Article Cite This: ACS Photonics 2017, 4, 2930-2936
pubs.acs.org/journal/apchd5
Surface Oxidation Doping to Enhance Photogenerated Carrier Separation Efficiency for Ultrahigh Gain Indium Selenide Photodetector Yih-Ren Chang,† Po-Hsun Ho,‡ Cheng-Yen Wen,† Tzu-Pei Chen,† Shao-Sian Li,† Jhe-Yi Wang,† Min-Ken Li,† Che-An Tsai,§ Raman Sankar,∥,⊥ Wei-Hua Wang,§ Po-Wen Chiu,‡ Fang-Cheng Chou,∥,# and Chun-Wei Chen*,†,# †
Department of Materials Science and Engineering, National Taiwan University, Taipei, 10617, Taiwan Department of Electrical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan § Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan ∥ Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan ⊥ Institute of Physics, Academia Sinica, Taipei, 11529, Taiwan # Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Kaohsiung 80424, Taiwan ‡
S Supporting Information *
ABSTRACT: This work presents an ultrahigh gain InSebased photodetector by using a novel approach called the surface oxidation doping (SOD) technique. The carrier concentration of multilayered two-dimensional (2D) InSe semiconductor surface has been modulated by controlling the formation of a surface oxide layer. The SOD through surface charge transfer at the interface of the oxide/2D InSe semiconductor heterostructure can lead to the creation of a vertical built-in potential and band bending as a result of the carrier concentration distribution gradient. The internal electric field caused by the formation of a carrier concentration gradient in InSe layers can facilitate charge separation of photogenerated electron−hole pairs under light illumination. Consequently, the record high photoresponsivities of InSe-based photodetector with ∼5 × 106 A/W at the excitation wavelength of 365 nm and 5 × 105 A/W at the wavelength of 530 nm can be obtained, outperforming the majority of photodetectors based on other 2D materials, such as graphene, MoS2, and even highly sensitive multilayer GaTe and In2Se3 flakes. The approach based on SOD induced efficient photogenerated charge separation can be also applied to other 2D layered semiconductors. KEYWORDS: indium selenide, field effect transistor, surface oxidation, p-doping, photodetector
I
conductor transport behavior with remarkably high mobilities at room-temperature (up to ∼2000 cm2 V−1 s−1 based on the four probe measurement and ∼300 cm2 V−1 s−1 based on the two probe measurement),10 making it promising for semiconductor electronic or optoelectronic applications. However, unlike TMDs, InSe is very sensitive to moisture and oxidation occurs spontaneously as exposed to the air, resulting in the oxidation of In2+ into the relatively stable In3+ due to the lower free energy of the chemical compound composed of In3+.11 Accordingly, a surface oxidation layer can easily form on the surface of InSe as exposed to the ambient air.12 Such uncontrolled oxidation at ambient air may usually result in a considerable current hysteresis and cause serious degradation of
n the past decade, two-dimensional (2D) layered materials have attracted great attention after the successful exfoliation of graphene, which exhibits superior carrier transport because of its unique two-dimensional energy dispersion.1 However, the absence of an intrinsic band gap of graphene largely limits its application in semiconductor logic devices.2 Recently, the 2Dlayered semiconductor materials of transition-metal dichalcogenides (TMDs) with inherent band gaps, such as MoS2 and WS2 have demonstrated great potential as the building blocks for next-generation logic circuits by enabling ultrathin highquality semiconducting channels.3,4 Another emergent 2D semiconductor family formed by III−VI group elements (GaSe, In2Se3, InSe, etc.) have also attracted great attention because of their outstanding device performances in photodetection.5−7 In particular, indium selenide (InSe), which possesses a low effective electron mass of 0.156 m08 and a moderate band gap of 1.26 eV9 exhibited excellent semi© 2017 American Chemical Society
Received: September 10, 2017 Published: October 24, 2017 2930
DOI: 10.1021/acsphotonics.7b01030 ACS Photonics 2017, 4, 2930−2936
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Figure 1. (a) AFM image of oxygen plasma treated InSe flake and height profiles variation after oxygen plasma treatment. The black line and red line of AFM line profiles stand for the flake thickness before and after 20W oxygen plasma treatment for 5 s, respectively. (b) Cross-sectional STEM image of oxygen plasma oxidized InSe. (c) Optical image (inset) and gate-dependent conductivity of the InSe FET before and after oxygen plasma treatment. The scale bar in the inset image is 10 μm. (d) Schematic representation of indirect incident plasma treatment on InSe FET.
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the device performance.13 It is well-known that the growth of a high-quality oxide film on a semiconductor with a controllable manner is the most critical issue for the development of advanced electronic and optoelectronic devices as for silicon.14 Recently, atomically flat oxide films formed on the surface of 2D-TMD (WSe2) based on the layer-by-layer self-limitation oxidation technique have been reported, where controllable and uniform surface oxidation on the 2D semiconductor/oxide heterostructures can be achieved.15 In this work, we would like to demonstrate a novel approach to modulate the carrier concentration of multilayered InSe semiconductor by controlling the formation of a surface oxide layer. The surface oxidation doping (SOD) through surface charge transfer near the interface of oxide/2D InSe semiconductor heterostructures may lead to the creation of a vertical built-in potential and band bending as a result of the carrier concentration distribution gradient. The internal electric field caused by the formation of a carrier concentration gradient in InSe layers can facilitate charge separation of photogenerated electron−hole pairs under light illumination. Enhanced photogenerated charge separation efficiency by the SOD effect results in the remarkably enhanced photoresponsivities of InSe-based photodetectors with ∼5 × 106 A/W at the excitation wavelength of 365 nm and 5 × 105 A/W at the wavelength of 530 nm, outperforming the majority of photodetectors based on other 2D materials, such as graphene, MoS2, and even highly sensitive multilayer GaTe and In2Se3 flakes.6,16−18
RESULTS AND DISCUSSION Besides the impressed intrinsic electrical transport properties, as mentioned above, InSe also possesses the unique nature of thickness-dependent bandgaps and optical properties.9 A directto-indirect bandgap transition can be observed as the InSe flake thickness is shrinking to only few nanometers,19 in contrast with the indirect-to-direct band gap transition in 2D-TMDs.20 The bandgap energies of InSe vary from 1.26 eV of a bulk crystal to near 3 eV of a monolayer.10 The moderate bandgap energies together with the direct bandgap characteristics could make the multilayer InSe as a potential candidate for optoelectronic applications. Because of the intrinsically unstable nature of the few layer InSe flake, the surface of the asexfoliated InSe flake becomes rapidly oxidized in ambient air. Here, the multilayer InSe flake was initially exfoliated from the bulk crystal by the conventional Scotch tape method and transferred to the silica substrate with a 285 nm silicon oxide layer in a glovebox under inert atmosphere. Hence, the device fabrication during exfoliation and transfer processes performed in the glovebox can effectively retard the chemical reaction with water or oxygen. Subsequently, we carried out the oxidation process for the top surface of multilayered InSe. When the asexfoliated multilayered InSe was exposed to the ambient atmosphere, spontaneous oxidation occurred. The oxide layer formed under ambient atmosphere exhibited a rugged surface with numbers of spotty bumps ranging from 100−300 nm in width and 3−20 nm in height, showing a root-mean-square roughness up to 1.17 nm. (Supporting Information, Figures S1b and S2). The spontaneous oxidation can go deep into the 2931
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thick. The SOD effect becomes more prominent when the duration time of the plasma treatment was increased (not shown here). However, such rapid oxidation by direct plasma treatment on InSe is still difficult to provide a controllable doping with gradually increased hole concentrations on the multilayered InSe flake. Here, we introduce an alternative oxygen plasma oxidation process as shown schematically in Figure 1d, where indirect incident plasma oxidation was applied instead to provide a milder and more controllable surface oxidation doping on InSe. In brief, the samples were placed near the chamber wall with at an incident angle of 45° to the plasma source to avoid the strong collision of directional O2 plasma. Less-directional activated plasma would reach the samples and result in a mild oxidation in contrast to the directional plasma treatment under the normal incident. The details of the indirect incident plasma oxidation treatment will be provided in the Supporting Information. Through the indirect plasma treatment, it is possible to modulate the degree of surface oxidation on multilayered InSe flake, obtaining a controllable SOD with adjustable doping concentrations compared to that using the normal incident oxygen plasma treatment. Further, the as-exfoliated InSe sample under the indirect incident oxygen plasma treatment with incremental duration time was performed. Figure 2(a) shows the evolution of gatedependent current characteristic curves of the 17 nm-thick multilayered InSe flake as a function of the duration time by the indirect oxygen plasma (IP) treatment. Before the oxygen plasma treatment, the intrinsic transport behavior of the asexfoliated pristine InSe FET (black curve) exhibited a typical n-
inner layers because of the loose structure of the resulting oxides. In order to obtain a more homogeneous and uniform surface oxidation layer, as-exfoliated InSe thin films were treated with a low power (20W) oxygen plasma in a plasma cleaner chamber immediately followed by the exfoliation process. The upper part of Figure 1a shows the AFM image of the few-layered InSe flake under the plasma treatment for 5 s. It is found that the surface oxidation layer created by the oxygen plasma treatment shows a smooth and uniform surface morphology with a root-mean-square roughness about 0.29 nm, similar to that on the pristine InSe surface before plasma treatment (as shown in the AFM image of Figure S1a,c). The bottom part of Figure 1a exhibited the height profiles of the multilayered InSe before and after oxygen plasma treatment, where the thickness of the InSe flake was uniformly increased around 0.55 nm after the plasma treatment, in contrast to the rough bumpy surface oxide layer of InSe exposed to ambient air. In addition, it is well-known that growth of the surface oxidation layer could be both down into the InSe layers and up out of it.21 To obtain a further insight into the formation of the surface oxidation layer, Figure 1b shows the cross-sectional high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the multilayer InSe flake under plasma treatment. A ∼2 nm thick noncrystalline layer was found to form homogeneously on top of the crystalline InSe flake, which represents the thin and dense amorphous layer due to oxygen plasma treatment compared to the bumpy surface formed when it was exposed to the ambient air. Although the oxidation reaction only took place near the top few InSe layers with the 5 s plasma treatment, the electronic transport behavior of the multilayer InSe flake was influenced dramatically by the formation of the ultrathin surface oxidation layer. Figure 1c exhibits the current voltage characteristic curves of a field effect transistor (FET) device before and after plasma treatment. As the pristine multilayer InSe FET device shows a typical n-type transporting behavior, a large positive threshold voltage shift ΔVth (∼36 V) is found, indicating that the strong hole doping effect occurs after the formation of the ultrathin surface oxidation layer by oxygen plasma treatment. The corresponding hole doping concentrations can be obtained according to the eq 122
nh =
C i(ΔVth) q
(1)
where ΔVth is the shift of threshold voltage, Ci is the capacitance per unit area of the dielectric given by Ci = ε0εr/ d, with εr and d are the dielectric constant and the thickness of SiO2, respectively. The hole doping density created by oxygen plasma oxidation on the FET device was estimated to be 2.7 × 1012 cm−2. Meanwhile, the mobility of the FET also drops significantly to less than 50% because of the strong hole doping effect. The origin of such strong SOD is mainly due to the electron charge transfer from underneath InSe to the top capping oxidation layer, similar to the previous report in WOxcovered WSe2.23 The formation of an atomically thin oxide layer on the surface of the WSe2 flake typically required the exposure to O3 under 100 °C for 1 h.15 However, the oxidation process on InSe progressed much faster compared to that on WSe2 because of the high oxidation activity in InSe. Accordingly, the strong SOD effect on the multilayer InSe device with a largely increased hole doping concentration is observed even though the thin oxidation layer is only ∼2 nm-
Figure 2. (a) Evolution of conductivity versus gate-voltage curves for the InSe FET with increased oxidation duration under indirect incident plasma (IP). The inset shows the logarithm scale I−Vg curve with the increased oxidation degree. (b) Evolution of InSe FET mobility and hole doping density with increased oxidation degree. 2932
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Figure 3. XPS spectra of (a) O 1s core level and (b) In 3d core level in different oxidation degree. (c) PL spectra of InSe flakes with different oxidation degree. (d) TRPL spectra of InSe flakes with different oxidation degree measured in 65 K. (e, f) Schematic representation of hole doping gradient and the charge separation enhancement mechanism, respectively.
concentrations as a function of different degrees of surface oxidation. The result indicated that the hole doping concentrations due to surface oxidation doping (SOD) on the InSe FET device can be controlled and modulated through the indirect incident oxygen plasma treatment. As the duration of surface oxidation treatment is increased, the hole doping concentrations in the InSe FET device are also gradually increased, together with the suppression of the electron mobilities. We further employed the XPS measurement to analyze the chemical compositions of the surface oxidation layers formed on top of InSe. Here, three samples are chosen to represent the InSe samples under different degrees of surface oxidation, which are the pristine (without oxidation treatment), mild oxidation (oxidized with indirect incident plasma for 10 s) and strong oxidation (oxidized with indirect incident plasma for 60 s) samples, respectively. Figure 3a shows the O 1s XPS spectra of three samples. A small but discernible peak located at 532.5 eV was found in the pristine InSe sample, which is mainly attributed to unavoidable rapid oxidation of InSe in the process of loading the sample to the XPS chamber. For the InSe samples under oxygen plasma treatment (mild oxidation and strong oxidation), the intense and prominent O 1s peaks are
type transport characteristic curve with a high mobility of 412 cm2 V−1 s−1 and the current on/off ratio exceed 107 as shown in the Supporting Information. The outstanding device performance with a high mobility and a large on/off ratio of the pristine InSe transistor is mainly attributed to our modified sample preparation processes. Because the entire exfoliation and transfer processes were conducted in a glovebox filled with inert N2 gas, the bottom surface of the InSe flake could avoid the possible oxidation before being transferred to the silica substrate compared to the conventional transfer method at ambient condition. It is especially important for a highperformance 2D FET device based on back-gate control to retain a high quality bottom surface.24 After the indirect plasma treatment on the as-exfoliated multilayered InSe flake, it was found that n-type electron transport behavior of the InSe FET device was gradually suppressed, accompanying with the increasing threshold voltage shift values ΔVth as shown in the current−voltage curves of Figure 2a with logarithmic scale inset plot. This is mainly attributed to increased hole concentrations as a result of surface oxidation doping. The corresponding hole doping concentrations at different degrees of surface oxidation can be further estimated according to eq 1. Figure 2b shows the dependence of the electron mobilities and hole doping 2933
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Figure 4. (a) Photocurrent of InSe FET measured as a function of time at the photovoltaic mode under different oxidation degree. (b) Photoresponse cycles of the InSe FET by SOD (strongly oxidized) under light illumination. The inset shows the response curve under the single illumination cycle.
increased surface oxidation, giving a τpristine = 23.8 ns, τmild = 13.6 ns, and τstrong = 4.12 ns. The decreased PL emission yields and the shorten PL lifetime indicated that the formation of an ultrathin surface oxidation layer on top of InSe may lead to efficient separation of photogenerated electron−hole pairs under light illumination owing to the SOD effect. Because the surface oxidation layer is formed only on the top few layers of InSe by the plasma treatment according to the above result, the increased hole doping concentration at the oxide/InSe interface through the SOD effect is expected to much larger compared to that away from the oxide/InSe interface. Accordingly, the carrier concentration distribution gradient induced by SOD may result in the formation of the vertical built-in potential and band bending induced in InSe layers. The internal electric field caused by the formation of a carrier concentration gradient may thus result in the efficient photogenerated carrier separation under light illumination as shown schematically in Figure 3e,f. This may explain the observation of the decreased PL emission yield and the shortened PL lifetime as a result of the formation of an ultrathin surface oxidation layer on top of InSe by the SOD effect. The proposed model of SOD induced efficient photogenerated charge separation in InSe layers can be further evident from the photoresponse of the InSe FET device when it was under illumination without applying an external bias. The photoresponse of the device under the operation condition at the photovoltaic mode without applying an external bias is mainly attributed to the built-in electric field to separate the photogenerated electron−hole pairs, which may propel electrons and holes toward opposite directions, as shown in Figure 3f. Figure 4a shows the photoresponse curves of the InSe FET devices operated at the photovoltaic mode for the asexfoliated, mildly oxidized, and strongly oxidized samples. Because of the SOD effect, the strongly oxidized device consisting of a highest hole doping concentration exhibits a largest photocurrent under light illumination. In contrast, a nearly negligible photocurrent was observed at the as-exfoliated InSe sample under the same operation condition. The result suggests that the SOD effect on InSe may facilitate the separation of photogenerated electron−hole pairs for the InSe FET device operated at the photovoltaic mode as a result of the built-in internal electric field, consistent with the above data of PL intensity quenching and PL lifetime shortening. Figure 4b shows the corresponding photoresponse cycles of the InSe FET by SOD (strongly oxidized) under light illumination which
attributed to the formation of the surface oxidation layers. Figure 3b shows the In 3d core level spectra of the three different samples. The formation of peaks at 445.3 and 452.8 eV correspond respectively to 3d 5/2 and 3d 3/2 lines of indium in the as-exfoliated InSe sample without oxidation treatment. The corresponding binding energies downshift as the InSe samples were treated by oxygen plasma, representing typical hole doping characteristics because of the reduction in the electron densities, which may result in the decreased binding energies. Because of the SOD effect with electron transfer from the pristine InSe inner layers to the surface oxide layer, the binding energies in In 3d peaks were gradually reduced with increased surface oxidation. The enhanced hole doping characteristics of the multilayered InSe flakes caused by SOD at the In 3d core level XPS spectra are consistent with the above transport behaviors of devices of the three different samples. Beside the downshift in binding energies, a pair of weaker doublet peaks (marked in green color) with higher binding energies after the oxidation treatment were also observed and deconvoluted, corresponding to the 3d5/2 and 3d3/2 lines of In3+ existing in the surface oxidation layers. The compositions of the oxidation layers could be conjectured to be either stoichiometric or nonstoichiometric indium oxide (InOx with x ≤ 1.5) accompanying with In2Se3 from the ternary phase diagram11 along with the reaction pathways of the InSe oxidation process25 as described in following: 3 1 O2 → In2O3 + Se 4 2 1 1 1 InSe + O2 → In2Se3 + In2O3 4 3 6 3 In2Se3 + O2 → In2O3 + 3Se 2 InSe +
(2)
Figure 3c,d show the photoluminescence (PL) emission spectra and time-resolved photoluminescence (TRPL) spectra of InSe before and after plasma treatment. Three samples with different degrees of oxidation were measured, corresponding to the as-exfoliated, mild-oxidized and strong oxidized multilayer InSe flakes, similar to the samples at the above XPS analyses. The original as-exfoliated InSe sample exhibited a PL emission spectrum centered at 970 nm corresponding to a band gap of about 1.28 eV. The PL emission yield of InSe was found to be significantly quenched under the treatment of surface oxidation. The corresponding TRPL decay curves of the three samples show a monotonic decrease at the measured lifetime with the 2934
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Figure 5. (a) Photocurrent of InSe FET measured as a function of time with Vd = 2 V and Vg = 60 V under different oxidation degree. (b) Evolution in photoresponsivity of the InSe phototranistor with different oxidation degree and different illumination wavelengths. (c) Photoresponsivities of InSe FET treated with indirect incident plasma treatment for 10 s at different illumination wavelengths.
of the assistance of SOD enhanced charge separation, both the minimum detectable illumination power and the photo responsivity of the device were significantly improved compared with those of the pristine InSe sample (Figure S6 (d)). Ultrahigh photo responsivities of ∼5 × 106 A/W with the illumination wavelength at 365 nm and ∼5 × 105 A/W at the wavelength of 530 nm could be obtained. To the best of our knowledge, these are the highest responsivity values reported in InSe phototransistors up to now. In order to further extend the applicability of this technique, the similar oxidation processes were also conducted on another 2D semiconductor, indium(III) selenide (In 2 Se 3 ), as shown in the Supporting Information. Similar observation with an increased responsivity of the multilayered In2Se3 flake by SOD can be also obtained, indicating that SOD induced efficient photogenerated charge separation can be applied to other 2D layered semiconductors.
exhibited a fast response speed with a response time shorter than 50 ms. By contrast, another operation condition for a photodetector is the photoconductive mode, where the photoexcited electron−hole pairs are separated by the external applied bias VDS and the free electrons and holes drift oppositely toward the source/drain electrodes.7 Photocurrent from the photoconductive effect, IPC, would arise from an increase in photogenerated excess carriers concentration as IPC = qμnEWD (eq 2),6 where μ is the carrier mobility, n is the excess carrier density, E is the electric field in the channel, W is the channel width, and D is the absorption depth. A photoconductor usually has a gain much larger than unity because of the longer photoinduced minor carrier lifetime at the expense of response speed.26,27 Figure 5a shows the photoresponse curves of the InSe FET devices operated at the photoconductive mode before and after surface oxidation treatment. Due to the enhanced separation efficiency of photogenerated electron−hole pairs by the SOD effect, increased photocurrent of the InSe FET device after surface oxidation treatment can be clearly observed. Attributed to two unique advantages of an intrinsic high electron mobility of InSe and an enhanced charge separation efficiency by the SOD effect, the photoresponse with an ultrahigh gain based on the InSe FET device can be obtained. Figure 5b exhibits the broadband spectral response (365−850 nm) of InSe-based photodetectors as a function of various oxidation conditions. It is found that the responsivities of the InSe-based photodetectors are increased with enhanced SOD until the hole doping concentration reaches to a value of 7 × 1011 cm−2, corresponding to the InSe sample under the indirect incident plasma treatment for 10s. Further increase in the hole doping concentration may result in the decline of the responsivities of the devices. Typically, the photodetector operated at the photoconductor mode strongly depends on the product of photogenerated excess carrier concentrations and carrier mobilities according to eq 2. When the hole doping concentrations in the InSe FET devices are increased owing to the SOD effect, the suppression of the electron transport mobilities of the devices may also occur as shown in Figure 2b. Therefore, the device exhibited the best-performed responsivities in photodetection at the optimal hole concentration and mobility, corresponding to the oxidation condition under indirect incident plasma treatment for 10 s. Figure 5c displays the power-dependent responsivities of the best-performed device prepared under the optimal SOD condition. Because
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CONCLUSION
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ASSOCIATED CONTENT
In summary, we have demonstrated a novel approach by controlling the formation of the surface oxide layer to obtain ultrahigh gain InSe-based photodetectors. Through the creation of a vertical built-in potential in 2D multilayered InSe semiconductor by surface oxidation doping (SOD), the efficiency of charge separation of photogenerated electron− hole pairs is largely increased. This unique technique called as the controllable surface oxidation doping (SOD) is found to be effective to modulate the carrier concentrations, which in turn provides a potential path to enhance the photodetection performance of InSe and other 2D layered semiconductors.
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsphotonics.7b01030. Comparisons between ambient air oxidation and plasma oxidation, cross-sectional coposition analysis of oxygen plasma oxidized InSe, details of plasma oxidation processes, fabrication, and measurement of InSe devices, and oxidation effect on layered metal chalcogenides beyond InSe and comparison with other 2D-based photodetectors (PDF). 2935
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Po-Hsun Ho: 0000-0001-8319-0556 Cheng-Yen Wen: 0000-0002-9788-4329 Shao-Sian Li: 0000-0003-4236-1851 Raman Sankar: 0000-0003-4702-2517 Po-Wen Chiu: 0000-0003-4909-0310 Chun-Wei Chen: 0000-0003-3096-249X Author Contributions
Y.-R. designed and took most of the experimental measurements. P.-H. helped the experiment design. P.-H. and P.-W. helped the Raman and PL measurement. C.-Y. helped the STEM and EDS analysis and the revision of manuscript. T.-P. helped the TRPL measurement. J.-Y. and M.-K. helped the AFM analysis. R.-S. and F.-C. synthesized the bulk InSe crystal. C.-A. and W.-H. helped with the electrical measurement. S.-S. helped the article modification. C.-W. supervised the whole project and wrote the article with Y.-R. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by Minster of Science and Technology (MOST), Taiwan (Project No. 103-2119-M-002−021 -MY3) and Taiwan Consortium of Emergent Crystalline Materials (TCECM).
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REFERENCES
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DOI: 10.1021/acsphotonics.7b01030 ACS Photonics 2017, 4, 2930−2936
