Excellent Detectivity Research Articles

Self-powered high-performance topological crystalline insulators tin selenide/silicon dioxide/silicon heterojunction broadband photodetectors for weak signal detection

Abstract Topological crystalline insulators have been demonstrated to possess a broadband absorption spectrum owing to the gapless topological surface states and narrow bulk band gap, which are promising candidates for new generation optoelectronic devices application. Herein, we fabricated a high-quality topological crystalline insulator tin selenide (SnSe)/SiO 2 /Si heterostructure using a simple magnetron sputtering method. Our strategy is to build high-quality heterojunctions on silicon wafers by directly growing films to achieve sufficiently large interfacial barriers, enhance the photovoltaic effect of heterojunctions, and make heterojunctions achieve better photo response characteristics. At zero voltage, the current of heterojunction varies from extremely low dark current (∼10 −10 A) to high photocurrent (∼10 −5 A). These advantages make the SnSe/SiO 2 /Si heterostructure show a superior photoresponsivity of 39.2 AW −1 , an excellent detectivity ( D* ) of 4.2 × 10 16 cmHz 1/2 W −1 , a large broadband photoresponse from 365 nm–980 nm and a fast response speed of approximately microseconds. The over-all properties have greatly exceeded those of the reported 2D-based vertical VDW heterojunctions, those 2D film/Si heterojunctions and other Topological insulators/Si heterojunctions photodetectors respecting D* , on-off ratio, bandwidth etc. The SnSe/SiO 2 /Si heterojunctions will provide more chance for future optoelectronic devices applications.

Ultrasensitive flexible near-infrared photodetectors based on Van der Waals Bi2Te3 nanoplates

As an emerging two-dimensional (2D) material, Bi2Te3 has exhibited great potential for the applications in electronic and optoelectronic devices due to its unique features as topological insulator and thus high electron mobility. However, the application of 2D Bi2Te3 nanostructures in flexible NIR (near infrared) photodetectors has barely been investigated. In this work, we present a study on NIR photodetectors based on 2D Bi2Te3 nanoplates, which are grown on mica substrates by Van der Waals epitaxy (vdWe) method. The vertical thickness of the Bi2Te3 nanoplates is as small as 12 nm, while the lateral size is as large as 18 μm. The flexible NIR photodetectors based on the 2D Bi2Te3 nanoplates present excellent device performance, including photoresponsivity, specific detectivity and photoconductive gain. Under the illumination of a NIR laser (an emission wavelength of 850 nm), the photoresponsivity, specific detectivity and photoconductive gain are determined to be up to 55.06 mA/W, 8.05 × 10−2 and 5.92 × 107 Jones, respectively. In addition, the device performance (photoresponsivity, detectivity, rising time and decay time) of the Bi2Te3 nanoplate photodetectors shows no obvious degradation after bending for 100 times and 300 times, indicating the great flexibility of the photodetectors based on Bi2Te3 nanoplates. These findings indicate that Bi2Te3 nanoplates have great potential for fabricating flexible NIR detectors with high detectivity and photoresponsivity.

High-Performance Organic Phototransistors With Vertical Structure Design

In this paper, a novel vertical phototransistor was reported and compared with planar phototransistors for the first time. As compared with the planar phototransistors, the vertical ones exhibited much better photoelectric performance, which is attributed to an ultrashort photo-generated holes transfer distance and a stronger excitons dissociating electrical field due to their ultrashort channel length (tens of nanometers). Moreover, in order to examine the transport and trapping of different carrier charges separately, the impact of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) dopant on the performance of planar and vertical phototransistors was investigated. The vertical devices exhibited an ultrahigh responsivity (~6600 A/W) as well as an excellent detectivity ( $\sim 7\times 10^{15}~\text{Jones}$ ) and a fast photoresponse (rise time of 0.28 s), whereas slight changes were observed in the planar ones with doping of PCBM. The high performance of the blend vertical phototransistors is due to the trapping of the photo-generated electrons with PCBM and the effective transport of holes due to the ultrashort channel length. This paper provided a promising pathway for low-cost, high-performance phototransistors.

Confined van der Waals Epitaxial Growth of Two-Dimensional Large Single-Crystal In2Se3 for Flexible Broadband Photodetectors

The controllable growth of two-dimensional (2D) semiconductors with large domain sizes and high quality is much needed in order to reduce the detrimental effect of grain boundaries on device performance but has proven to be challenging. Here, we analyze the precursor concentration on the substrate surface which significantly influences nucleation density in a vapor deposition growth process and design a confined micro-reactor to grow 2D In2Se3 with large domain sizes and high quality. The uniqueness of this confined micro-reactor is that its size is ~102-103 times smaller than that of a conventional reactor. Such a remarkably small reactor causes a very low precursor concentration on the substrate surface, which reduces nucleation density and leads to the growth of 2D In2Se3 grains with sizes larger than 200 μm. Our experimental results show large domain sizes of the 2D In2Se3 with high crystallinity. The flexible broadband photodetectors based on the as-grown In2Se3 show rise and decay times of 140 ms and 25 ms, efficient response (5.6 A/W), excellent detectivity (7×1010 Jones), high external quantum efficiency (251%), good flexibility, and high stability. This study, in principle, provides an effective strategy for the controllable growth of high quality 2D materials with few grain boundaries.

All-in-One Porous Polymer Adsorbents with Excellent Environmental Chemosensory Responsivity, Visual Detectivity, Superfast Adsorption, and Easy Regeneration.

It remains a formidable challenge to construct advanced adsorbents with superb adsorption, environmental stimuli response, and real-time detection capability for efficiently treating contaminants from complex environmental systems. A novel class of an all-in-one microporous adsorbent that simultaneously has excellent environmental chemosensory responsivity, visual detectivity, superfast micropollutant adsorption, as well as easy regeneration is reported herein. The advanced microporous adsorbent discussed in this study presents a hairy nanospherical morphology composed of a hairy stimuli-responsive polymeric shell and a shell-assisted superadsorptive microporous core. The adsorbent not only exhibits a valuable capability of pollutant detection by visible fluorescence quenching, but can also remove organic micropollutants from polluted water with super-rapid speed (79%, 98%, and 100% of its equilibrium uptake in 7 s, 10 s, and 2 min, respectively) and excellent recyclability (>96%). More importantly, the adsorbent still shows unimpeded adsorption performance in the flow-through adsorption tests (15 mL min-1 ), indicating a very appealing application prospect.

Confined van der Waals Epitaxial Growth of Two-Dimensional Large Single-Crystal In2Se3 for Flexible Broadband Photodetectors.

The controllable growth of two-dimensional (2D) semiconductors with large domain sizes and high quality is much needed in order to reduce the detrimental effect of grain boundaries on device performance but has proven to be challenging. Here, we analyze the precursor concentration on the substrate surface which significantly influences nucleation density in a vapor deposition growth process and design a confined micro-reactor to grow 2D In2Se3 with large domain sizes and high quality. The uniqueness of this confined micro-reactor is that its size is ~102-103 times smaller than that of a conventional reactor. Such a remarkably small reactor causes a very low precursor concentration on the substrate surface, which reduces nucleation density and leads to the growth of 2D In2Se3 grains with sizes larger than 200 μm. Our experimental results show large domain sizes of the 2D In2Se3 with high crystallinity. The flexible broadband photodetectors based on the as-grown In2Se3 show rise and decay times of 140 ms and 25 ms, efficient response (5.6 A/W), excellent detectivity (7×1010 Jones), high external quantum efficiency (251%), good flexibility, and high stability. This study, in principle, provides an effective strategy for the controllable growth of high quality 2D materials with few grain boundaries.

Dip-coated colloidal quantum-dot films for high-performance broadband photodetectors

Homogeneous large-area QD films were obtained by a dip-coating method. Photodetectors assembled with these films possess excellent detectivity.

Visible-infrared dual-mode MoS2-graphene-MoS2 phototransistor with high ratio of the Iph/Idark

2D materials such as graphene and transition metal dichalcogenides exhibit novel electrical and optoelectrical properties, which are promising for the application in sensing and imaging. However, the photoresponse ability of pure monolayer graphene in room temperature and ratio of Iph and Idark are still unsatisfactory, due to the weak light absorption itself, short lifetime of photo-excited carriers and large dark current, especially in the infrared range. Here, we successfully constructed a broadband graphene-based phototransistor consisting of lateral MoS2-graphene-MoS2 heterostructure by chemical vapor deposition technique. It shows broadband photodetection and a low dark current less than 1 pA at applied bias of 0.5 V, resulting in excellent specific detectivity more than 1012 Jones and nearly 109 Jones in visible and infrared band, respectively. Moreover, the ratio of Iph and Idark could be modulated by the back-gate voltage when the phototransistor is under the infrared illumination. And a high ratio of 105 was exhibited. This type of graphene-based phototransistor by chemical vapor deposition demonstrates an approach for the room temperature broadband photodetection of monolayer graphene by energy engineering. All the results address key challenges for broadband detection by graphene-based phototransistor, and are promising for the large scale fabrication and integration in the future electronic and optoelectronic applications.

Low-temperature-gradient crystallization for multi-inch high-quality perovskite single crystals for record performance photodetectors

With their excellent optoelectronic properties, the practical application of single-crystalline organolead halide perovskite materials is now limited by the lack of a method to prepare high-quality perovskite single crystals in large dimension. Herein, we report our development of a low-temperature-gradient crystallization (LTGC) method for high-quality CH 3 NH 3 PbBr 3 (MAPbBr 3 ) perovskite single crystals with lateral dimension as large as two inches. The theoretical analysis suggests that a small temperature gradient should be used to restrain the growth condition, particularly the solution concentration, within the optimal single-crystal-growth (OSCG) zone. The solubility curve as a function of temperature reveals a sharp turning point at ∼60 °C, across which the first-order solubility derivative (dC/dT) shows very different behaviors: below this temperature, the dC/dT changes dramatically as the temperature increases, while above this temperature, the dC/dT enters a plateau where further temperature change has little effect on the derivative, meaning that one can attain both a substantial crystal growth rate and crystallization yield below this temperature. Utilizing this discovery, a MAPbBr 3 single crystal as large as 47 × 41 × 14 mm is obtained with high quality via the LTGC method. The single crystal exhibits the best optoelectronic quality among all MAPbBr 3 materials reported in the literature, including the best trap state density, mobility, carrier lifetime, and diffusion length. These superior optoelectronic properties are further transferred into a high-performance planar photodetector. The device exhibits high operational stability, high external quantum efficiency (13,453%), excellent detectivity as high as 8 × 10 13 Jones, and a fast response speed as quick as 15.8 μs. To our knowledge, both the detectivity and the response speed are the best among all MAPbBr 3 devices reported to date. The unique synthesis method and excellent crystalline quality of the perovskite single crystals make them promising candidates for the next generation of optoelectronic devices.

High Detectivity from a Lateral Graphene–MoS2 Schottky Photodetector Grown by Chemical Vapor Deposition

Abstract2D material–based photodetectors have demonstrated the great potential in future optoelectric applications and the compatibility with the traditional semiconductor technology. However, low detectivity and difficulty of large‐scale fabrication still limit their application. Here, an ultrasensitive in‐plane lateral graphene–MoS2 heterostructure is successfully constructed using one‐step growth by chemical vapor deposition, which is suitable for large‐scale fabrication. The Schottky junction is formed in the channel with the edge contact of graphene and MoS2. It displays good rectification characteristics with an on/off ratio up to 106. As a photodetector, it exhibits excellent detectivity with the specific detectivity D* up to 1.4 × 1014 Jones and the responsivity of 1.1 × 105 A W−1, which benefit from strong absorption, the efficient separation of the photoexcited carriers, and quick charge transport in the Schottky junction device. Moreover, heterostructure photodetector array is demonstrated here which shows the large‐scale fabrication capacity. All of these results prove the potential of 2D material–based junction devices for optoelectronic devices.

High-Performance Near-Infrared Photodetectors Based on p-Type SnX (X = S, Se) Nanowires Grown via Chemical Vapor Deposition.

Because of the distinct electronic properties and strong interaction with light, quasi-one-dimensional nanowires (NWs) with semiconducting property have been demonstrated with tremendous potential for various technological applications, especially electronics and optoelectronics. However, until now, most of the state-of-the-art NW photodetectors are predominantly based on the n-type NW channel. Here, we successfully synthesized p-type SnSe and SnS NWs via the chemical vapor deposition method and fabricated high-performance single SnSe and SnS NW photodetectors. Importantly, these two NW devices exhibit an impressive photodetection performance with a high photoconductive gain of 1.5 × 104 (2.8 × 104), good responsivity of 1.0 × 104 A W-1 (1.6 × 104 A W-1), and excellent detectivity of 3.3 × 1012 Jones (2.4 × 1012 Jones) under near-infrared illumination at a bias of 3 V for the SnSe NW (SnS NW) channel. The rise and fall times can be as efficient as 460 and 520 μs (1.2 and 15.1 ms), respectively, for the SnSe NW (SnS NW) device. Moreover, the spatially resolved photocurrent mapping of the devices further reveals the bias-dependent photocurrent generation. All these results evidently demonstrate that the p-type SnSe and SnS NWs have great potential to be applied in next-generation high-performance optoelectronic devices.

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.

Broadband surface plasmon resonance enhanced self-powered graphene/GaAs photodetector with ultrahigh detectivity

A type of broadband (325−980 nm) self-powered photodetector based on graphene/GaAs van der Waals heterojunction is reported. By simply spinning a layer of Ag nano-particles (Ag NPs) onto graphene/GaAs heterostructure, the responsivity and detectivity of our devices for the whole spectrum range are enhanced significantly. The maximum photocurrent responsivity of 210 mA W−1 (increased by 38%) and detectivity of 2.98 × 1013 Jones (increased by 202%) are achieved at 405 nm, which is about two or three orders of magnitude larger than other graphene based self-powered photodetectors. The mechanism of the improvement originates from the overlap the depletion region of graphene/GaAs heterostructure, the surface plasmon enhanced light field region below the surface and the light absorption region of the GaAs layer. The external quantum efficiency (EQE) measurement, transient photoluminescence (PL) test and the comparative theoretical simulation show that the surface plasmon enhancement should only be applicable for graphene/direct band gap semiconductor heterostructure, where the semiconductor should have a high optical absorption coefficient. The obtained high performance broadband photodetector with excellent detectivity is a promising candidate for many important optoelectronic applications, such as ultrasensitive image sensor in charge coupled displayer field, which requires colour sensors not only with high photo responsivity but also in a wide spectral range.

Tellurophene-Based Random Copolymers for High Responsivity and Detectivity Photodetectors.

Organic photodetectors (OPDs) have attracted great attention because of their advantages including tunable response range, easy processability, and flexibility. Various conjugated polymers have been developed for high-performing OPDs. Herein, a series of tellurophene-based random copolymers containing two typical electron-withdrawing units naphthalene diimide (NDI) and perylene diimide (PDI) are designed and synthesized. Through varying the ratio of PDI/NDI moieties of the analogous polymers, the optophysical properties and film morphology, together with photodetector performances, are systematically tuned. It was demonstrated that the photodetectors based on the polymer with the molar ratio of PDI/NDI units of 70/30 possessed strong photoinduced absorption and favorable morphology via transient absorption spectra and atomic force microscopy studies. As a result, a high responsivity about 19.1 A/W at 600 nm and an excellent detectivity more than 1012 Jones ranging from 350 to 600 nm were successfully achieved, which are among the highest values for OPDs and comparable to inorganic counterparts.

Stable, Fast UV-Vis-NIR Photodetector with Excellent Responsivity, Detectivity, and Sensitivity Based on α-In2Te3 Films with a Direct Bandgap.

Photoelectric conversion is of great importance to extensive applications. However, thus far, photodetectors integrated with high responsivity, excellent detectivity, large phototo-dark current ratio, fast response speed, broad spectral range, and good stability are rarely achieved. Herein, we deposited large-scale and high-quality polycrystalline indium sesquitelluride (α-In2Te3) films via pulsed-laser deposition. Then, we demonstrated that the photodetectors made of the prepared α-In2Te3 films possess stable photoswitching behavior from 370 to 1064 nm and short response time better than ca. 15 ms. At a source-drain voltage of 5 V, the device achieves a high responsivity of 44 A/W, along with an outstanding detectivity of 6 × 10(12) cm H(1/2) W(-1) and an excellent sensitivity of 2.5 × 10(5) cm(2)/W. All of these figures-of-merit are the best among those of the reported α-In2Te3 photodetectors. In fact, they are comparable to the state-of-the-art commercial Si and Ge photodetectors. For the first time, we established the theoretical evidence that α-In2Te3 possesses a direct bandgap structure, which reasonably accounts for the superior photodetection performances above. Importantly, the device exhibits a good stability against the multiple photoswitching operation and ambient environment, along with no obvious voltage-scan hysteresis. These excellent figures-of-merit, together with the broad spectral range and good stability, underscore α-In2Te3 as a promising candidate material for next-generation photodetection.

Active Adoption of Void Formation in Metal-Oxide for All Transparent Super-Performing Photodetectors.

Could ‘defect-considered’ void formation in metal-oxide be actively used? Is it possible to realize stable void formation in a metal-oxide layer, beyond unexpected observations, for functional utilization? Herein we demonstrate the effective tailoring of void formation of NiO for ultra-sensitive UV photodetection. NiO was formed onto pre-sputtered ZnO for a large size and spontaneously formed abrupt p-NiO/n-ZnO heterojunction device. To form voids at an interface, rapid thermal process was performed, resulting in highly visible light transparency (85–95%). This heterojunction provides extremely low saturation current (<0.1 nA) with an extraordinary rectifying ratio value of over 3000 and works well without any additional metal electrodes. Under UV illumination, we can observe the fast photoresponse time (10 ms) along with the highest possible responsivity (1.8 A W−1) and excellent detectivity (2 × 1013 Jones) due to the existence of an intrinsic-void layer at the interface. We consider this as the first report on metal-oxide-based void formation (Kirkendall effect) for effective photoelectric device applications. We propose that the active adoption of ‘defect-considered’ Kirkendall-voids will open up a new era for metal-oxide based photoelectric devices.

Ultraviolet photodetector based on MgxZn1-xO films using plasma-enhanced atomic layer deposition

A plasma-enhanced atomic layer deposition (PE-ALD) system was used to deposit magnesium zinc oxide (MgxZn1−xO) films with various Mg content (x). The MgxZn1-xO films were applied to metal–semiconductor–metal ultraviolet (UV) photodetectors (MSM-UPDs) as an active layer. The Mg content in the MgxZn1-xO films was modulated by adjusting the ZnO–MgO cycle ratios to 15:1, 12:1, and 9:1. Correspondingly, the Mg content in the MgxZn1-xO films characterized using an energy dispersive spectrometer was 0.10, 0.13, and 0.16, respectively. The optical bandgap of the MgxZn1-xO films increased from 3.56 to 3.66 eV with an increase in Mg content from 0.10 to 0.16. The peak position of photoresponsivity for the MgxZn1-xO MSM-UPDs was also shifted from 350 to 340 nm. The UV-visible rejection ratios of the MgxZn1-xO MSM-UPDs were higher than 3 orders of magnitude. In addition, excellent detectivity and noise equivalent power for the MgxZn1-xO MSM-UPDs were observed at a bias voltage of 5 V. The high performance of the MgxZn1-xO MSM-UPDs was achieved by PE-ALD at a low temperature.

All Transparent Metal Oxide Ultraviolet Photodetector

A high‐performing UV photodetector that uses large energy bandgap materials of p‐type NiO and n‐type ZnO without an opaque metal electrode is reported. A quality heterojunction is formed by large‐area applicable sputtering deposition method that has an extremely low saturation current density of 0.1 μA cm−2. This abrupt p‐NiO/n‐ZnO heterojunction device is visible‐light transparent and shows the fastest photoresponse time of 24 ms among NiO‐based UV photodetectors, along with the highest responsivity (3.85 A W−1) and excellent detectivity (9.6 × 1013 Jones) properties. Structural, physical, optical, and electrical properties of nanocrystalline NiO are systematically investigated. Mott–Schottky analyses are applied to develop the interface of NiO and ZnO by establishing energy diagrams. Defects existing inside the nanocrystalline NiO film enhance the UV detection performance by defect‐assisted carrier transportation. The results provide a solid scheme of manipulation of NiO defects for functional photoelectric device applications.

Ultraviolet light sensor based on graphene quantum dots/reduced graphene oxide hybrid film

Here, we demonstrate a high performance ultraviolet (UV) light sensor based on graphene quantum dots (GQDs)/reduced graphene oxide (RGO) hybrid film with a simple and inexpensive solution process. To fabricate the GQDs/RGO hybrid film, GQDs synthesized by the carbonization of citric acid are simply sprayed on RGO film prepared by spin-coating on a SiO2/Si substrate. The RGO film is employed as the transport channel of the photogenerated electrons from GQDs due to its superior electron mobility and conductivity. By the integration of GQDs and RGO, the UV sensor device shows a high photo responsibility of 8.7×102A/W and an excellent specific detectivity of 7.7×1013 Jones at a low operating voltage. These results are attributed to the strong absorption of GQDs and the photogenerated charge transfer to RGO. Our novel approach based on the integration of GQDs and RGO can be extended for the design of the other promising optoelectronic applications.

Novel ultra-sensitive detectors in the 10-50 μm wavelength range.

We have developed novel single-photon detectors in the 10–50 μm wavelength region. The detectors are charge-sensitive infrared phototransistors (CSIPs) fabricated in GaAs/AlGaAs double quantum well (QW) structures, in which a photo-generated hole (+e) in the floating gate (upper QW) modulates the conductance of a capacitively-coupled channel located underneath (lower QW). The excellent noise equivalent power (NEP = 8.3 × 10−19 W/Hz1/2) and specific detectivity (D* = 8 × 1014 cm Hz1/2/W) are demonstrated for 15 micron detection up to 23 K, which are by a few orders of magnitude better than those of other state-of-the-art high-sensitivity detectors. The dynamic range exceeds 106 (∼aW to pW) by repeatedly resetting the accumulated holes in the upper QW. Simple device structure makes the detectors feasible for array fabrication: Furthermore, monolithic integration with reading circuits will be possible.