Solution‐Processed 3D RGO–MoS2/Pyramid Si Heterojunction for Ultrahigh Detectivity and Ultra‐Broadband Photodetection

Molybdenum disulfide (MoS₂), a typical 2D metal dichalcogenide (2DMD), has exhibited tremendous potential in optoelectronic device applications, especially in photodetection. However, due to the weak light absorption of planar mono‐/multilayers, limited cutoff wavelength edge, and lack of high‐quality junctions, most reported MoS₂‐based photodetectors show undesirable performance. Here, a structurized 3D heterojunction of RGO–MoS₂/pyramid Si is demonstrated via a simple solution‐processing method. Owing to the improved light absorption by the pyramid structure, the narrowed bandgap of the MoS₂ by the imperfect crystallinity, and the enhanced charge separation/transportation by the inserted reduced graphene oxide (RGO), the assembled photodetector exhibits excellent performance in terms of a large responsivity of 21.8 A W^?1, extremely high detectivity up to 3.8 × 10¹⁵ Jones (Jones = cm Hz^1/2 W^?1) and ultrabroad spectrum response ranging from 350 nm (ultraviolet) to 4.3 µm (midwave infrared). These device parameters represent the best results for MoS₂‐based self‐driven photodetectors, and the detectivity value sets a new record for the 2DMD‐based photodetectors reported thus far. Prospectively, the design of novel 3D heterojunction can be extended to other 2DMDs, opening up the opportunities for a host of high‐performance optoelectronic devices.     

Gate‐Controlled Graphene–Silicon Schottky Junction Photodetector

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate‐controlled graphene–silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈10⁴), a very high photoresponsivity (≈70 A W⁻¹), and a low dark current in the order of µA cm⁻² in a wide wavelength range (395–850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene‐field‐effect transistor‐based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.     

2D In2S3 Nanoflake Coupled with Graphene toward High‐Sensitivity and Fast‐Response Bulk‐Silicon Schottky Photodetector

Silicon‐based electronic devices, especially graphene/Si photodetectors (Gr/Si PDs), have triggered tremendous attention due to their simple structure and flexible integration of the Schottky junction. However, due to the relatively poor light–matter interaction and mobility of silicon, these Gr/Si PDs typically suffer an inevitable compromise between photoresponsivity and response speed. Herein, a novel strategy for coupling 2D In₂S₃ with Gr/Si PDs is demonstrated. The introduction of the double‐heterojunction design not only strengthens the light absorption of graphene/Si but also combines the advantages of the photogating effect and photovoltaic effect, which suppresses the dark current, accelerates the separation of photogenerated carriers, and brings photoconductive gain. As a result, In₂S₃/graphene/Si devices present an ultrahigh photoresponsivity of 4.53 × 10⁴ A W^?1 and fast response speed less than 40 µs, simultaneously. These parameters are an order of magnitude higher than pristine Gr/Si PDs and among the best values compared with reported 2D materials/Si heterojunction PDs. Furthermore, the In₂S₃/graphene/Si PD expresses outstanding long‐term stability, with negligible performance degradation even after 1 month in air or 1000 cycles of operation. These findings highlight a simple and novel strategy for constructing high‐sensitivity and ultrafast Gr/Si PDs for further optoelectronic applications.     

Enhanced sensitivity and response speed of graphene oxide/ZnO nanorods photodetector fabricated by introducing graphene oxide in seed layer

Graphene/ZnO nanocomposites photodetectors hold great potential for UV detection because of the combination of photosensitive ZnO and high electron-mobility graphene. In this paper, graphene oxide (GO)/ZnO nanorods photoconductive photodetector with seed layer of GO and ZnO nanocrystals (NCs) hybrids is fabricated via a low-cost solution process. Uniform and oriented GO/ZnO nanorods have been obtained due to the positive role of GO in the growth process of ZnO nanorods, which gives rise to less light scattering and thereby stronger absorption and enhanced photocurrent. When the growth time is 1 h, the optimum photocurrent of GO/ZnO nanorods is about 9.4 times than pure ZnO nanorods, meanwhile, the corresponding detectivity reaches 7.17?×?10¹¹ cm Hz^1/2 W^?1. In addition, owing to the high carrier mobility of graphene, the response time t ₉₀ of GO/ZnO photodetector beneficially decreases to ~1 s, which is much faster than many other GO/ZnO hybrid photodetectors.     

Graphene–Ruthenium Complex Hybrid Photodetectors with Ultrahigh Photoresponsivity

The maximum responsivity of a pure monolayer graphene‐based photodetector is currently less than 10 mA W^?1 because of small optical absorption and short recombination lifetime. Here, a graphene hybrid photodetector functionalized with a photoactive ruthenium complex that shows an ultrahigh responsivity of ≈1 × 10⁵ A W^?1 and a photoconductive gain of ≈3 × 10⁶ under incident optical intensity of the order of sub‐milliwatts is reported. This responsivity is two orders of magnitude higher than the precedent best performance of graphene‐based photodetectors under a similar incident light intensity. Upon functionalization with a 4‐nm‐thick ruthenium complex, monolayer graphene‐based photodetectors exhibit pronounced n‐type doping effect due to electron transfer via the metal?ligand charge transfer (MLCT) from the ruthenium complex to graphene. The ultrahigh responsivity is attributed to the long lifetime and high mobility of the photoexcited charge carriers. This approach is highly promising for improving the responsivity of graphene‐based photodetectors.     

Highly Sensitive,Fast Response Perovskite Photodetectors Demonstrated in Weak Light Detection Circuit and Visible Light Communication System

Organic–inorganic hybrid perovskite (OIHP) photodetectors have presented unprecedented device performance mainly owing to outstanding material properties. However, the solution‐processed OIHP polycrystalline thin films with defective surface and grain boundaries always impair the key parameter of photodetectors. Herein, a nonfullerene passivation layer exhibits more efficient passivation for OIHP materials to dramatically reduce the trap density of state, yielding a dark current as low as 2.6 × 10^?8 A cm^?2 under ?0.1 V. In addition, the strong absorption in near‐infrared (NIR) region of nonfullerene/C₆₀ heterojunction broadens the detectable range to over 900 nm by effective charge transport, ultimately leading to a specific detectivity of 1.45 × 10¹² and 7.37 × 10¹¹ cm Hz^1/2 W^?1 at 650 and 820 nm, respectively. Encouragingly, the response speed of 27 ns is obtained at 0.6 mm² of device area by removing constrain from the resistance–capacitance constant. Moreover, the prominent practical application of the photodetector is demonstrated in a weak light detection circuit and a visible light communication system. It is believed that the OIHP photodetectors with high sensitivity, NIR photoresponse, and ultrafast speed would pave the way to commercial applications.     

Superior Performances of Self-Driven Near-Infrared Photodetectors Based on the SnTe:Si/Si Heterostructure Boosted by Bulk Photovoltaic Effect (Small 14/2023)

The upsurge of new materials that can be used for near-infrared (NIR) photodetectors operated without cooling is crucial. As a novel material with a small bandgap of ≈0.28 eV, the topological crystalline insulator SnTe has attracted considerable attention. Herein, this work demonstrates self-driven NIR photodetectors based on SnTe/Si and SnTe:Si/Si heterostructures. The SnTe/Si heterostructure has a high detectivity D* of 3.3 × 10¹² Jones. By Si doping, the SnTe:Si/Si heterostructure reduces the dark current density and increases the photocurrent by ≈1 order of magnitude simultaneously, which improves the detectivity D* by ≈2 orders of magnitude up to 1.59 × 10¹⁴ Jones. Further theoretical analysis indicates that the improved device performance may be ascribed to the bulk photovoltaic effect (BPVE), in which doped Si atoms break the inversion symmetry and thus enable the generation of additional photocurrents beyond the heterostructure. In addition, the external quantum efficiency (EQE) measured at room temperature at 850 nm increases by a factor of 7.5 times, from 38.5% to 289%. A high responsivity of 1979 mA W⁻¹ without bias and fast rising time of 8 µs are also observed. The significantly improved photodetection achieved by the Si doping is of great interest and may provide a novel strategy for superior photodetectors.     

Ferroelectric Localized Field–Enhanced ZnO Nanosheet Ultraviolet Photodetector with High Sensitivity and Low Dark Current

Zinc oxide (ZnO) nanosheets have demonstrated outstanding electrical and optical properties, which are well suited for ultraviolet (UV) photodetectors. However, they have a high density of intrinsically unfilled traps, and it is difficult to achieve p‐type doping, leading to the poor performance for low light level switching ratio and a high dark current that limit practical applications in UV photodetection. Here, UV photodetectors based on ZnO nanosheets are demonstrated, whose performance is significantly improved by using a ferroelectric localized field. Specifically, the photodetectors have achieved a responsivity of up to 3.8 × 10⁵ A W^?1, a detectivity of 4.4 × 10¹⁵ Jones, and a photocurrent gain up to 1.24 × 10⁶. These device figures of merit are far beyond those of traditional ZnO ultraviolet photodetectors. In addition, the devices' initial dark current can be easily restored after continuous photocurrent measurement by using a positive gate voltage pulse. This study establishes a new approach to produce high‐sensitivity and low‐dark‐current ultraviolet photodetectors and presents a crucial step for further practical applications.     

All-Oxide Transparent Photodetector Array for Ultrafast Response through Self-Powered Excitonic Photovoltage Operation

Can photodetectors be transparent and operate in self-powered mode? Is it possible to achieve invisible electronics, independent of the external power supply system, for on-site applications? Here, a ZnO/NiO heterojunction-based high-functional transparent ultraviolet (UV) photodetector operating in the self-powered photovoltaic mode with outstanding responsivity and detectivity values of 6.9 A W⁻¹ and 8.0 × 10¹² Jones, respectively, is reported. The highest I_UV/I_dark value of 8.9 × 10⁴ is attained at a wavelength of 385 nm, together with a very small dark current value of 9.15 × 10⁻¹² A. A large-scale sputtering method is adopted to deposit the heterostructure of n-ZnO and p-NiO sequentially. This deposition instinctively forms an abrupt junction, resulting in a high-quality heterojunction device. Moreover, developing a ZnO/NiO-heterojunction–based 4 × 5 matrix array with an output photovoltage of 4.5 V is preferred for integrating photodetectors into sensing and imaging systems. This transparent UV photodetector exhibits the fastest photo-response time (83 ns) reported for array configurations, which is achieved using an exciton-induced photovoltage based on a neutral donor–bound exciton. Overall, this study provides a simple method for achieving a high-performance large-scale transparent UV photodetector with a self-powered array configuration.     

Gradient Energy Band Driven High‐Performance Self‐Powered Perovskite/CdS Photodetector

Self‐powered photodetectors are highly desired to meet the great demand in applications of sensing, communication, and imaging. Manipulating the carrier separation and recombination is critical to achieve high performance. In this paper, a self‐powered photodetector based on the integrated gradient O‐doped CdS nanorod array and perovskite is presented. Through optimizing the degree of continuous built‐in band bending in the gradient‐O CdS, the photodetector demonstrates a remarkable detectivity of 2.1 × 10¹³ Jones. Under the self‐powered voltage mode, the responsivity can be as high as 0.48 A W^?1, and the rise and decay time are 0.54/2.21 ms. The comprehensive performance is comparable and even better than reported perovskite and other types of self‐powered photodetectors. The improved mechanism reveals that the gradient band bending promotes the photogenerated carrier transfer and hinders the recombination at the interface.     

High‐Responsivity Photodetection by a Self‐Catalyzed Phase‐Pure p‐GaAs Nanowire

Defects are detrimental for optoelectronics devices, such as stacking faults can form carrier‐transportation barriers, and foreign impurities (Au) with deep‐energy levels can form carrier traps and nonradiative recombination centers. Here, self‐catalyzed p‐type GaAs nanowires (NWs) with a pure zinc blende (ZB) structure are first developed, and then a photodetector made from these NWs is fabricated. Due to the absence of stacking faults and suppression of large amount of defects with deep energy levels, the photodetector exhibits room‐temperature high photoresponsivity of 1.45 × 10⁵ A W^?1 and excellent specific detectivity (D*) up to 1.48 × 10¹⁴ Jones for a low‐intensity light signal of wavelength 632.8 nm, which outperforms previously reported NW‐based photodetectors. These results demonstrate these self‐catalyzed pure‐ZB GaAs NWs to be promising candidates for optoelectronics applications.     

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2/Te Tunneling Heterostructure

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2D photodetectors is still below the requirements for practical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS₂/Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W⁻¹, an outstanding detectivity of 9.28 × 10¹³ Jones, a fast rise/decay time of 1.7/3.2 ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.     

Growth of Ultraflat PbI2 Nanoflakes by Solvent Evaporation Suppression for High‐Performance UV Photodetectors

2D lead iodide (PbI₂) is attracting great interest due to its great potential in the application of UV photodetectors. In this work, a facile solution‐based method is developed to synthesize ultraflat PbI₂ nanoflakes for high‐performance UV photodetectors. By maintaining at proximate room temperature and adding an evaporation suppression solvent for slow‐rate crystal growth, high‐quality PbI₂ nanoflakes with an ultraflat surface are obtained. The UV photodetectors based on 2D PbI₂ nanoflakes exhibit a high photoresponsivity of 0.51 A W^?1, a high detectivity of 4.0 × 10¹⁰ Jones, a high external quantum efficiency (EQE) of 168.9%, and a rapid response speed including a rise time of 14.1 ms and a decay time of 31.0 ms. The balanced and excellent photodetector performance of these devices paves the road for practical UV photodetection based on 2D PbI₂ nanoflakes.     

Light Confinement Effect Induced Highly Sensitive,Self‐Driven Near‐Infrared Photodetector and Image Sensor Based on Multilayer PdSe2/Pyramid Si Heterojunction

In this study, a highly sensitive and self‐driven near‐infrared (NIR) light photodetector based on PdSe₂/pyramid Si heterojunction arrays, which are fabricated through simple selenization of predeposited Pd nanofilm on black Si, is demonstrated. The as‐fabricated hybrid device exhibits excellent photoresponse performance in terms of a large on/off ratio of 1.6 × 10⁵, a responsivity of 456 mA W^?1, and a high specific detectivity of up to 9.97 × 10¹³ Jones under 980 nm illumination at zero bias. Such a relatively high sensitivity can be ascribed to the light trapping effect of the pyramid microstructure, which is confirmed by numerical modeling based on finite‐difference time domain. On the other hand, thanks to the broad optical absorption properties of PdSe₂, the as‐fabricated device also exhibits obvious sensitivity to other NIR illuminations with wavelengths of 1300, 1550, and 1650 nm, which is beyond the photoresponse range of Si‐based devices. It is also found that the PdSe₂/pyramid Si heterojunction device can also function as an NIR light sensor, which can readily record both “tree” and “house” images produced by 980 and 1300 nm illumination, respectively.     

Highly Efficient and Ultrasensitive Large‐Area Flexible Photodetector Based on Perovskite Nanowires

Hybrid organic–inorganic perovskites have shown exceptional semiconducting properties and microstructural versatility for inexpensive, solution‐processable photovoltaic and optoelectronic devices. In this work, an all‐solution‐based technique in ambient environment for highly sensitive and high‐speed flexible photodetectors using high crystal quality perovskite nanowires grown on Kapton substrate is presented. At 10 V, the optimized photodetector exhibits a responsivity as high as 0.62 A W^?1, a maximum specific detectivity of 7.3 × 10¹² cm Hz^1/2 W^?1, and a rise time of 227.2 µs. It also shows remarkable photocurrent stability even beyond 5000 bending cycles. Moreover, a deposition of poly(methyl methacrylate) (PMMA) as a protective layer on the perovskite yields significantly better stability under ambient air operation: the PMMA‐protected devices are stable for over 30 days. This work demonstrates a cost‐effective fabrication technique for high‐performance flexible photodetectors and opens opportunities for research advancements in broadband and large‐scale flexible perovskite‐based optoelectronic devices.     

High Detectivity and Transparent Few‐Layer MoS2/Glassy‐Graphene Heterostructure Photodetectors

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two‐dimensional (2D) components and imparted from their interactions. Here, a novel few‐layer MoS₂/glassy‐graphene heterostructure, synthesized by a layer‐by‐layer transfer technique, and its application as transparent photodetectors are reported for the first time. Instead of a traditional Schottky junction, coherent ohmic contact is formed at the interface between the MoS₂ and the glassy‐graphene nanosheets. The device exhibits pronounced wavelength selectivity as illuminated by monochromatic lights. A responsivity of 12.3 mA W^?1 and detectivity of 1.8 × 10¹⁰ Jones are obtained from the photodetector under 532 nm light illumination. Density functional theory calculations reveal the impact of specific carbon atomic arrangement in the glassy‐graphene on the electronic band structure. It is demonstrated that the band alignment of the layered heterostructures can be manipulated by lattice engineering of 2D nanosheets to enhance optoelectronic performance.     

A High-Performance Solution-Processed Organic Photodetector for Near-Infrared Sensing

Sensitive detection of near-infrared (NIR) light enables many important applications in both research and industry. Current organic photodetectors suffer from low NIR sensitivity typically due to early absorption cutoff, low responsivity, and/or large dark/noise current under bias. Herein, organic photodetectors based on a novel ultranarrow-bandgap nonfullerene acceptor, CO1-4Cl, are presented, showcasing a remarkable responsivity over 0.5 A W⁻¹ in the NIR spectral region (920–960 nm), which is the highest among organic photodiodes. By effectively delaying the onset of the space charge limited current and suppressing the shunt leakage current, the optimized devices show a large specific detectivity around 10¹² Jones for NIR spectral region up to 1010 nm, close to that of a commercial Si photodiode. The presented photodetectors can also be integrated in photoplethysmography for real-time heart-rate monitoring, suggesting its potential for practical applications.     

Asymmetrically Encapsulated Vertical ITO/MoS2/Cu2O Photodetector with Ultrahigh Sensitivity

Strong light absorption, coupled with moderate carrier transport properties, makes 2D layered transition metal dichalcogenide semiconductors promising candidates for low intensity photodetection applications. However, the performance of these devices is severely bottlenecked by slow response with persistent photocurrent due to long lived charge trapping, and nonreliable characteristics due to undesirable ambience and substrate effects. Here ultrahigh specific detectivity (D*) of 3.2 × 10¹⁴ Jones and responsivity (R) of 5.77 × 10⁴ A W^?1 are demonstrated at an optical power density (P_op) of 0.26 W m^?2 and external bias (V_ext) of ?0.5 V in an indium tin oxide/MoS₂/copper oxide/Au vertical multi‐heterojunction photodetector exhibiting small carrier transit time. The active MoS₂ layer being encapsulated by carrier collection layers allows us to achieve repeatable characteristics over large number of cycles with negligible trap assisted persistent photocurrent. A large D* > 10¹⁴ Jones at zero external bias is also achieved due to the built‐in field of the asymmetric photodetector. Benchmarking the performance against existing reports in literature shows a viable pathway for achieving reliable and highly sensitive photodetectors for ultralow intensity photodetection applications.     

Large-Area Black Phosphorus/PtSe2 Schottky Junction for High Operating Temperature Broadband Photodetectors

High operating temperature (HOT) broadband photodetectors are urgently necessary for extreme condition applications in infrared-guided missiles, infrared night vision, fire safety imaging, and space exploration sensing. However, conventional photodetectors show dramatic carrier mobility decreases and carrier losses with low photoresponsivity at HOT due to the increased carrier scattering in channels at high temperatures. Herein, the HOT broadband photodetectors from room temperature to 470 K are developed for the first time by large-area black phosphorus (BP)/PtSe₂ films device arrays via a depletion-enhanced photocarrier dynamics strategy. Attributed to the 2D Schottky junction at BP/PtSe₂ interface and resulting in full depleted working channels, the BP/PtSe₂ photodetector arrays exhibit high tolerance to carrier mobility decrease during the increasing operating temperature in a wide wavelength range from 532 to 2200 nm. Thus, the photodetector shows a state-of-the-art operating temperature at 470 K with the photo-responsivity (R) and specific detectivity (D*) of 25 A W⁻¹ and 6.4 × 10¹¹ Jones under 1850 nm illumination, respectively. Moreover, BP/PtSe₂ photodetector arrays show high-uniformity photo-response in a large area. This work provides new strategies for high-performance broadband photodetector arrays with HOT by Schottky junction of large-area BP/PtSe₂ films.     

Disentangling the Role of the SnO Layer on the Pyro-Phototronic Effect in ZnO-Based Self-Powered Photodetectors

Self-powered photodetectors (PDs) have been recognized as one of the developing trends of next-generation optoelectronic devices. Herein, it is shown that by introducing a thin layer of SnO film between the Si substrate and the ZnO film, the self-powered photodetector Al/Si/SnO/ZnO/ITO exhibits a stable and uniform violet sensing ability with high photoresponsivity and fast response. The SnO layer introduces a built-in electrostatic field to highly enhance the photocurrent by over 1000%. By analyzing energy diagrams of the p-n junction, the underlying physical mechanism of the self-powered violet PDs is carefully illustrated. A high photo-responsivity (R) of 93 mA W⁻¹ accompanied by a detectivity (D*) of 3.1 × 10¹⁰ Jones are observed under self-driven conditions, when the device is exposed to 405 nm excitation laser wavelength, with a laser power density of 36 mW cm⁻² and at a chopper frequency of 400 Hz. The Si/SnO/ZnO/ITO device shows an enhancement of 3067% in responsivity when compared to the Al/Si/ZnO/ITO. The photodetector holds an ultra-fast response of ≈ 2 µs, which is among the best self-powered photodetectors reported in the literature based on ZnO.