor with an outstanding imaging capability. Considering the above superior features, the proposed WS2/GaAs type-II van der Waals heterojunction may find great potential in high-performance broadband photodetection applications.