Plasmonic Enhanced Performance of an Infrared Detector Based on

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Plasmonic enhanced performance of infrared detector based on carbon nanotube films Huixin Huang, Fanglin Wang, Yang Liu, Sheng Wang, and Lian-Mao Peng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01301 • Publication Date (Web): 21 Mar 2017 Downloaded from http://pubs.acs.org on March 26, 2017

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ACS Applied Materials & Interfaces

Plasmonic enhanced performance of infrared detector based on carbon nanotube films Huixin Huang†, Fanglin Wang‡, Yang Liu†, Sheng Wang‡,* and Lian-Mao Peng†,‡,* †

Academy for Advanced Interdisciplinary Studies, Peking University, Beijing

100871, China ‡

Key Laboratory for the Physics and Chemistry of Nanodevices, Department of

Electronics, Peking University, Beijing 100871, China *

Address correspondence to [email protected] and [email protected]

Abstract: Carbon nanotube (CNT) has been proved to be a promising material in infrared detection, due to many advantages on high mobility, strong infrared light absorption and carriers’ collection efficiency. However, the absorption restriction from single layer limits effective utilization of incident light. In this paper, we introduce a plasmonic electrode structure in CNT thin film photodetector based on random deposited high-purity semiconducting CNT, which can collect photo-induced carriers effectively and enhance light absorption at the same time. The largest enhancement of photocurrents can be achieved at 1650 nm wavelength with suitable plasmonic structure size. Especially, we further discuss the influence of plasmonic structures on the performance of devices. We demonstrate that the best performance improvement of carbon nanotube detector with plasmonic structure can be enhanced as 13.7 times for photocurrent mode and 5.62 times for photovoltage mode than those devices without structure at 1650 nm resonant wavelength. At last, the plasmonic structures are applied on tandem photodetectors with nine virtual contacts, and both the photocurrent and photovoltage are increased. The application of plasmonic electrodes can improve detector performance and remain compact devices structure, which

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shows great potential for optimizing infrared detectors based on nanomaterials.

Keywords: carbon nanotubes, infrared detectors, plasmonic, responsivity, detectivity

1. Introduction Nowadays most scientists pursue the performance improvement of infrared (IR) detectors for single element devices or focal plane arrays, with the appeal of room temperature operation, low cost and more convenient to use.1 Although many kinds of IR detectors used today such as HgCdTe, InGaAs and Ge detectors have shown a relatively high performance, they all have some disadvantages to deal with, such as complex cooling system, large material and fabrication cost for production, and incompatible with silicon circuit process. Carbon nanotube (CNT) has shown great potential in infrared detection, due to its unique physical properties.2, 3 First of all, CNTs have been demonstrated as the darkest materials,4 and its absorption coefficient is about an order of magnitude larger than those conventional materials used for infrared detection such as HgCdTe and InGaAs.5 Secondly the CNTs possess a remarkable mobility for both electrons and holes,6 which enable ultrafast carriers’ collection and response. Furthermore, the energy band structure of CNTs can vary with chiral vectors (m, n), corresponding to different IR band detection.7 The CNT photodetector also has a large linear dynamic range over 120 dB.8 So a well-designed CNT based photodetector can possess all the advantages, such as a barrier-free bipolar diode (BFBD) construction with Palladium (Pd) for the p-type ohmic contact and Scandium (Sc) for the n-type ohmic contact.9-11 The simple process of BFBD device is compatible with CNT based electronic circuit and compact photodiode with channel length scaling down to 50 nm,12 which shows great potential for future optoelectric integration. Because of the appearance of high purity of semiconducting CNTs produced by solution-process methods,13,

14

we can use the CNTs film to construct uniform

detectors array with high performance.15, 16 However, even with the high conversion


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efficiency ~ 60% for a diode based on single CNT has been demonstrated in recently by our group,17 the external quantum efficiency is still low for thin film due to limited absorption. Although a single layer of CNTs film with thickness few nanometers can absorb ~2.3% of incident light, it requires nearly 100nm thickness to achieve full absorption. But, with that thickness of CNT film, the effective photocarriers dissociation and collection of carriers is very difficult to realize simutaniously.18This problem becomes a main obstacle for nanomaterial photodetectors especially for low dimension material such as CNTs, graphene and single-layer MoS2. To conquer this problem, many groups have developed some different methods.19-21 One possible way is by designing specific plasmonic structures which enhance the light absorption at some area overlapping with built-in field. Plasmon resonances represent collective oscillation of conduction electrons at a metallic interface or in small metallic structures induced by incident electromagnetic radiation.22 By selecting different plasmonic structures, such as antennas, clusters, periodic structures and metamaterials, one can manipulate and concentrate the incident light in different ways.23-27 Combining the IR detectors with plasmonic structures can utilize efficiently the incident photons by localizing light at special area. While usual methods to realize plasmonic detectors are fabricating the plasmonic structures on functional material for increasing light absorption. Some groups have used Au particles,28, 29 Au nanodisks,30 periodic Au nanoarrays31 and so on to enhance photocurrent by localizing incident light in the near field for nanomaterials. In the researches mentioned above, most of the plasmonic structures with periodic design are placed at the middle of device channel, which is not suitable for compact IR detectors. And the corresponding wavelength for enhancement ranges from 500 nm to 800 nm, which is hard to extend to short wave IR. While by designing the plasmonic structures combined with electrodes, it can provide a solution to the problems mentioned above. Thus the plasmonic electrodes can localize the light near the electrode and collect effectively photon-induced carriers at the same time. Early reports have shown the potential use of plasmonic electrodes for nanoscale Ge and graphene detectors. 32-34



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In this paper, we use a plasmonic electrode structure to enhance CNT absorption of incident light. For a typical BFBD device, the main photocarriers dissociation area locates near electrodes,17,35 which is exactly the plasmonic enhanced area when the regular Pd/Au electrode is replaced by the plasmonic electrode. We find that the scanning photocurrent spectra show an enhancement peak at about 1650nm matching with the simulating results. Further investigation shows that the enhancement of photocurrent can be tuned by gate voltage. The strongest plasmonic effect occurs at one particular polarized direction that parallel to the electrodes. When the polarized direction of incident light is perpendicular to the electrodes, the responsivity of plasmonic device remains as strong as that of regular devices. This indicates that our plasmonic devices can utilize all kinds of polarized incident light efficiently, without loss at some certain polarized direction. Furthermore the plasmonic electrodes can be applied as the virtual contacts in the tandem photodetectors, in which both enhancements of photovoltage and photocurrent are observed.

2. Materials and Methods 2.1 Materials and devices fabrication The raw arc-discharged CNTs were dispersed through conjugated polymer molecules (9-(1-octylonoyl)-9H-carbazole-2, 7-diyl also known as PCz) in o-xylene solution. The CNTs were ultrasonicated with ultrasonic processor for 30 min and then were centrifuged at 20000g for 1h to remove bundles. The supernatant CNTs were collected and centrifuged at 50000g for 2 h to purify semiconducting CNTs for fabrication of devices. The semiconducting CNTs materials were supported by HuaTan Company, China. CNT network films were deposited on silicon wafer coverd with a 500-nm-thick oxide layer in o-xylene for more than 24 h. After that the silicon wafer was taken from the solution and purged with 99.999% N2. The devices were fabricated by using electron beam lithography (EBL). The electrode Sc (80 nm) and Pd/Au (2/20 nm) contacts were deposited using electron beam evaporation. The used plasmonic and regular devices were made uniformly on the same substrate. The CNT film around electrodes is etched by oxygen plasma to avoid current leakage. For


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long-term stability, we coated a PMMA layer ~ 180nm on the devices. We exposure the pads of devices only for measurement, leaving the contacts covered by PMMA layer. 2.2 Measurement of devices The Raman spectra are collected by Raman system (Jobin Yvon/Horiba Company) with a laser wavelength of 633nm. The electrical and photoelectric properties of the devices were tested using Keithley 4200 and a phase-locked amplifier. A super-continuous spectrum laser (NKT Company) was also used to obtain the photocurrent spectra. The IR wavelength of the laser could be tuned from 1065 nm to 2100 nm.

3. Results and discussion The uniform CNTs film was prepared by depositing the solution-processed high purity semiconducting CNTs on the p+ doped silicon substrate cover with 500nm oxide layer. The diameter of most CNTs is estimated ~ 1.6 nm based on Raman characteristics and E11 exciton transition energy is about 0.7eV in semiconducting CNT films. For regular devices, asymmetric Pd/Au and Sc electrodes are fabricated on the CNTs film and an oxygen reactive ion etching is used to etch unwanted CNT. While for plasmonic devices, we use plasmonic electrodes replace regular electrodes at the Pd/Au end. Figure 1a shows a scanning electron microscopy (SEM) image of a typical plasmonic device at small magnification. In Figure 1a, grey area in the middle of image is CNTs film, with the etched area shown white at left and right side of the film. The black electrode is deposited Sc contact and the white Pd/Au electrode is made by bottom Pd and top Au layer with thickness 2 nm and 20 nm respectively. In the double layer Pd/Au electrode, the 2 nm-thickness Pd layer is used to form effective p-type ohmic contact with CNT film and plasmon resonances are mainly induced at the surface of Au layer. In our experiment, the total width of channel is 10 micrometers long and all the devices are coated by polymethyl methacrylate (PMMA) for stability. Figure 1b shows details of a typical device by enlarging the central area in Figure 1a. In Figure 1b, the plasmonic electrode is designed as periodic axe-like



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structures with the period of ~ 525 nm in which the widest part of the axe structure is ~ 350 nm. So the channel length of the devices is defined by the shortest distance from the Pd/Au plasmonic electrode to the Sc electrode, which is about 200 nm, same as the length of the channel of regular devices as shown in Figure 1c. The largest distance from the plasmonic Pd/Au electrode to the Sc contact is ~ 350 nm. Both plasmonic devices and regular devices are fabricated on the same CNTs film uniformly. Simulation results of plasmonic structure shown in Figure 1d are calculated by COMSOL Multiphysics software using the finite-difference frequency-domain (FDFD) methods. The plasmons are triggered by the incident polarization which is parallel to the Sc electrodes. Under this stimulation, plasmonic near field occurs between the adjacent axe-like structures and the enhanced area mainly locates around the corners of the axe-like structure in Figure 1d. As the thickness of Au layer is only 20 nm, the plasmonic near field at the top of Pd/Au electrode is also close to the silicon oxide substrate where CNTs film locates on. This means that the CNTs film can effectively utilize the stimulated plasmonic near field energy. Further simulation with different wavelength shows the plasmonic resonance peaks at ~1670 nm. The enhancement is calculated based on integrating electric field intensity of the entire area near the plasmonic electrodes divided by the intensity near the Pd electrode in the regular devices. So the ratio can be regarded as the reasonable prediction for plasmonic enhancement. Figure 1f shows a typical rectifying characteristics for a plasmonic device in which a short-circuit photocurrent of 1.08 nA is obtained under 1650 nm laser with the power density of 79 W/cm2. All the plasmonic and regular devices are then tested by chopper-modulated continuum laser with the wavelength from 1200 nm to 2100 nm, and the photocurrent at zero bias are measured by phase-locking amplifier. For the plasmonic devices, the photocurrent enhancement is very limited under illumination with polarization perpendicular to Sc electrodes (more details are shown in Figure S4, Supporting Information). In the following section, we mainly discuss the photocurrent enhancement for plasmonic devices under illumination with polarization parallel to Sc electrodes.


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The results shown in Figure 2a are the average photocurrent spectra for all the tested plasmonic and regular devices at Vg= 0 V. When polarization of incident light is parallel to the electrodes, the photocurrent spectra of regular devices (the blue curve) show no obvious peak around 1650 nm, with nearly flat response from 1500 nm to 1800 nm wavelength. However, for plasmonic devices, the photocurrent spectra show distinct resonance response peak around 1650 nm, which is exactly locating around the resonant position predicted by simulation ~ 1670 nm (Figure 1e). When the photocurrent spectra of plasmonic devices are divided by those of regular devices, we obtain the enhancement curve for different wavelength as shown in Figure 2b (blue curve, Vg= 0V), with the maximal enhancement of 4.3 times appearing at 1680 nm wavelength. When the gate voltage Vg= 40 V, the enhancement can be increased larger as shown in Figure 2b (red curve, Vg= 40 V). The largest enhancement is about 13.7 times at 1640 nm wavelength, which is about three times larger than that at Vg= 0V with the same resonance peak. The increasing enhancement is mainly caused by the change of the effective dissociation area by adjusting the applied gate voltages. At Vg= 0V, the main dissociation area locates not only at the zone near the Pd/Au electrode, but also exists near the n-type electrode as shown in Figure 2c. In this case, plasmonic electrodes mainly contribute to one part of the effective exciton absorption and dissociation area, which is near the Pd/Au electrode. But the exciton dissociation near the Sc contact cannot be sufficiently increased by the plasmonic field due to relative weak field distribution. So the actual enhancement mainly comes from the plasmonic enhanced Pd/Au contact area, which causes the relative low enhancement. However, for Vg= 40V, the energy band in channel is changed by applied gate voltage which flattens the energy band near the Sc contact and sharpens the energy band near the Pd/Au contact as shown in Figure 2d. That means the exciton dissociation area overlaps effectively to the plasmonic enhanced field, increasing the photocurrent enhancement. With the larger positive gate voltage, the energy-band bending near the Pd/Au electrode is steeper, which improves the dissociation efficiency of photon-induced excitons due to strong local electric filed. If the gate voltage becomes negative, the enhancement decreases as shown in Figure S5 in Supporting Information.



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These results suggest that the plasmonic enhanced area coincides with photo-induced carrier generation and separation region. The photocurrents depending on the polarization are shown in Figure 2e and Figure 2f. Although the nanotubes in network CNTs film are random deposition without alignment, the regular devices show a typical polarization-dependence to incident light (green dots shown in Figure 2e). The photocurrent dependence on the polarization angle is mainly due to that most nanotubes in the ~ 200 nm short channel are tending to align as the SEM images shown in Figure 1b and 1c. The localized directional arrangement of CNTs makes the photocurrent of the regular devices depend on the polarization angle. We defined the depolarization ratio as

rp = Ipperpendicular I pparallel ,

(1)

where I parallel is the maximal photocurrent under one of all polarization and p I perpendicular is the photocurrent under the polarization that has turned 90 degrees from p the polarization in I parallel . If the ratio is small, it means the devices show a good p polarized response. In Figure 2f, the depolarization ratio rp is about 0.2 in regular devices (blue curve), which is coincide with the cos-squared function features under all polarization. But for plasmonic devices, the rp is ~ 0.9 (red curve in Figure 2f). As a result, the polarization response for plasmonic devices shows an almost circular feature in Figure 2e. The photocurrent of plasmonic devices is almost equal to the maximal of the regular devices. This is due to the enhancement by the plasmonic structures raising the response that parallel to the electrodes. So the plasmonic devices show inconspicuous polarization dependent response, which is very important for common IR detection with random polarization. To further investigate the plasmonic enhanced performance of devices with longer channel length, we fabricated the plasmonic and regular devices with 500nm channel length. As the channel length increase, the zero-bias resistance becomes larger which results a better performance than that of short channel-length devices (Figure S7 and S8, Supporting Information). Meanwhile 500 nm channel can still


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maintain a strong plasmonic effect and also result a relative large depolarization ratio about 0.59 as shown in Figure S9 in Supporting Information. So we use the 500 nm channel devices to investigate the plasmonic enhancement induced improvement of the performance of network CNTs film detectors. We have considered both photocurrent and photovoltage mode and all devices are measured under 1650 nm laser. In Figure 3a and 3b, the photocurrent increases linearly with incident power density and the photovoltage becomes saturated at high power density. Clearly under plasmonic effects, the plasmonic devices show a better performance in both cases. At low power density, the photocurrent and photovoltage of plasmonic devices are about an order of those regular devices. Further we can calculate the responsivity of both kinds of devices. The photocurrent responsivity is defined by

R i = I s Pin ,

(2)

where the Is represents the measured photocurrent, and the Pin represents the power of incident light on the devices. And the photovoltage responsivity is defined by

R v = Vs Pin ,

(3)

where the Vs represents the measured photovoltage. Figure 3c and 3d show the photocurrent and photovoltage responsivity. The photocurrent responsivity shows almost a constant, while the photovoltage responsivity increases with decreasing power density and appears nearly saturated when power density is below 0.25W/cm2 for regular devices. But for plasmonic devices working at photovoltage mode, photovoltage responsivity shows an increasing trend under weak light, and saturates when power density is below 0.03W/cm2. The responsivity for plasmonic devices is 7.9 mA/W in photocurrent mode and 3.5×107 V/W in photovoltage mode, while for regular ones, the photocurrent responsivity is 0.93 mA/W and the photovoltage responsivity is 4.7×106 V/W. The plasmonic device has much higher responsivity than that of regular one due to the enhanced localized light by plasmons. To evaluate the performance of an IR photodetector, noise spectral density must be analyzed first. For a photovoltaic detector, the noise mainly comes from the



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Johnson noise, the shot noise and the flicker noise.36 The Johnson noise is also known as thermal noise, which is caused by the thermal motion of the charge carriers in a resistive element. So the Johnson noise exists regardless of applied voltages. The shot noise is associated with the direct current flowing across a potential barrier and originates from the discrete nature of electric charge. Flicker noise is also known as the 1/f noise and always relate to the applied direct current, which means a bias applied on the device. At zero bias condition, no reverse direct current flow through the device. So both the shot noise and flicker noise can be negligible in our devices, and the Johnson noise dominates in noise current spectral. For Johnson noise, the noise current is defined by

ij =

4kT ∆f , Rd

(4)

And the noise voltage is defined by

Vj = 4kTRd ∆f ,

(5)

where the k is Boltzmann constant, T is the temperature, ∆ f is the frequency bandwidth, and Rd is the zero-bias differential resistance of diodes, which is defined by

 ∂V  Rd =   .  ∂I V =0

(6)

For the 200 nm channel devices, the relative small R d makes it possible to measure the noise current. The calculated Johnson noise current is approaching to the measured data at different gate voltages (Figure S6, in Supporting Information). This means it is reasonable to consider the Johnson noise as the principal noise source which is the main factor to restrict the specific detectivity of our devices. The maximum of Rd for 500 nm channel-length device appears at Vg = 0V as shown in Figure S8. In this condition, the calculated noise currents for plasmonic and regular devices are 1.21 fA and 1.65 fA respectively. The calculated noise voltages for plasmonic and regular ones are 13.6 µV and 10.1 µV. Both the noises voltage and noises current for plasmonic devices are similar with the regular ones, suggesting that


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our plasmonic electrodes do not include extra noise sources into the devices. Based on the responsivity and noise spectra, we can obtain the specific detectivity (D*) by the equation:

D* =

R A∆f , noise

(7)

where R and noise is responsivity and noise figures for photocurrent or photovoltage mode, ∆f is 1Hz. From equation 7, we obtained the Di*(D* for photocurrent mode) is 1.46×109 cmHz1/2/W (Jones) for plasmonic devices and 1.28×108 Jones for regular ones respectively. So the largest detectivity enhancement is about 11.4 times for photocurrent mode. As for photovoltage mode, the Dv* is 5.79 × 108 Jones for plasmonic devices and 1.03×108 Jones for regular ones. So the enhancement for photovoltage is 5.62 times, which is less than that of the photocurrent mode due to the nonlinear relationship between photoresponse and power density in photovoltage mode. As the Dv* decrease rapidly with increasing power density, the Di* is a constant for photodetection. To further demonstrate the performance enhancement of plasmonic structure, the plasmonic electrodes are designed as virtual contacts in BFBD devices as shown in Figure 4a. Virtual contacts are used to multiply the photovoltage response of BFBD photodetectors which can raise the signal noise ratio and output a large signal under same incident power.35 Figure 4a shows an SEM image of tandem photodetector with nine plasmonic virtual contacts. In the tandem devices, the regular Pd/Au electrodes are all replaced by plasmonic contacts with the same geometrical features discussed above. The photoresponse for plasmonic and regular devices are shown in Figure 4b, with an incident power density of 118.3 W/cm2 at 1650 nm laser. The open-circuit photovoltage is 2.16V for regular virtual contacts and 2.89V for plasmonic ones. Meanwhile the short-circuit photocurrent is 1.53nA for regular virtual contacts and 8.79nA for plasmonic ones. Both photovoltage and photocurrent show an obvious increase by plasmonic enhanced effects, which can further raise the signal noise ratio



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and enable a larger output signal. For state-of-art CNT-based detectors, photovoltaic detectors have better performance than photoconductive detectors.16,20,21,37-39 Xie et al. reported CNT-based bulk-heterojunction photovoltaic detector with D* ~ 9×1011 Jones at 860 nm, which has the highest detectivity for CNT-based detectors.37 However, to achieve high detectivity, the heterojunctions should be formed effectively, which usually restricts the detectable wavelength and most of bulk-heterojunction cannot response beyond 1500 nm wavelength. For CNT photovoltaic detector based on BFBD structure, the detectors can detect the whole range of short-wavelength IR (1 - 3 µm) because the photoresponse band is determined by the intrinsic E11 exciton absorption of CNT which can be tuned by the diameter of CNT. Furthermore, photoresponse performance for some special wavelength can be improved by introducing the plasmonic electrodes. Although thick CNT films are used in the CNT based bulk-heterojunction detectors, the exciton dissociation area is near the junction interface and the carriers are easy to lose during transport, which means that the external and internal quantum efficiency cannot be achieved at the same time.38 However, in BFBD devices, the exciton dissociation area is near the Pd and Sc contacts, indicating that the carriers loss can be suppressed efficiently. For traditional state-of-art detectors for shortwave IR detection, the devices based on p-n junction have been optimized to about 1011~1012 Jones (commercial InGaAs detectors) with external quantum efficiency larger than 60%.1 While for devices based on BFBD structure have relative low quantum efficiency (< 1%) due to the limited absorption with few nm thickness and photo excited charges loss caused by impurities in device channel. By increasing the thickness of CNT film, the performance of detectors can be improved further.

4. Conclusion We use the periodic axe-like plasmonic electrodes to enhance the performance of IR detectors based on network CNTs film. Our results show that the plasmonic enhancement resonate around 1650nm wavelength well corresponding to our simulation, which is a short-wave IR for plasmonic enhancement application. Further


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investigation shows that the plasmonic enhancement changes with the applied gate voltage which proved the plasmonic enhanced area overlap with photocarriers generation region. The polarized response means the devices can utilize all the incident power under different polarization even at a short channel with most CNTs perpendicular to the electrodes. Further we have discussed the enhanced performance arise from plasmonic effects by research the responsivity, noise and specific detectivity for plasmonic and regular devices with photocurrent or photovoltage mode. The maximal Di* for plasmonic devices is 1.46×109 Jones and 11.4 times of regular devices. By further improving the structure and the quality of CNTs film, such as dense semiconducting CNTs array with thicker layer, the plasmonic detectors will show more powerful use in modern room temperature IR detection and even in optical integration circuit with compact construction.

ASSOCIATED CONTENT

Supporting information The Supporting Information is available free of charge on the ACS Publications website http://pubs.acs.org. Figure S1 shows an atomic force microcopy (AFM) image and absorption spectra of deposited CNT films. Figure S2 shows the Raman feature of CNTs films. Figure S3 shows 30 statistical photocurrent enhancement results. Figure S4 shows the photocurrent feature for devices under polarization perpendicular to the electrodes. Figure S5 shows that the photoresponse enhancement changes with applied gate voltages. Figure S6 shows the noise feature for 200 nm short channel devices. Figure S7 shows a 500 nm channel device with good performance. Figure S8 shows the zero-bias differential resistance for 200nm channel and 500nm channel devices. Figure S9 shows the polarization response for 500nm channel device. Figure S10 shows the different geometrical parameters of plasmonic electrodes with different enhancement feature.



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AUTHOR INFORMATION Corresponding Authors * E-mail: [email protected]. * E-mail: [email protected]

Acknowledgments This work was supported by the National Key Research & Development Program (Grant No. 2016YFA0201902) and the National Science Foundation of China (Grant Nos. 61370009 and 61621061).

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Single-walled Carbon Nanotubes with Full Surface Coverage for High-performance Electronics. Nat. Nanotechnol. 2013, 8, 180-186. 15. Jain, R.M.; Howden, R.; Tvrdy, K.; Shimizu, S.; Hilmer, A.J.; McNicholas, T.P.; Gleason, K.K.; Strano, M.S. Polymer-Free Near-Infrared Photovoltaics with Single Chirality (6, 5) Semiconducting Carbon Nanotube Active Layers. Adv. Mater. 2012, 24, 4436-4439.

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Barrier-Free

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(b)

(d)

(e)

(c)

(f)

26

enhancement simulation

24 22 20 18 16 14 12 10

0.5 0.4 0.3 0.2 0.1

DrainI (nA)

(a)

enhancement

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


DrainI (µA)

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2 1 0 -1 -2

1600

1800

2000

2200

wavelength(nm)

-0.1

dark 1650nm laser

0.0

0.1

DrainV (V)

0.0 1400

plasmonic BFBD

-0.4

0.0

0.4

0.8

1.2

DrainV (V)

Figure 1. (a) SEM image of a plasmonic device. The grey color zone is CNTs film. (b) Magnified image of plasmonic device shows the details and (c) SEM image of a regular device with 200 nm channel length, the top and bottom contacts are Sc and Pd/Au electrodes respectively. (d)Simulation of plasmons distribution in Pd/Au electrodes. The top simulation is from top view in z direction perpendicular to the substrate and the bottom simulation is from side view in y direction. (e) The enhancement curve calculated from integrated electric field intensity of the total area near the plasmonic electrodes divided by the intensity near the Pd/Au electrode of the regular devices. The resonance plasmons peak takes place at 1670nm. (f) I-V curve of a plasmonic BDBD device in dark. Inset figure shows the comparison of I-V curves in dark and under illumination of 1650 nm laser.



8 6 4 2 0 1200 1400 1600 1800 2000 2200

(d)

wavelength (nm)

16 14 12 10 8 6 4 2 0

(c) Plasmonic/Normal Vg=40V Plasmonic/Normal Vg=0V

1200 1400 1600 1800 2000 wavelength (nm)

(e)

0 30

photocurrent (a.u.)

1.0 0.5

330

300

60

270

0.0 90 0.5

240

120 1.0

(f)

150

180

1.2

regular plasmonic

210

photocurrent (a.u.)

10

(b) 18

plasmonic device regular device

enhancement

(a) 12 photocurrent (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.0 0.8 0.6 0.4 regular plasmonic

0.2 0.0

0

50 100 150 200 250 300 350 rotation(degree)

Figure 2. (a) The photocurrent spectra for plasmonic device (red curve) and regular one (blue curve) under illumination with polarization parallel to electrodes. (b) The plasmonic enhancement spectra at Vg= 0V (blue curve) and 40V (red curve). Energy band diagram of device for (c) Vg= 0V and (d) 40V. (e) (f) Photocurrent as a function of polarization angle of the incident light for plasmonic device. The regular device exhibits the largest photocurrent when the polarization of the incident light is nearly perpendicular to the electrodes (~ 0° and ~ 180°) and the smallest photocurrent is observed when the polarization is nearly parallel to the electrodes (~ 90° and ~ 270°).


Page 21 of 22

(a)

photovoltage(V)

photocurrent(A)

100

(b)

10-10 10-11 -12

10

regular plasmonic

-13

10

10

-3

(c)

10

-2

-1

10

10-3

regular plasmonic

-4 -3

10

(d)

power density (W/cm^2)

10

-2

10

-1

10

0

10

1

power density (W/cm^2) 8

10

Rv (V/W)

10

10-3

107

regular plasmonic

-4

10

-1

10-2

10

0

10

10

-2

Ri (A/W)

10

-3

-2

10

10

-1

regular plasmonic

6

10

0

10


10-3

10-2

10-1

100


Figure 3. Photoresponse for plasmonic and regular devices with channel length 200 nm. The short-circuit photocurrent (a) and the open-circuit photovoltage (b) versus power density of 1650nm incident light. (c) (d)The photocurrent responsivity and photovoltage responsivity versus power density. (a)

(b)

2 0 -2

Id(nA)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-4 -6 -8

regular device plasmonic device

-10 -12 -1

0

1

2

3

Vd(V)

Figure 4. (a) The SEM image for tandem photodetectors with plasmonic electrodes. Nine virtual contacts are introduced to construct the tandem devices. (b)The photoresponse for tandem devices with regular and plasmonic electrodes under excitation of 1650 nm laser.



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TOC


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Plasmonic Enhanced Performance of an Infrared Detector Based on

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