Centimeter-Scale Deposition of Mo0.5W0.5Se2 ... - ACS Publications

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Centimeter-Scale Deposition of Mo0.5W0.5Se2 Alloy Film for HighPerformance Photodetectors on Versatile Substrates Zhaoqiang Zheng, Jiandong Yao, and Guowei Yang* State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology Research Center, School of Materials Science & Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong, P. R. China S Supporting Information *

ABSTRACT: Because of their great potential for academic investigation and practical application in next-generation optoelectronic devices, ternary layered semiconductors have attracted considerable attention in recent years. Similar to the applications of traditional layered materials, practical applications of ternary layered semiconductor alloys require the synthesis of large-area samples. Here, we report the preparation of centimeter-scale and high-quality Mo0.5W0.5Se2 alloy films on both a rigid SiO2/Si substrate and a flexible polyimide (PI) substrate. Then, photodetectors based on these alloy films are fabricated, which are capable of conducting broad-band photodetection from ultraviolet to near-infrared region (370−808 nm) with high performance. The photodetector on SiO2/Si substrates demonstrates a high responsivity (R) of 77.1 A/W, an outstanding detectivity (D*) of 1.1 × 1012 Jones, and a fast response time of 8.3 ms. These figures-of-merit are much superior to those of the counterparts of binary material-based devices. Moreover, the photodetector on PI substrates also achieves high performance (R = 63.5 A/W, D* = 3.56 × 1012 Jones). And no apparent degradation in the device properties is observed even after 100 bending cycles. These results make Mo0.5W0.5Se2 alloy a highly qualified candidate for next-generation optoelectronic applications. KEYWORDS: layered materials, Mo0.5W0.5Se2 alloys, pulsed laser deposition, photodetector, broad band

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INTRODUCTION Layered materials, such as MoS2, WS2, MoSe2, and WSe2, have attracted considerable interest in recent years because of their unique layered structures, fascinating electronic and optical properties, and potential applications in next-generation electronic and optoelectronic devices.1−6 The optical and optoelectronic properties of layered materials are strongly dependent on their number of layers.7,8 Typically, layered materials possess sizable band gaps of about 1−2 eV, allowing them to interact with light over a broad bandwidth from ultraviolet (UV) to near infrared (NIR), rendering them as promising material for various photodetectors over a wide spectral range.1 In recent years, photoresponsive devices based on layered materials have received significant attention because of the strong light−matter interactions9 and broad-band light absorption of semiconducting layered materials.10 Applications of these photoresponsive devices include imaging, optical communication, environment monitoring, optoelectronic memory, energy harvesting, security check, night vision surveillance, and so on.11−13 However, typical photoresponsive devices are usually fabricated by binary layered materials.14,15 Because they are synthesized at high temperatures, theoretical investigations indicate that these binary layered materials may suffer from high defect concentrations, especially chalcogen vacancies,16−18 which would lead to the formation of localized deep-level defect © 2017 American Chemical Society

states (DLDSs), which greatly affect the photoresponse performance of the devices.19,20 Alloy engineering is explored to be an alternative solution to suppress DLDSs.17 The isomorphism of the layered material families (MX2: M = Mo, W; X = S, Se, Te) makes them promising candidates to form ternary layered alloys that will not suffer from phase separation.21 Theoretical calculations have indicated that alloys of layered materials, such as ternary Mo0.5W0.5Se222 and Mo0.5W0.5S2,23 are thermodynamically more stable than their binary counterparts, which can be efficient to suppress the formation of binary byproducts during the synthesis process. Moreover, compared to that of the devices based on binary layered materials, experiments have demonstrated that layered material alloys exhibit greater adjusted band alignment in the photoresponsive devices, which is beneficial to enhance the device performance.24,25 Similar to the applications of binary layered materials, practical applications of layered material alloys require the synthesis of large-area samples. Recently, several approaches, such as mechanical exfoliation26 and chemical vapor deposition (CVD),27,28 have been used to achieve layered material alloys. Received: February 14, 2017 Accepted: April 13, 2017 Published: April 13, 2017 14920

DOI: 10.1021/acsami.7b02166 ACS Appl. Mater. Interfaces 2017, 9, 14920−14928

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ACS Applied Materials & Interfaces

Figure 1. Morphology and structure characterizations of the PLD-grown Mo0.5W0.5Se2 alloy film. (a) Digital photograph of the alloy film on Si wafer capped with 300 nm SiO2. (b) SEM image of the as-synthesized Mo0.5W0.5Se2 film. (c) AFM topographic line profile of the alloy film showing thickness of ≈42 nm; inset: AFM image of the scan area. (d) XRD pattern of the Mo0.5W0.5Se2 film; inset: structural model of the layered Mo0.5W0.5Se2 film. EDS mapping images of (e) Mo, (f) W, and (g) Se elements for the same area in (b).

as well as a fast response time of 8.3 ms. We further apply this Mo0.5W0.5Se2 alloy film to wearable flexible photodetectors with superior photodetection performance (R = 63.5 A/W, D* = 3.56 × 1012 Jones). The outstanding figures-of-merit of photodetectors based on Mo0.5W0.5Se2 alloy films on either rigid or flexible substrates provide Mo0.5W0.5Se2 alloys a large scope for practical applications in innovative optoelectronic systems.

Unfortunately, the yield of mechanical exfoliation is relatively low, and the size and shape of the products are uncontrollable;29 furthermore, the CVD process requires high temperatures (>600 °C), which limits the substrates used for the direct growth of layered material alloys.30,31To overcome these challenges, for the broad applications in integrated devices and systems, developing an efficient technology for the direct growth of large-area and high-quality layered material alloys is very important. In this study, we describe the successful preparation of centimeter-scale and high-quality Mo0.5W0.5Se2 alloy films by pulsed laser deposition (PLD). A systematic investigation of ternary Mo0.5W0.5Se2 alloy photodetectors designed on both rigid SiO2/Si and flexible polyimide (PI) substrates has been performed. Impressively, the alloy photodetector on SiO2/Si substrate shows preeminent responsivity of 77.1 A/W at 532 nm. Furthermore, it shows a high detectivity of 1.1 × 1012 Jones

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EXPERIMENTAL SECTION

Preparation of the Mo0.5W0.5Se2 Alloy Film. PLD was exploited to prepare polycrystalline Mo0.5W0.5Se2 alloy films, and the deposition parameters used here are similar to those in our previous works.32−34 First, SiO2/Si substrates were ultrasonically cleaned in acetone, alcohol, and deionized water for 10 min and then dried by N2 flow. Then, they were loaded onto a rotating holder in the deposition chamber located at a distance of 7 cm from the solid target. The target 14921


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Figure 2. Spectroscopic analyses of the layered Mo0.5W0.5Se2 alloy film synthesized by PLD. (a) Raman pattern under a 514 nm excitation laser; inset: zoom-in Raman pattern in the blue box. (b) Fitting results of the Raman pattern. XPS peaks of (c) W, (d) Se, and (e) Mo elements in the Mo0.5W0.5Se2 film. alloy film between the electrodes via PLD. For the flexible device, the Mo0.5W0.5Se2 alloy film was deposited on clean PI substrate. Then, indium tin oxide (ITO) parallel electrodes were deposited on the alloy film similarly to our previous works.31,34 The electrical characterization was performed on a LakeShore probe station connected to a semiconductor characterization system (Keithley 4200) at room temperature. For photodetection, laserdriven light sources with wavelengths ranging from UV to NIR provided the incident light. The illumination with wavelength of 370 nm was generated from the CrystaLaser Class IIIb laser, whereas illuminations with wavelengths of 447, 532, and 808 nm were generated from Viasho lasers. The spot sizes of the lasers were maintained at a diameter of 5 mm, which is much larger than our device. Therefore, in all measurements presented here, our device was fully illuminated.

was composed of highly pure MoSe2 and WSe2 powders (99.99%), whose atomic ratio was 1:1. Then, the deposition chamber was evacuated to a bias pressure of 10−4 Pa, and the substrates were heated to 405 °C. The working pressure was maintained at 20 Pa, and the working gas, highly pure Ar2 (99.99%), was flowing at a rate of 50 sccm. Sequentially, a pulsed laser beam (248 nm) produced by a KrF excimer laser was focused to ablate the target. The operating power of each pulse was constant at 130 mJ, and the total number of pulses was 15 000. The pulse rate was 4 Hz, and the pulse duration was 20 ns. Characterization of the Mo0.5W0.5Se2 Alloy Film. The surface morphologies and compositions of the Mo0.5W0.5Se2 alloy film were acquired by a scanning electron microscope (SEM, FEI Quanta 400F) and an energy-dispersive X-ray spectrometer (EDS, INCA, Oxford Company). The thickness profile was measured on an atomic force microscope (AFM, Bruker Dimension FastScan). The X-ray diffraction (XRD, Rigaku D/MAX 2200 VPC) pattern was recorded with a Cu Kα radiation source (λ = 0.15418 nm). The Raman spectrum of the Mo0.5W0.5Se2 alloy film was collected using a Renishaw InVia spectrometer with an excitation wavelength of 514 nm. The bonding energies of the constituent elements were characterized by highresolution X-ray photoelectron spectroscopy (XPS, Escalab 250, Thermo-VG Scientific) with a monochromatic Al Kα radiation source. The absorption spectrum and the optical transmittance of the alloy film were obtained via a UV−vis−NIR spectrophotometer (LAMBDA 950, PerkinElmer). Device Fabrication and Characterization. For the rigid device, Au−Ti interdigital electrodes were patterned onto the Si/SiO2 substrate by a standard photolithography process, followed by electron-beam evaporation. Subsequently, we covered the electrodes with a stainless steel shadow mask and deposited the Mo0.5W0.5Se2

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RESULTS AND DISCUSSION Morphology and Structure of the Mo0.5W0.5Se2 Alloy Film. Figure 1a presents a typical digital photograph of the PLD-grown Mo0.5W0.5Se2 alloy film on a 1 × 1 cm SiO2/Si substrate. The alloy film uniformly covers the whole area of the substrate, demonstrating that a centimeter-scale Mo0.5W0.5Se2 film is achieved. A high-magnification SEM image is presented in Figure 1b, which clearly reveals the continuous polycrystalline morphology of the alloy film. As can be seen, the film consists of a large number of compact grains, and no pinholes are demonstrated. Furthermore, there are particle-like materials on the alloy film. The distance between two adjacent particles is 14922


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Figure 3. Optoelectronic properties of the Mo0.5W0.5Se2 photodetector. (a) SEM image of a Mo0.5W0.5Se2 photodetector. (b) I−V characteristics of the device in the dark and under light illumination (27 mW/cm2); inset: schematic diagram of the Mo0.5W0.5Se2 photodetector. Mapping of (c) photocurrent and (d) responsivity as a function of power intensity and bias voltage.

In addition, to further assess the crystal structure, the Raman spectrum of the alloy film was recorded under a 514 nm excitation laser, which is shown in Figure 2a. As can be seen, there is a pronounced peak at about 245 cm−1, which can be divided into three peaks, centered at 243.9, 248.1, and 250.7 cm−1. The peaks located at 248.1 and 250.7 cm−1 can be assigned to the WSe2-like E12g and A1g modes, respectively,39 and the peaks at 243.9 and 288.0 cm−1 are originated in the MoSe2-like A1g and E12g modes, respectively.40,41 Additionally, as marked by the labels, we have identified many other weak peaks, which can be assigned to the second-order Raman modes.34 The chemical composition and binding energy of the PLDgrown Mo0.5W0.5Se2 film were examined with XPS. Figure 2c−e presents the binding-energy profiles of W, Se, and Mo, respectively. The peaks observed at the binding energies matched well with the WSe and MoSe bonding characteristics reported by other groups.39,42 The XPS results reveal that Mo, W, and Se elements of the PLD-grown Mo 0.5 W 0.5 Se 2 film exist in a compounded state. The stoichiometric ratio of Mo/W/Se in the film is calculated to be ca. 1:1:4, implying its high crystalline quality.

several nanometers. These particles on the surface may be the precursors of the alloy film. Interestingly, the presence of these nanoparticles can reduce the reflectance of the incident light and improve the light absorption of the alloy film, leading to an improvement in the device performance.35−37 The inset in Figure 1c shows an AFM image at the edge of the alloy film. The root mean square of the alloy film is extracted to be ca. 10.3 nm. To measure the thickness of the Mo0.5W0.5Se2 alloy film, the AFM height profile across the edge of the alloy film is presented in Figure 1c. The thickness is calculated to be about 42 nm. Compared with their monolayer counterpart, such multilayer films could even be better candidates in electronics/ optoelectronics because of their higher optical absorption and longer carrier lifetime.6,38 The XRD pattern of the Mo0.5W0.5Se2 alloy film is presented in Figure 1d, showing only one pronounced peak, which can be indexed as (002). Hence, as schematically depicted in the inset of Figure 1d, the prepared Mo0.5W0.5Se2 film is highly oriented toward c axis. To analyze the detailed chemical composition of the as-synthesized alloy film, the EDS image in Figure S1 manifests the coexistence of Mo, W, and Se elements, whose spatial distributions are depicted in the element mapping images in Figure 1e−g, respectively. Clearly, these elements are distributed uniformly. 14923


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Figure 4. (a) Power-density-dependent photocurrent (Iph, blue) and responsivity (R, red) at a bias voltage of 2 V. (b) Power-density-dependent external quantum efficiency (EQE, blue) and specific detectivity (D*, red) at a bias voltage of 2 V. (c) Time-resolved switching characteristic of the device under a 532 nm illumination at applied biases of 1 V (blue) and 0 V (red). The illumination power density is 27 mW/cm2. (d) Temporal switching curve of a single cycle; time interval is 8.3 ms, and bias voltage (Vds) is 1 V.

and S is the effective area of the photosensitive region.13 As the effective area of our device is 0.425 mm2, Rλ as a function of incident light intensity and Vds is calculated in a twodimensional map, as in Figure 3d. Clearly, the responsivity increases with the increasing of Vds and decreases with increasing of incident light intensity. It is notable that the responsivity of our Mo0.5W0.5Se2 photodetector could reach 77.1 A/W for the 532 nm light irradiation at 25 μW/cm2 under Vds = 2 V. This value is much higher than that of the counterparts of binary MoSe2- and WSe2-based photodetectors.34,41,44,45 To further explore the quantitative dependence of the photocurrent on incident power intensity, as shown in Figure 4a (blue squares), we examined Iph as a function of power intensity at fixed Vds (2 V). Fitting the plot as a power law equation of Iph ∼ Pα, the value of α = 0.4 is achieved. Here, the deviation from the ideal index of α = 1 implies the loss of the photoexcited carriers through recombination. Both defects and charge impurities may be recombination centers, which could be filled by photoexcited charge carriers as the light intensity increases, leading to the Iph saturation. This phenomenon has also been observed in other layered material-based photodetectors.6,15 Meanwhile, Figure 4a (red triangles) shows the plot of Rλ against various illumination intensities. Followed by the power law of Rλ ∼ P−0.61 (red line), Rλ exhibits a significant

Optoelectronic Performance of the Mo0.5W0.5Se2 Photodetector. To explore the optoelectronic properties of the Mo0.5W0.5Se2 alloy film, photodetector using this alloy film was fabricated on asymmetric AuTi electrodes. Concrete details are available in the Experimental Section. Figure 3a shows the SEM image of a Mo0.5W0.5Se2 photodetector, and the schematic diagram of the device is provided in the inset of Figure 3b. From the I−V curves in Figure 3b, we note that the device exhibits an obvious rectifying behavior due to the asymmetric electrode structure.43 From Figure 3b, currents at Vds = −1 and 1 V are 4.3 and 31 μA, respectively, in the dark. Therefore, the rectification ratio is about 7.2. In addition, the source−drain current (Ids) of the device increases significantly when it is illuminated. The corresponding power intensity- and bias voltage (Vds)-dependent photocurrent (defined as Iph = Ilight − Idark) is depicted in Figure 3c. As can be seen, the photocurrent exhibits an increasing tendency with increasing irradiation intensity, which is consistent with the fact that stronger illumination would generate more carriers. Moreover, in Figure 3c, the photocurrent exhibits a positive dependence on the bias voltage. To further determine the photodetection performance, responsivity (Rλ) is an important parameter to judge the sensitivity of a photodetector under light stimulation, which is defined as Rλ = Iph/PS, where P is the light power density defined as light power intensity per illumination area 14924


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Table 1. Summary of Important Figures-of-Merit of Recently Developed Photodetectors Based on Layered Materialsa

a

device

method

responsivity (A/W)

EQE (%)

detectivity (Jones)

response time (ms)

ref

ML Mo0.5W0.5Se2 (rigid) ML Mo0.5W0.5Se2 (flexible) 1L MoSe2 FL MoSe2 FL WSe2 FL WSe2 ML WSe2 1L MoS2 ML WS2 FL GaTe FL Bi2S3 FL In2Se3 FL SnS2 BL SnSe2 FL MoTe2 FLMoTe2

PLD PLD CVD exfoliation CVD exfoliation PLD exfoliation PLD exfoliation solvothermal exfoliation CVD CVD exfoliation exfoliation

77.1 63.5 0.013 97.1 3.717 0.1 0.92 0.007 0.51 800 4.4 98 000 260 1100 6 0.11

18 019 14 832 ND 22 666 860 40 180 ND 137 ND 860 ND 93 000 260 000 ND 12.9

1.13 × 1012 3.56 × 1012 ND ND ND ND ND 1.3 × 109 2.7 × 109 2.4 × 1013 1011 3 × 1013 1010 1010 ND ND

8.3 ND 60 15 ND 10−2 0.9 50 4100 300 10 9000 20 14.5 0.16 0.024

this study this study 41 57 44 45 34 52 29 53 51 54 15 6 58 59

ND: No data. 1L, FL, and ML indicate monolayer, few-layer, and multilayer, respectively.

Figure 5. Transparent and flexible photodetector based on the Mo0.5W0.5Se2 alloy film. (a) Transmittance of the assembled photodetector on transparent PI substrates. Inset: photograph of the transparent Mo0.5W0.5Se2 photodetector on a flower image; the device area is shown by the dotted red square. (b) I−V characteristics of the flexible device acquired in the dark and under light illumination. Inset: photograph of the flexible Mo0.5W0.5Se2 photodetector in a flexed state. (c) The calculated responsivity (blue) and specific detectivity (red) as a function of the power density acquired before and after bending 100 times at Vds = 2 V. (d) Typical time-resolved response curves of the device before and after bending 100 times.

between the Mo0.5W0.5Se2 film and the underlying SiO2 substrate.46,47

decrease with increasing illumination power. The decrease in Rλ may be attributed to the large quantity of traps at the interface 14925


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lengths. All of them decrease as the power density increases. At low irradiation intensity, this device achieves high performance in all wavelengths, confirming its broad-band photodetection capability. Flexibility and Compatibility of the Mo0.5W0.5Se2 Photodetector. Finally, because of their high conductivity and mechanical strength, layered materials are particularly valuable for wearable devices.34 In this regard, we further design a flexible and transparent Mo0.5W0.5Se2 photodetector on PI substrate. As depicted in Figure 5a, the photodetector shows a high transparency, average 65%, across the visible region from 400 to 800 nm. Its transparency is further demonstrated by the visibility of the flower beneath the transparent photodetector (inset in Figure 5a). A typical photograph of the flexible Mo0.5W0.5Se2 photodetector in a flexed state is illustrated in the inset of Figure 5b, demonstrating the device’s mechanical flexibility. The I−V curves of the flexible photodetector before and after bending 100 times are presented in Figure 5b. Clearly, unlike the device fabricated on a rigid SiO2/Si substrate, this flexible photodetector holds an ohmic contact between the Mo0.5W0.5Se2 channel and the ITO electrodes. Moreover, the current acquired in the dark and under light illumination changes a little even after bending 100 times, indicating a good mechanical flexibility. On light illumination, our device becomes conductive because of the presence of photoexcited carriers in the Mo0.5W0.5Se2 channel. The light powerdependent responsivity and detectivity recorded before and after bending 100 times are shown in Figure 5c. We observed that the performances are reduced slightly after bending, for example, the responsivity decreases from 63.5 to 60.2 A/W and the detectivity reduces from 3.56 × 1012 to 3.37 × 1012 Jones. The decrease in responsivity and detectivity after bending is likely due to the formation of cracks in ITO electrodes, which reduces the collection efficiency of photoinduced carriers. Similar phenomena have also been observed in other flexible photodetectors.15,48,55 Actually, the values of these parameters are higher than those of other reported flexible photodetectors based on layered materials.15,48,56 Moreover, as illustrated in Figure 5d, the flexible photodetector also shows a highly stable photoresponse before and after bending the device 100 times. Nevertheless, the stretchable nature of this Mo0.5W0.5Se2 alloy film in flexible device is suitable for advanced optoelectronic applications.

Next, we determined other two important parameters in photodetection, EQE and D*, for the Mo0.5W0.5Se2 alloy photodetector. EQE reflects the ratio of electrons flowing out of the device in response to impinging photons and is expressed as EQE = hcRλ/λe, where h is Planck’s constant, c is the speed of light, λ is the wavelength of excitation light, and e is the elementary electronic charge.48 The blue squares in Figure 4b present the power-dependent EQE of the photodetector based on the relationship between EQE and Rλ; the figure shows a maximum EQE of 18019%. Furthermore, the sensitivity of the Mo0.5W0.5Se2 photodetector is quantified by the measurement of D*. Considering the shot noise from the dark current (Idark) dominates the total noise in our case, D* can be defined as D* = RλS1/2/(2eIdark)1/2. The red triangles in Figure 4b present the D* of our Mo0.5W0.5Se2 photodetector measured with respect to the power of incident light. The value of D* decreases with the power of incident light in both log scale and linear scale, and reaches a maximum value of 1.1 × 1012 Jones. This high D* is superior to that of many other reported layered materialbased photodetectors, such as SnSe2 (1.01 × 1010 Jones)6 and SnS2 (1.9 × 109 Jones).15 In fact, such D* value is also close to that of the advanced commercial Si (3 × 1012 Jones) and Ge (3 × 1011 Jones) photodetectors.49 Then, in Figure 4c, the cycling behavior of the photodetector was also checked with a succession of on/off illumination at Vds = 0 V (red) and 1 V (blue). The Mo0.5W0.5Se2 device exhibits definite switching characteristics and maintains good reproducibility for multiple cycles. Although the dark current, photocurrent, and noise performances are almost at the same level, suggesting the great photodetection stability and fast response time, the latter exceeds the measuring limit of the present setup (0.2 s). To estimate the response rate of our device, we maintain the bias voltage (Vds) at 1 V, and the enhancement of the single response and the reset cycle is recorded in Figure 4d. Defining the response time as the photocurrent increases from 0 to 80% of the stable state, we find a fast response time constant of ∼8.3 ms. Such fast response time can be attributed to the high quality and layered crystallographic structure of the Mo0.5W0.5Se2 alloy film. Moreover, taking advantage of the asymmetric electrode structure, both photoinduced electrons and holes can drift freely toward the electrodes in the forward bias direction. The carrier recombination will be suppressed effectively because the electron−hole pairs can be separated and transported readily. Therefore, the use of asymmetric Au Ti electrodes can give rise to much enhanced device response speed.50 For a clear comparison, Table 1 summarizes the relevant figures-of-merit of recently developed photodetectors based on various emerging layered materials. In general, our data were among the top level, considering the overall performances, which reveals the superiority of the Mo0.5W0.5Se2 alloy in photodetection applications.51−54 Then, broad-band photoresponse of the constructed photodetectors is also investigated. Figure S2 presents the optical absorption spectrum of the Mo0.5W0.5Se2 alloy film. As can be seen in the figure, the alloy film exhibits a broad-band absorbance range covering from UV to NIR, revealing the feasibility of broad-band photodetection. Figure S3a shows power-dependent photocurrents under illumination with various wavelengths. These photocurrents also exhibit positive dependence on the incident light intensity, providing good tunability for multifunctional applications. Figure S3b−d presents the corresponding power-dependent responsivity, EQE, and detectivity under illumination with various wave-

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CONCLUSIONS In summary, centimeter-scale and high-quality Mo0.5W0.5Se2 alloy films were prepared on both a rigid SiO2/Si substrate and a flexible PI substrate by PLD. Photodetectors based on these alloy films have been fabricated, and their optoelectronic properties were investigated systematically. Photodetectors on the SiO2/Si substrate were investigated to provide a high Rλ of 77.1 A/W, outstanding D* of 1.1 × 1012 Jones, and a fast response time of 8.3 ms. These figures-of-merit are much superior to those of other recently developed layered materialbased photodetectors. Moreover, the flexible photodetector of the Mo0.5W0.5Se2 alloy film manufactured on the PI substrate also exhibits comparable device performance to those fabricated on the rigid SiO2/Si substrate. With such excellent optoelectronic merits, we envision that the Mo0.5W0.5Se2 alloy film will become a promising candidate to construct a novel optoelectronic system. 14926


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b02166. EDS image of the alloy film, optical absorption spectrum of the alloy film, broad-band photodetection of the alloy photodetector (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Guowei Yang: 0000-0003-2141-6630 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the National Natural Science Foundation of China (50902097) and State Key Laboratory of Optoelectronic Materials and Technologies.

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REFERENCES

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