Sensitivity Enhancement of Si Nanowire Field Effect Transistor

Letter pubs.acs.org/NanoLett

Sensitivity Enhancement of Si Nanowire Field Effect Transistor Biosensors Using Single Trap Phenomena Jing Li,† Sergii Pud,† Michail Petrychuk,‡ Andreas Offenhaü sser,† and Svetlana Vitusevich*,† †

Peter Grünberg Institute(PGI-8), Forschungszentrum Jülich, Jülich 52425, Germany Radiophysics Faculty, Taras Shevchenko National University of Kyiv, 03022 Kyiv, Ukraine

‡

S Supporting Information *

ABSTRACT: Trapping−detrapping processes in nanostructures are generally considered to be destabilizing factors. However, we discovered a positive role for a single trap in the registration and transformation of useful signal. We use switching kinetics of current fluctuations generated by a single trap in the dielectric of liquid-gated nanowire field effect transistors (FETs) as a basic principle for a novel highly sensitive approach to monitor the gate surface potential. An increase in Si nanowire FET sensitivity of 400% was demonstrated. KEYWORDS: Nanowire, field effect transistor, single trap, random telegraph signal (RTS) noise, biosensors i nanowire (NW) field-effect transistors (FETs) have attracted increasing attention during the past decade due to their unique capability of probing chemical and biological species for clinical diagnostics, drug discovery, and genomics applications.1−10 The mechanism of sensing is based on the changes of sensor conductance in response to the specific binding of (bio) chemical molecules to the sensor inducing a potential change on the gate oxide surface.11 The detection limit of such sensors is constantly being improved by miniaturizing the dimensions of the NWs, which results in an increase of the sensor surface control over the nanochannel current.12 Moreover, Si NW FETs can be fabricated using the top-down fabrication strategy, which is CMOS-compatible and promises easy integration and high cost efficiency.13 Therefore, Si NW FETs are perfect candidates for the development of highly sensitive, selective, and label-free sensors for the realtime detection of (bio) chemical species. However, the downscaling of Si NW FETs while maintaining the quality of the device surfaces leads to an increase in the low-frequency noise, due to decreasing numbers of charge carriers and increasing surface contributions to electric noise.14 Usually, low-frequency noise is a major limitation factor determining the sensitivity of the sensor. Several approaches are therefore used to overcome this problem in nanoscale devices: improving the quality of the device surfaces,15,16 using frequency domain

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© XXXX American Chemical Society

detection,17 and optimizing the operating regime of the device.18−22 Despite traditional sensing approaches, the low-frequency noise itself can be regarded as a source of useful information about the analyte. At low frequencies, the power spectral density (PSD) of drain current fluctuations in FETs often follows the 1/f law, known as flicker noise.23 The nature of the 1/f noise is still under debates.23,24 However, flicker noise for broad range of nanoscale FET devices can be well described in frame of number and correlated mobility fluctuation model.25 The drain current fluctuations of the NW are generated by random trapping and detrapping processes of charge carriers to the traps randomly distributed in the gate oxide close to the Si NW channel.26 Downscaling of the device usually leads to a reduction in the absolute quantity of traps, and as a result the PSD decomposes from the 1/f law into several Lorentzianshaped components.27 With further shrinking of the device dimensions, a certain size may be reached when the current in the device is only influenced by a single trap in the gate dielectric layer. In this case, switching of the drain current between two distinct levels under constant drain source and Received: March 21, 2014 Revised: April 25, 2014

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dx.doi.org/10.1021/nl5010724 | Nano Lett. XXXX, XXX, XXX−XXX

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gate source voltage is observed.12,26,27 These fluctuations, known as random telegraph signals (RTSs), are often observed in small-area metal-oxide-semiconductor (MOS) transistors27 and in liquid-gated transistors.28 They give a Lorentzian distribution in the PSD of the drain current noise.27 The times that the drain current spends at a certain level are called characteristic time constants and correspond to the capture and emission times of the trap. According to the Shockley−Read− Hall model, the capture time is inversely proportional to the drain current. In some cases, the capture time constants of the RTS noise may exhibit even stronger dependence on drain current.29,30 In electronics and conventional time-domain analysis, the RTS is regarded as an unwanted effect because of the instabilities introduced by switching between distinct current levels26 and thus a great deal of effort have been expended on avoiding RTS in electronic applications.31,32 The possible utilization of RTS phenomena as a source of information has not been considered yet. In this work, we demonstrate that single-trap phenomena in liquid-gated Si NW FET can be used as an effective and versatile approach for biosensing. It is revealed that the characteristic time of single-trap switching kinetics is highly sensitive to the surface potential determined by different pH values of the gating solutions. The sensitivity of the proposed method is shown to be considerably higher than for conventional drain current measurements and can be further improved by a special design of the structures. The structures under study were liquid-gated Si NW FETs fabricated at the Helmholtz Nanoelectronic Facility of Forschungszentrum Jülich (Germany). The scanning electron micrograph (SEM) image of a 0.5 μm long and 100 nm wide Si NW FET is shown in Figure 1A. For the fabrication of the devices, we used a silicon-on-insulator (SOI) substrate with a 70 nm ⟨100⟩ oriented top silicon layer, 145 nm thick buried oxide (BOX) layer and a 675 μm substrate. The top active silicon layer of the wafer, initially doped with boron at a level of 1015 cm−3, was first thinned down to 50 nm by forming a thermally grown layer of 37 nm SiO2, which after patterning served as a mask for later etching of the Si NW. Silicon nanowire structures are then written using electron beam lithography (EBL) in the HSQ resist. After development, the structure was transferred to the silicon oxide mask by reactive ion etching (RIE). In order to obtain smooth surfaces of NWs and avoid increased gate dielectric trap density,5,16 we used tetramethylammonium hydroxide (TMAH) anisotropic wet etching to define our nanowire devices. To protect the interface between the nanowire channel and gate oxide from ion implantation damage, a 5 nm thick SiO2 protection oxide layer was grown using thermal oxidation at 1000 °C. Boron ion implantation was then performed to fabricate the source and drain ohmic contacts to the nanowires with an energy of 7 keV and a dose of 1 × 1015 cm−2. After this, the damaged protection oxide was removed by immersing the sample in diluted HF solution. It results in a different thickness of BOX layer, seen as a dark blue stripe in Figure 1A. Next, a 9 nm thick gate oxide layer was grown in a thermal furnace at 1000 °C for protection against the liquid. The drain/source contact pads and the back gate electrodes (300 nm Al layers) were fabricated using photolithography, electron-beam evaporation and a lift-off process. In order to decrease the contact resistance, an annealing process was carried out for 10 min at 400 °C in a forming gas (H2/N2) atmosphere. Devices were wire-bonded on chip carriers and encapsulated using glass rings and

Figure 1. (A) False-colored SEM image of a Si NW FET device. (B) Transfer characteristics of the Si NW FET measured at VDS = −0.1 V at different pH values in linear and logarithmic scale. The length of the Si NW FET is 500 nm and the width is 100 nm.

poly(dimethylsiloxane) (PDMS). The fabricated Si NW FET devices represent accumulation FET with p+−p−p+. It should be noted that here we present the results of experiments with Si NW FETs of 500 nm length and 100 nm width. However, the effects we show are also observed in samples of various sizes. The transport properties of the Si NW FET were measured in typical biocompatible 0.1 M solution of phosphate-buffered saline (PBS) at a certain drain source voltage, VDS, and different gate voltages, VG, using a semiconductor parameter analyzer (K4200, Keithley). An Ag/AgCl electrode was used to set the potential of the liquid gate. In order to demonstrate the sensitivity of the Si NW FET biosensor, we changed pH of the liquid gate (from 5.0 to 8.5) while maintaining the ionic strength constant. The corresponding transfer curves are shown in Figure 1B. The Si NW FETs display p-type FET behavior with a subthreshold slope of 130 mV per decade and the Ion/Ioff ratio reaches 105 at VDS = −0.1 V. The drain/source voltage, VDS, as well as the liquid gate voltage, VG, were set against the grounded source of the NW. The transfer curve shift is correlated to the pH value and the threshold voltage (VTh) of the device increases with pH as is shown in Figure S2, Supporting Information. The sensitivity of the Si NW FET device to the pH is found to be in the range of 25 to 37 mV/ pH, which is a typical value33 for FETs using nonmodified SiO2 as the gate insulator. Noise spectra and time traces were measured using an ultralow-noise homemade preamplifier (equivalent thermal noise of 1.4 nV/Hz1/2 at 100 Hz) and an HP 35670A dynamic parameter analyzer (Hewlett-Packard). The drain current, ID, was calculated using the difference in readings of two voltmeters (see Figure S1, Supporting Information) and the B


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where τ is the time constant measured from RTS spectrum and τc and τe are capture and emission times, respectively. An average lifetime of the carrier in a free state before the capture to the trap corresponds to the capture time constant, τc, whereas the emission time,τe, is the average time spent by the carrier in the captured state. According to the classical Shockley−Read−Hall model34,35 for an active center the time constants can be expressed as follows

value of the load resistance. All measurements were performed at a small drain source voltage, VDS = −0.1 V to ensure the linear regime of operation. As was mentioned above, at submicrometer feature sizes of the transistor, the noise of the conducting channel may be mainly determined by a single trap near the interface between the gate dielectric and the silicon channel. In such a case, RTS noise is often observed. The noise spectra of the RTS process can be represented by the Lorentzian function, S( f) = S(0)/[1 + (2πf/f 0)2], where f 0 represents the characteristic frequency of the process. The measured drain current spectral density of Si NW FET contains Lorentzians which shift their characteristic frequency in response to the change in pH. The spectra were measured at the value of VG = −0.9 V, which was optimized in order to maximize the modulation effect of the single trap. The results are shown in Figure 2A in the form of current noise

τc =

1 σpνthp

(3)

τe =

1 1 = e Eb / kT σpvthp1 σpvthNv

(4)

where σp is the capture cross section of the trap, νth is the average thermal velocity of the charge carriers, p is the concentration of free holes at interface, p1 is the statistical factor, which equals density of holes in the valence band when the Fermi level coincides with Eb, the energy level of the center with respect to the top of the valence band, and Nv is the effective density of states in the valence band. As we can see from eq 3, τc is the inverse function of the hole concentration, which can be tuned by VG. At the same time, τe is a weak function of the charge carrier concentration (eq 4). f 0 is a combination of both capture and emission times (eqs 1 and 2) and reflects competition of both characteristic times. It should be noted that according to eqs 1 and 2 the frequency domain detection (f 0) can reflect changes of hole concentration as sensitive as the time domain (τc) under the condition that τc ≪ τe. The τc and τe values can be obtained from the time traces of the drain current (Figure 3A) and the characteristic frequency f 0 (eqs 1 and 2). In order to obtain a relation between τc and τe,

Figure 2. (A) Drain current noise spectral density of Si NW FET multiplied by frequency at different pH values, measured at VGS = −0.9 V, VDS = −0.1 V. (B) Characteristic frequency of the Lorentzian components (data of the panel A) and drain current as a function of pH value.

spectral density multiplied by frequency. This allows compensation of the 1/f noise behavior and provides better resolution of the Lorentzian-shaped component in the spectra. The characteristic frequencies of the Lorentzian components of the spectra are plotted as a function of the pH in Figure 2B. Changing the pH from 5.5 to 8.5 results in changes of the Lorentzian characteristic frequency from 80 to 180 Hz. Such a change is in the same order of magnitude as changes of the drain current from 31 to 61 nA with the pH (Figure 2B). On the other hand, the characteristic frequency f 0 of the Lorentzian component corresponding to the RTS is a function of capture and emission times. It can be expressed as 1 f0 = (1) 2πτ ττ τ= ce τc + τe (2)

Figure 3. (A) Random telegraph signals in a Si nanowire transistor. Typical RTSs time trace registered in our Si NW FET, measured in solution at pH = 7.5. (B) Histogram of the RTS drain current fluctuation (data of the panel A), measured in solution with pH = 7.5. C


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a histogram based on the data of Figure 3B can be used.36 A typical time trace of the RTS noise registered is shown in Figure 3A. The drain current level is changed when a charge carrier from the channel tunnels to the trap in the gate dielectric and is captured there or vice versa; the carrier is emitted from the charged trap to the channel. A corresponding histogram of the drain current time trace is plotted in Figure 3B for more detailed analysis. It shows two distinct Gaussian peaks, indicating two-state switching, which corresponds to the behavior of a single trap near the interface. It should be noted that for different bias conditions these peaks have some overlaps, but τc and τe can be resolved with high accuracy via histogram fitting. At a certain bias condition, the trap resides in the band gap within 2kT of the channel Fermi level, and therefore it is within a favorable energy distance of the channel to be able to capture and emit the channel carriers. The low current level corresponds to the state when a carrier is captured by a trap while the high current level corresponds to the empty state. The time traces of the RTS noise were measured for different values of pH = 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5. The corresponding time traces and histograms are listed in Figure S3, Supporting Information. The height of each peak in Figure 3B is proportional to the time that the system spends in each state. Therefore, the ratio between peak heights corresponds to the relation between capture and emission times. The distance between the peaks equals the RTS amplitude, ΔID. Using relation τc/τe obtained from the histogram and τ obtained from Lorentzian-shaped noise component of the spectra, the values of τc and τe can be calculated using eq 2. The values of capture and emission times as well as the time constant τ were calculated for different pH values and are shown as functions of drain current and pH in Figure 4.

surface potential. According to eq 3, at a certain temperature T, the capture time τ c is inversely proportional to the concentration of free holes p. In the linear mode of operation, which was maintained during measurements, the drain current ID is proportional to the carrier concentration in the accumulation layer, p. In the ideal case of the Shockley− Read−Hall theory, the capture time constant is inversely proportional to the drain current (green line in Figure 4). However, we observed τc ∝ I−3 D , which obviously deviates from the classical Shockley−Read−Hall model. It should be noted that we have measured a set of samples. From these data, we obtain that the slope of τc dependence on ID varies from −2 to −4. Such a strong dependence of capture time on the current in the liquid-gated Si NW FET can be explained by the Coulomb blockade effect in a similar manner to the conventional metal oxide semiconductor (MOS) FETs.26,30 By capturing a charge carrier, a trap in the gate dielectric becomes charged and thus a repulsive center for charge carriers. The capture probability therefore differs significantly for the cases of charged and uncharged traps. The concept is implemented by introducing into the Shockley−Read−Hall model Coulomb blockade energy, ΔE, which an electron (or hole) has to overcome while moving from the channel to the trap in the dielectric.37,38 Thus, eq 3 can be modified as

τc =

1 ΔE / kT e σpνthp

(5)

As we can see from Figure 4, τe does not depend on the current, and thus based on eq 4 we can assume that σp does not depend on gate voltage. The deviation of τc behavior from Shockley−Read−Hall model is caused by the Coulomb blockade energy, ΔE, which is inversely proportional to the logarithm of the carrier density.39 This energy is the difference between free energy of the trap in charged and uncharged state. By decreasing the effective area of the channel to tens of nanometers and below, the influence of the Coulomb blockade effect may be increased dramatically due to the quantization of carriers40 in the channel of liquid-gated FETs. In conventional time domain analysis, the changes of the surface potential are registered as changes of the average value of ID. We measured the drain current change in liquids of different pH (Figure 2B). The ratio of ID and its maximum value Imax D is shown in Figure 5A (black points). It should be emphasized that in our case single-trap phenomena play an important role in electric transport (shown schematically in Figure 5B). The kinetics of drain current modulation by a single trap near the Si/SiO2 interface is strongly dependent on the concentration of free holes due to the Coulomb blockade effect. ID is proportional to the concentration of free holes, which is a function of the surface potential. In the case of the different pH of the liquid gate, the silanol group of the silicon oxide layer performs the function of a receptor for hydrogen ions. Varying the pH from 5.5 to 8.5 changes the surface potential due to the binding of protons to the surface of the dielectric layer. Therefore, the capture time constant of the single trap in the gate dielectric is a strong function of a surface potential. In order to compare the sensitivity of ID and τc to pH, in Figure 5A we also plot relations between τc and τmin in c Figure 5A. As can be seen from Figure 5A, the efficiency of our approach is at least 400% more sensitive than the conventional technique based on the tracking of drain current changes. As

Figure 4. Capture (τc) and emission (τe) time constants and characteristic time constant (τ) of the RTS noise plotted as a function of different pH and drain currents at VDS = −100 mV, VG = −0.9 V. Points are connected with lines as a guide to the eye. Dashed lines indicate different behaviors with slopes: (−3) for our experimental data and (−1) for the conventional Shockley−Read−Hall model.

As can be seen from Figure 4, τc is much more sensitive to the current and thus to pH than τ, which represents characteristic time extracted from spectra measurements. τe in turn is a weak function of the drain current, because it depends only on occupancy of the trap, as was discussed above. The characteristic time τ obtained from the Lorentzian-shaped component of current PSD is a superposition of both capture and emission time constants and is therefore less sensitive to D


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ASSOCIATED CONTENT

S Supporting Information *

(Figure S1) Schematic of the noise measurement setup. The voltage is applied to the sample using a battery loaded on the variable resistor. The current through the sample is calculated using the difference between readings of the voltmeters Vm and Vs. Spectra are acquired using the dynamic signal analyzer HP 35670 (Hewlett-Packard). (Figure S2) Shift in threshold voltage (VTh) with pH values, as extracted from the data shown in Figure 1B. (Figure S3) Typical time dependence (left) and the corresponding histogram (right) of the FET drain-source voltage, measured in solution with pH = 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Stefan Trellenkamp for electron beam writing and the technological staff of the Helmholtz Nanoelectronic Facility for assistance in device fabrication at Forschungszentrum Jülich GmbH. J.L. would like acknowledge financial support from Helmholtz Association and Chinese Scholarship Council (Helmholtz-CSC). S.P. greatly appreciates the research grant from the German Academic Exchange Service (DAAD).

Figure 5. (A) Sensitivity extracted from the pH dependence of the drain current and RTS capture time constant. (B) Mechanism of sensitizing the nanowire pH measurements by the single trap phenomenon.

demonstrated in Figure 5A, the sensitivity increase has considerable room for improvement by a special design of NW structures in order to achieve steeper dependences of single-trap time constants on the concentration of free carriers in the channel. Gate-all-around (GAA) technology can be used to achieve capture time dependence on the current with a power law of up to −13 as was shown for metal-gated NW FETs.41 It should be noted that the demonstrated phenomena are features of the FET devices and occur regardless of the sensing environment. Therefore, changes of surface potential can be registered with increased sensitivity using trap kinetics analysis in all kinds of measurements thus making the proposed method a versatile biosensing tool for applications including the label-free detection of cancer biomarkers, DNA strands and enzymes. In conclusion, we show that fluctuation phenomena related to the single-trap modulation of the drain current can be used as a versatile approach for tracking surface potential changes with increased sensitivity. Liquid-gated Si NW FETs were fabricated with dimensions small enough for a single trap to have a considerable impact on electric transport in the conducting channel. It is shown that the kinetics of the registered two-level switching of drain current in liquid-gated Si NW FETs demonstrates a deviation from behavior according to the Shockley−Read−Hall theory with considerably stronger capture time dependence on drain current. The mechanism of the effect is related to the change in charge state of a single trap and is explained in the framework of the Coulomb blockade concept. The observed phenomenon is used to realize a new detection approach, which is at least 400% more sensitive to surface potential than conventional methods based on the change in value of the drain current. The efficiency of suggested biosensing method can be further improved by a special design of NW FET structures.

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ABBREVIATIONS Si NW, silicon nanowire; FET, field-effect transistor; RTS, random telegraph signal; MOSFET, metal oxide semiconductor FET; PSD, power spectral density

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REFERENCES

(1) Cui, Y.; Wei, Q.; Park, H.; Lieber, C. M. Science 2001, 293 (5533), 1289−92. (2) Zheng, G.; Patolsky, F.; Cui, Y.; Wang, W. U.; Lieber, C. M. Nat. Biotechnol. 2005, 23 (10), 1294−301. (3) Zheng, G. F.; Patolsky, F.; Lieber, C. M. Abstr. Pap. Am. Chem. S 2005, 230, U306−U307. (4) Patolsky, F.; Zheng, G.; Lieber, C. M. Nat. Protocols 2006, 1 (4), 1711−24. (5) Stern, E.; Klemic, J. F.; Routenberg, D. A.; Wyrembak, P. N.; Turner-Evans, D. B.; Hamilton, A. D.; LaVan, D. A.; Fahmy, T. M.; Reed, M. A. Nature 2007, 445 (7127), 519−522. (6) Stern, E.; Vacic, A.; Reed, M. A. IEEE Trans. Electron Devices 2008, 55 (11), 3119−3130. (7) Chiesa, M.; Cardenas, P. P.; Otón, F.; Martinez, J.; Mas-Torrent, M.; Garcia, F.; Alonso, J. C.; Rovira, C.; Garcia, R. Nano Lett. 2012, 12 (3), 1275−1281. (8) Duan, X. X.; Li, Y.; Rajan, N. K.; Routenberg, D. A.; Modis, Y.; Reed, M. A. Nat. Nanotechnol 2012, 7 (6), 401−407. (9) Gao, A.; Lu, N.; Wang, Y.; Dai, P.; Li, T.; Gao, X.; Wang, Y.; Fan, C. Nano Lett. 2012, 12 (10), 5262−5268. (10) Shen, F.; Wang, J.; Xu, Z.; Wu, Y.; Chen, Q.; Li, X.; Jie, X.; Li, L.; Yao, M.; Guo, X.; Zhu, T. Nano Lett. 2012, 12 (7), 3722−3730. (11) Chen, S.; Bomer, J. G.; Carlen, E. T.; van den Berg, A. Nano Lett. 2011, 11 (6), 2334−2341. (12) Clement, N.; Nishiguchi, K.; Dufreche, J. F.; Guerin, D.; Fujiwara, A.; Vuillaume, D. Appl. Phys. Lett. 2011, 98, 014104. (13) Rajan, N. K.; Duan, X.; Reed, M. A. Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol. 2013, 5 (6), 629−645. E


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(14) Wei, C. Q.; Xiong, Y. Z.; Zhou, X. IEEE Trans. Electron Devices 2009, 56 (11), 2800−2810. (15) Li, J.; Vitusevich, S. A.; Petrychuk, M. V.; Pud, S.; Offenhäusser, A.; Danilchenko, B. A. J. Appl. Phys. 2013, 114 (20), 203704. (16) Rajan, N. K.; Routenberg, D. A.; Chen, J.; Reed, M. A. IEEE Electron Device Lett. 2010, 31 (6), 615−617. (17) Zheng, G. F.; Gao, X. P. A.; Lieber, C. M. Nano Lett. 2010, 10 (8), 3179−3183. (18) Pud, S.; Li, J.; Sibiliev, V.; Petrychuk, M.; Kovalenko, V.; Offenhäusser, A.; Vitusevich, S. Nano Lett. 2014, 14, 578−584. (19) Tarasov, A.; Fu, W.; Knopfmacher, O.; Brunner, J.; Calame, M.; Schonenberger, C. Appl. Phys. Lett. 2011, 98, 012114. (20) Knopfmacher, O.; Tarasov, A.; Fu, W.; Wipf, M.; Niesen, B.; Calame, M.; Schonenberger, C. Nano Lett. 2010, 10 (6), 2268−74. (21) Rajan, N. K.; Routenberg, D. A.; Reed, M. A. Appl. Phys. Lett. 2011, 98 (26), 264107. (22) Gao, X. P. A.; Zheng, G.; Lieber, C. M. Nano Lett. 2009, 10 (2), 547−552. (23) Vandamme, L. K. J.; Hooge, F. N. IEEE Trans. Electron Devices 2008, 55 (11), 3070−3085. (24) Vandamme, E. P.; Vandamme, L. K. J. IEEE Trans. Electron Devices 2000, 47 (11), 2146−2152. (25) Hung, K. K.; Ko, P. K.; Hu, C. M.; Cheng, Y. C. IEEE Trans. Electron Devices 1990, 37 (3), 654−665. (26) Clement, N.; Nishiguchi, K.; Fujiwara, A.; Vuillaume, D. Nat. Commun. 2010, 1, 92. (27) Kirton, M. J.; Uren, M. J. Adv. Phys. 1989, 38 (4), 367−468. (28) Clement, N.; Nishiguchi, K.; Fujiwara, A.; Vuillaume, D. IEEE Trans. Nanotechnol. 2011, 10 (5), 1172−1179. (29) Lukyanchikova, N. B.; Petrichuk, M. V.; Garbar, N. P.; Simoen, E.; Claeys, C. Microelectron. Eng. 1999, 48 (1−4), 185−188. (30) Vandamme, L. K. J.; Sodini, D.; Gingl, Z. Solid-State Electron. 1998, 42 (6), 901−905. (31) Martin-Gonthier, P.; Magnan, P. IEEE Electron Device Lett. 2011, 32 (6), 776−778. (32) Zanolla, N.; Siprak, D.; Tiebout, M.; Baumgartner, P.; Sangiorgi, E.; Fiegna, C. IEEE Trans. Electron Device 2010, 57 (5), 1119−1128. (33) Bolt, G. H. J. Phys. Chem. 1957, 61 (9), 1166−1169. (34) Hall, R. N. Phys. Rev. 1952, 87 (2), 387−387. (35) Shockley, W.; Read, W. T. Phys. Rev. 1952, 87 (5), 835−842. (36) Yuzhelevski, Y.; Yuzhelevski, M.; Jung, G. Rev. Sci. Instrum. 2000, 71 (4), 1681−1688. (37) Schulz, M. J. Appl. Phys. 1993, 74 (4), 2649−2657. (38) Mueller, H. H.; Worle, D.; Schulz, M. J. Appl. Phys. 1994, 75 (6), 2970−2979. (39) Mueller, H. H.; Worle, D.; Schulz, M. Microelectron. Eng. 1993, 22 (1−4), 181−184. (40) Lukyanchikova, N. B.; Petrichuk, M. V.; Garbar, N. P.; Simoen, E.; Claeys, C. Appl. Phys. Lett. 1998, 73. (41) Zhuge, J.; Zhang, L. L.; Wang, R. S.; Huang, R.; Kim, D. W.; Park, D.; Wang, Y. Y. Appl. Phys. Lett. 2009, 94, 083503.

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Sensitivity Enhancement of Si Nanowire Field Effect Transistor

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