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1.
Nat Commun ; 11(1): 101, 2020 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-31900395

RESUMO

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.

2.
Small ; 16(1): e1904369, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31769618

RESUMO

2D transition metal dichalcogenides (TMDs) based photodetectors have shown great potential for the next generation optoelectronics. However, most of the reported MoS2 photodetectors function under the photogating effect originated from the charge-trap mechanism, which is difficult for quantitative control. Such devices generally suffer from a poor compromise between response speed and responsivity (R) and large dark current. Here, a dual-gated (DG) MoS2 phototransistor operating based on the interface coupling effect (ICE) is demonstrated. By simultaneously applying a negative top-gate voltage (VTG ) and positive back-gate voltage (VBG ) to the MoS2 channel, the photogenerated holes can be effectively trapped in the depleted region under TG. An ultrahigh R of ≈105 A W-1 and detectivity (D*) of ≈1014 Jones are achieved in several devices with different thickness under Pin of 53 µW cm-2 at VTG = -5 V. Moreover, the response time of the DG phototransistor can also be modulated based on the ICE. Based on these systematic measurements of MoS2 DG phototransistors, the results show that the ICE plays an important role in the modulation of photoelectric performances. The results also pave the way for the future optoelectrical application of 2D TMDs materials and prompt for further investigation in the DG structured phototransistors.

3.
ACS Appl Mater Interfaces ; 11(45): 42358-42364, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31633328

RESUMO

Two-dimensional material-based ferroelectric field-effect transistors (2D-FeFETs) hold great promise in information storage and processing. However, an often-observed and hard-to-control anti-hysteresis response of 2D-FeFETs, for example, hysteretic switching of the resistance states of the devices opposite to that of the actual polarization of the ferroelectric dielectric, represents a major issue in the industrial applications of such devices. Here, we demonstrate a van der Waals buffer technique that eliminates anti-hysteresis in black phosphorus (BP) 2D-FeFETs and restores their intrinsic hysteretic behavior. Our modified BP 2D-FeFETs showed outstanding performance including high room-temperature carrier mobility, robust bistable states with fast response to a gate, a large on/off ratio at zero gate voltage, a large and considerably more stable memory window, and a long retention time. During repeated gate operation, the memory window of the buffered device is ∼7000 times more stable than the unbuffered device. Such a method could be crucial in future information technological applications that utilize the intrinsic properties of 2D-FeFETs.

4.
ACS Appl Mater Interfaces ; 11(42): 38895-38901, 2019 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-31556289

RESUMO

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe2-Cr Schottky junction with an asymmetric Schottky contact area of the source and drain. A significant rectification ratio over 105 and multiple rectifying states (e.g., full pass, forward pass, off, and backward pass) were achieved in the single Schottky junction tuned by gate voltage. Furthermore, switching characteristic, rectification characteristic, and amplitude of a sin wave can be effectively modulated by the electrical field or light illumination in a signal process circuit based on the WSe2-Cr Schottky junction. The highly tunable Schottky junction working as a multimode signal processor unit has great potential in future optoelectronic-integrated chips.

5.
Adv Sci (Weinh) ; 6(15): 1901050, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31406679

RESUMO

Broadening the spectral range of photodetectors is an essential topic in photonics. Traditional photodetectors are widely used; however, the realization of ultrabroad spectrum photodetectors remains a challenge. Here, a photodetector constructed by a hybrid quasi-freestanding structure of organic ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with molybdenum disulfide (MoS2) is demonstrated. The 2D MoS2 with the ultrathin structure brings a great benefit of heat dissipation for the pyroelectric infrared detector. By coupling the mechanisms of pyroelectrics, photoconductor, and phototransistor effect, an ultrabroad spectrum response ranging from ultraviolet (375 nm) to long-wavelength infrared (10 µm) is achieved. In the 2.76-10 µm spectral range, the 2D MoS2 is used to read and amplify the photocurrent induced by the pyroelectric effect of P(VDF-TrFE). The sensitivity of the device in this spectral range is greatly enhanced. A high responsivity of 140 mA W-1, an on/off photocurrent switching ratio up to 103, and a quick response of 5.5 ms are achieved. Moreover, the ferroelectric polarization field dramatically enhances the photoconductive properties of MoS2 and restrains dark current and noise. This approach constitutes a reliable route toward realizing high-performance photodetectors with a remarkable ultrabroad spectrum response, high responsivity, low power consumption, and room-temperature operation.

6.
ACS Appl Mater Interfaces ; 11(28): 25108-25114, 2019 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-31268649

RESUMO

The booming frontier of electrochemistry is radically transforming the landscape of global chemical and energy industry. Most recent advancements in electrocatalysts have been built on trial and error, lacking model experiments to illuminate the fundamental factors hidden behind, such as phase, conductivity, and surface coordination environment. Here, we use phase-controllable, highly oriented two-dimensional MoTe2 as the model catalysts. The 2H phase MoTe2's conductivity can be engineered both extrinsically and intrinsically by single-layer graphene and lithiation, bringing down the sheet resistance from 0.95 MΩ/□ to 0.8 kΩ/□ and 0.6 kΩ/□. The corresponding electrocatalytic performance was unlocked from a silent state, catching up to its 1T' counterpart, with a parallel Tafel slope of 141 mV/dec. A focused ion beam further exposed the edge atoms, which exhibited a hydrogen evolution turnover frequency 104 times superior to that of basal plane atoms.

7.
ACS Appl Mater Interfaces ; 11(26): 23667-23672, 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31144499

RESUMO

Recently, two-dimensional (2D) materials, especially transition-metal dichalcogenides (TMDCs), have attracted extensive interest owing to their potential applications in optoelectronics. Here, we demonstrate a hybrid 2D-zero-dimensional (0D) photodetector, which consists of a single-layer or few-layer molybdenum disulfide (MoS2) thin film and a thin layer of core/shell zinc cadmium selenide/zinc sulfide (ZnCdSe/ZnS) colloidal quantum dots (QDs). It is worth mentioning that the photoresponsivity of the hybrid 2D-0D photodetector is 3 orders of magnitude larger than the TMDC photodetector (from 10 to 104 A W-1). The detectivity of the hybrid structure detector is up to 1012 Jones, and the gain is up to 105. Due to an effective energy transfer from the photoexcited QD sensitizing layer to MoS2 films, light absorption is enhanced and more excitons are generated. Thus, this hybrid 2D-0D photodetector takes advantage of high charge mobility in the MoS2 layer and efficient photon absorption/exciton generation in the QDs, which suggests their promising applications in the development of TMDC-based optoelectronic devices.

8.
Small ; 15(17): e1900236, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30932339

RESUMO

Van der Waals epitaxy (vdWE) is crucial for heteroepitaxy of covalence-bonded semiconductors on 2D layered materials because it is not subject to strict substrate requirements and the epitaxial materials can be transferred onto various substrates. However, planar film growth in covalence-bonded semiconductors remains a critical challenge of vdWE because of the extremely low surface energy of 2D materials. In this study, direct growth of wafer-scale single-crystalline cadmium telluride (CdTe) films is achieved on 2D layered transparent mica through molecular beam epitaxy. The vdWE CdTe films exhibit a flat surface resulting from the 2D growth regime, and high crystal quality as evidenced by a low full width at half maximum of 0.05° for 120 nm thick films. A perfect lattice fringe appears at the interfaces, implying a fully relaxed state of the epitaxial CdTe films correlated closely to the unique nature of vdWE. Moreover, the vdWE CdTe photodetectors demonstrate not only ultrasensitive optoelectronic response with optimal responsivity of 834 A W-1 and ultrahigh detectivity of 2.4 × 1014 Jones but also excellent mechanical flexibility and durability, indicating great potential in flexible and wearable devices.

9.
ACS Nano ; 13(3): 3492-3499, 2019 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-30817125

RESUMO

One-dimensional InAs nanowire (NW)-based photodetectors have been widely studied due to their potential application in mid-wavelength infrared (MWIR) photon detection. However, the limited performance and complicated photoresponse mechanism of InAs NW-based photodetectors have held back their true potential for real application. In this study, we developed ferroelectric polymer P(VDF-TrFE)-coated InAs NW-based photodetectors and demonstrated that the electrostatic field caused by polarized ferroelectric materials modifies the surface electron-hole distribution as well as the band structure of InAs NWs, resulting in ultrasensitive photoresponse and a wide photodetection spectral range. Our single InAs NW photodetectors exhibit a high responsivity ( R) of 1.6 × 104 A W-1 as well as a corresponding detectivity ( D*) of 1.4 × 1012 cm·Hz1/2 W-1 at a light wavelength of 3.5 µm without an applied gate voltage, ∼3-4 orders higher than the maximum value of photoresponsivity reported or commercially used MWIR photodetectors. Moreover, our device shows below band gap photoresponse for 4.3 µm MWIR light with R of 9.6 × 102 A W-1 as well as a corresponding D* of ∼8.5 × 1010 cm·Hz1/2 W-1 at 77 K. Our study shows that this approach is promising for fabrication of high-performance NW-based photodetectors for MWIR photon detection.

10.
Adv Mater ; 31(11): e1808035, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30687966

RESUMO

Due to the large gap in timescale between volatile memory and nonvolatile memory technologies, quasi-nonvolatile memory based on 2D materials has become a viable technology for filling the gap. By exploiting the elaborate energy band structure of 2D materials, a quasi-nonvolatile memory with symmetric ultrafast write-1 and erase-0 speeds and long refresh time is reported. Featuring the 2D semifloating gate architecture, an extrinsic p-n junction is used to charge or discharge the floating gate. Owing to the direct injection or recombination of charges from the floating gate electrode, the erasing speed is greatly enhanced to nanosecond timescale. Combined with the ultrafast write-1 speed, symmetric ultrafast operations on the nanosecond timescale are achieved, which are ≈106 times faster than other memories based on 2D materials. In addition, the refresh time after a write-1 operation is 219 times longer than that of dynamic random access memory. This performance suggests that quasi-nonvolatile memory has great potential to decrease power consumption originating from frequent refresh operations, and usher in the next generation of high-speed and low-power memory technology.

11.
ACS Nano ; 12(12): 12416-12423, 2018 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-30408410

RESUMO

The ability to detect linearly polarized light is central to practical applications in polarized optical and optoelectronic fields and has been successfully demonstrated with polarized photodetection of in-plane anisotropic two-dimensional (2D) materials. Here, we report the anisotropic optical characterization of a group IV-V compound-2D germanium arsenic (GeAs) with anisotropic monoclinic structures. High-quality 2D GeAs crystals show the representative angle-resolved Raman property. The in-plane anisotropic optical nature of the GeAs crystal is further investigated by polarization-resolved absorption spectra (400-2000 nm) and polarization-sensitive photodetectors. From the visible to the near-infrared range, 2D GeAs nanoflakes demonstrate the distinct perpendicular optical reversal with a 75-80° angle on both the linear dichroism and polarization-sensitive photodetection. Obvious anisotropic features and the high dichroic ratio of Ipmax /Ipmin ∼ 1.49 at 520 nm and Ipmax /Ipmin ∼ 4.4 at 830 nm are achieved by the polarization-sensitive photodetection. The polarization-dependent photocurrent mapping implied that the polarized photocurrent mainly occurred at the Schottky photodiodes between electrode/GeAs interface. These experimental results are consistent with the theoretical calculation of band structure and band realignment. Besides the excellent polarization-sensitive photoresponse properties, GeAs-based photodetectors also exhibit rapid on/off response. These results demonstrate that the 2D GeAs crystals have promising potential for polarization optical applications.

12.
Nanoscale ; 10(40): 19131-19139, 2018 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-30298891

RESUMO

Limited by the Boltzmann distribution of electrons, the sub-threshold swing (SS) of conventional MOSFETs cannot be less than 60 mV dec-1. This limitation hinders the reduction of power dissipation of the devices. Herein, we present high-performance In2O3 nanowire (NW) negative capacitance field-effect transistors (NC-FETs) by introducing a ferroelectric P(VDF-TrFE) layer in a gate dielectric stack. The fabricated devices exhibit excellent gate modulation with a high saturation current density of 550 µA µm-1 and an outstanding SS value less than 60 mV dec-1 for over 4 decades of channel current. The assembled inverter circuit can demonstrate an impressive voltage gain of 25 and a cut-off frequency of over 10 MHz. By utilizing the self-aligned fabrication scheme, the device can be ultimately scaled down to below 100 nm channel length. The devices with 200 nm channel length exhibit the best performances, in which a high on/off current ratio of >107, a large output current density of 960 µA µm-1 and a small SS value of 42 mV dec-1 are obtained at the same time. All these would not only evidently demonstrate the potency of NW NC-FETs to break through the Boltzmann limit in nanoelectronics, but also open up a new avenue to low-power transistors for portable products.

13.
Small ; 14(48): e1803465, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30328296

RESUMO

Atomic thin transition-metal dichalcogenides (TMDs) are considered as an emerging platform to build next-generation semiconductor devices. However, to date most devices are still based on exfoliated TMD sheets on a micrometer scale. Here, a novel chemical vapor deposition synthesis strategy by introducing multilayer (ML) MoS2 islands to improve device performance is proposed. A four-probe method is applied to confirm that the contact resistance decreases by one order of magnitude, which can be attributed to a conformal contact by the extra amount of exposed edges from the ML-MoS2 islands. Based on such continuous MoS2 films synthesized on a 2 in. insulating substrate, a top-gated field effect transistor (FET) array is fabricated to explore key metrics such as threshold voltage (V T ) and field effect mobility (µFE ) for hundreds of MoS2 FETs. The statistical results exhibit a surprisingly low variability of these parameters. An average effective µFE of 70 cm2 V-1 s-1 and subthreshold swing of about 150 mV dec-1 are extracted from these MoS2 FETs, which are comparable to the best top-gated MoS2 FETs achieved by mechanical exfoliation. The result is a key step toward scaling 2D-TMDs into functional systems and paves the way for the future development of 2D-TMDs integrated circuits.

14.
J Am Chem Soc ; 140(42): 13746-13752, 2018 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-30257558

RESUMO

Graphene-based electric power generation that converts mechanical energy of flow of ionic droplets over the device surface into electricity has emerged as a promising candidate for blue-energy network. Yet the lack of a microscopic understanding of the underlying mechanism has prevented ability to optimize and control the performance of such devices. This requires information on interfacial structure and charging behavior at the molecular level. Here, we use sum-frequency vibrational spectroscopy to study the roles of solvated ions, graphene, surface moiety on substrate and water molecules at the aqueous solution/graphene/polymer interface. We discover that the surface dipole layer of the neutral polymer is responsible for ion attraction toward and adsorption at the graphene surface that leads to electricity generation in graphene. Graphene itself does not attract ions and only acts as a conducting sheet for the induced carrier transport. Replacing the polymer by an organic ferroelectric substrate could allow switching of the electricity generation with long durability. Our microscopic understanding of the electricity generation process paves the way for the rational design of scalable and more efficient droplet-motion-based energy transducer devices.

15.
Adv Sci (Weinh) ; 5(9): 1800237, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30250784

RESUMO

Benefiting from the technique of vertically stacking 2D layered materials (2DLMs), an advanced novel device architecture based on a top-gated MoS2/WSe2 van der Waals (vdWs) heterostructure is designed. By adopting a self-aligned metal screening layer (Pd) to the WSe2 channel, a fixed p-doped state of the WSe2 as well as an independent doping control of the MoS2 channel can be achieved, thus guaranteeing an effective energy-band offset modulation and large through current. In such a device, under specific top-gate voltages, a sharp PN junction forms at the edge of the Pd layer and can be effectively manipulated. By varying top-gate voltages, the device can be operated under both quasi-Esaki diode and unipolar-Zener diode modes with tunable current modulations. A maximum gate-coupling efficiency as high as ≈90% and a subthreshold swing smaller than 60 mV dec-1 can be achieved under the band-to-band tunneling regime. The superiority of the proposed device architecture is also confirmed by comparison with a traditional heterostructure device. This work demonstrates the feasibility of a new device structure based on vdWs heterostructures and its potential in future low-power electronic and optoelectronic device applications.

16.
Nanotechnology ; 29(48): 485204, 2018 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-30215619

RESUMO

Photodetectors with two-dimensional (2D) materials on a SiO2/Si substrate have been extensively explored. However, these photodetectors often suffer from a large gate voltage and relatively low photoresponsivity due to the low efficiency light absorption of 2D materials. Here, we develop a MoS2 photodetector based on the Al2O3/ITO (indium tin oxide)/SiO2/Si substrate with ultrahigh photoresponsivity of 2.7 × 104 A W-1. Most of the incident light is reflected by the interface of stacked Al2O3/ITO/SiO2 substrate, which significantly increases the light absorption of 2D materials. With the help of thinner and high-κ Al2O3 dielectric, the current ON/OFF ratio could exceed 109 with a gate voltage no more than 2 V. Enhanced gate regulation also brings about a relatively high mobility of 84 cm2 V-1 s-1 and subthreshold swing of 104 mV dec-1. Additionally, two different photocurrent generation mechanisms have also been revealed by tuning the gate voltage. The reflection-enhancement substrate assisted MoS2 photodetector provides a new idea for improving the performance of 2D material photodetectors, which can be perfectly combined with other methods.

17.
Small ; 14(22): e1800492, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29717810

RESUMO

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.

18.
Phys Chem Chem Phys ; 20(27): 18200-18206, 2018 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-29796567

RESUMO

In this study, bipolar memristive behaviors were systematically characterized in Ag/Sb2Te3/Ag hetero-junctions. By using in situ Raman and photoluminescence spectroscopy, a direct observation of the bonding environment and band structure confirmed that resistive switches are strongly related to the electronic valence changes in Sb2Te3 and the formation of Schottky barriers at Ag/Sb2Te3 interfaces. Band movement of Sb2Te3 acquired by first-principles calculations also supports the electrostatic barrier charging as a memristive mechanism of Ag/Sb2Te3/Ag heterocells. Independent resistance-switching behaviors that can be utilized in both amorphous and crystalline Sb2Te3 lead to multiple resistance values with a large memory window (104-105) and low read voltage (∼0.2 V), giving rise to a unique multi-level memory concept. This study based on Ag/Sb2Te3/Ag hetero-junctions offers a significant understanding to promote the use of Sb2Te3 and other chalcogenide memristors as promising candidates for compatible high-density memory applications.

19.
Nanotechnology ; 29(24): 244004, 2018 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-29583135

RESUMO

In the past fifty years, complementary metal-oxide-semiconductor integrated circuits have undergone significant development, but Moore's law will soon come to an end. In order to break through the physical limit of Moore's law, 2D materials have been widely used in many electronic devices because of their high mobility and excellent mechanical flexibility. And the emergence of a negative capacitance field-effect transistor (NCFET) could not only break the thermal limit of conventional devices, but reduce the operating voltage and power consumption. This paper demonstrates a 2D NCFET that treats molybdenum disulfide as a channel material and organic P(VDF-TrFE) as a gate dielectric directly. This represents a new attempt to prepare NCFETs and produce flexible electronic devices. It exhibits a 10^6 on-/off-current ratio. And the minimum subthreshold swing (SS) of the 21 mV/decade and average SS of the 44 mV/decade in four orders of magnitude of drain current can also be observed at room temperature of 300 K.

20.
Nanotechnology ; 29(10): 105202, 2018 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-29384728

RESUMO

In recent years, the electrical characteristics of WSe2 field-effect transistors (FETs) have been widely investigated with various dielectrics. Among them, being able to perfectly tune the polarity of WSe2 is meaningful and promising work. In this work, we systematically study the electrical properties of bilayer WSe2 FETs modulated by ferroelectric polymer poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)). Compared to traditional gate dielectric SiO2, the P(VDF-TrFE) can not only tune both electron and hole concentrations to the same high level, but also improve the hole mobility of bilayer WSe2 to 265.96 cm2 V-1 s-1 under SiO2 gating. Its drain current on/off ratio is also improved to 2 × 105 for p-type and 4 × 105 for n-type driven by P(VDF-TrFE). More importantly, the ambipolar behaviors of bilayer WSe2 are effectively achieved and maintained because of the remnant polarization field of P(VDF-TrFE). This work indicates that WSe2 FETs with P(VDF-TrFE) gating have huge potential for complementary logic transistor applications, and paves an effective way to achieve in-plane p-n junctions.

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