It is well known that metal/Tin-dioxide/metal sandwich structures exhibit a field-assisted lowering of the potential barrier between donor-like center and the conduction band edge, known as the Poole-Frenkel effect. This behavior is indicated by a linear dependence of Iog  on 1/2, where  is the current density, and  is the applied voltage. In this study, the electrical properties of Cu/nano-SnO2/Cu sandwich structures were investigated through current-voltage measurements at room temperature. Also, an attempt to explore the governing current flow mechanism was tried. Our results indicate that noticeable feature appearing clearly in the current-voltage characterization is the Poole-Frenkel and space-charge-limited conduction mechanisms

Ali Hassanzadeh

Hassan Sedghi

Hossein Mahmoudi Chenari

Mir Maqsoud Golzan

Mohammad Talebian

Journal of Nanomaterials

It is well known that metal/Tin-dioxide/metal sandwich structures exhibit a field-assisted lowering of the potential barrier between donor-like center and the conduction band edge, known as the Poole-Frenkel effect. This behavior is indicated by a linear dependence of Iog  on , where is the current density, and is the applied voltage. In this study, the electrical properties of Cu/nano-SnO2/Cu sandwich structures were investigated through current-voltage measurements at room temperature. Also, an attempt to explore the governing current flow mechanism was tried. Our results indicate that noticeable feature appearing clearly in the current-voltage characterization is the Poole-Frenkel and space-charge-limited conduction mechanisms.</jats:p

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Hindawi Publishing CorporationJournal of NanomaterialsVolume 2011, Article ID 190391, 4 pagesdoi:10.1155/2011/190391Research ArticlePoole-Frenkel Conduction in Cu/Nano-SnO2/Cu ArrangementHossein Mahmoudi Chenari,1 Hassan Sedghi,2 Mohammad Talebian,2Mir Maqsoud Golzan,2 and Ali Hassanzadeh31 Department of Physics, Faculty of Science, Maraghe University, Maraghe, Iran2 Department of Physics, Faculty of Science, Urmia University, Urmia, Iran3 Department of Chemistry, Faculty of Science, Urmia University, Urmia, IranCorrespondence should be addressed to Hossein Mahmoudi Chenari, hmahmodiph@yahoo.comReceived 31 December 2010; Revised 6 May 2011; Accepted 23 May 2011Academic Editor: Shaogang HaoCopyright © 2011 Hossein Mahmoudi Chenari et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.It is well known that metal/Tin-dioxide/metal sandwich structures exhibit a field-assisted lowering of the potential barrier betweendonor-like center and the conduction band edge, known as the Poole-Frenkel eﬀect. This behavior is indicated by a lineardependence of Iog J on V 1/2, where J is the current density, and V is the applied voltage. In this study, the electrical propertiesof Cu/nano-SnO2/Cu sandwich structures were investigated through current-voltage measurements at room temperature. Also,an attempt to explore the governing current flow mechanism was tried. Our results indicate that noticeable feature appearingclearly in the current-voltage characterization is the Poole-Frenkel and space-charge-limited conduction mechanisms.1. IntroductionNanocrystalline materials with average grain size of less than50 nm have attracted considerable scientific interest becauseof their unusual physical and chemical properties [1]. Themicrostructure of nanocrystalline materials depends uponthe method of preparation. Tin dioxide (SnO2), a wideband gap (3.6 eV) n-type semiconductor, is one of the mostimportant materials for gas sensors [2]. It is well known forits application in gas sensors and dye-based solar cells [3].Because of their relatively low operating temperature andas oxidizing gases, SnO2 nanoparticles have been extremelystudied [4]. As a transparent conducting oxide (TCO), it hasbeen widely used as optoelectronic devices such as flat paneldisplays and thin film solar energy cells [5]. As an n-typesemiconductor, tin dioxide has been actively explored as thefunctional component in detecting combustible gases such asCO, H2, and CH4 [6]. Most of these studies concentrated ondevices, which were fabricated with polycrystalline films asthe sensing units [7]. Nanostructures of SnO2 could also beemployed to detect various gases [8, 9].In some of these applications, the mechanism of elec-tronic conduction strongly aﬀects the device characteristics.Therefore, one needs to understand conduction mechanism.The type of electronic conduction mechanism depends onseveral factors, in particular, the nature of the metalliccontact to the semiconductor (either ohmic or blocking), thelevel of voltage applied across the sample, surface roughness,and grain size and its temperature. Metal-semiconductor(MS) structures (or Schottky diodes) have been studiedextensively because of the very importance and critical com-ponents in integrated circuit technology. Moreover, it is avery attractive tool for the characterization of semiconductormaterials [10–13].In the present work, We examine the mechanisms, whichcontrol carrier transport in Cu/nano-SnO2/Cu sandwichstructures. These include the study of gate voltage depen-dence of device leakage current.2. Experimental DetailsSnO2 nanoparticles were synthesized by a simple sol-gelmethod which its details reported elsewhere [14]. SnO2nanopowder Pellets were made by applying a uniaxialpressure of 312.92 atmospheres on the powder sample.Polarizationmeasurements were performed on the Cu/nano-SnO2/Cu sequence system using a computer-controlledAUTOLAB potentiostat and galvanostat.2 Journal of Nanomaterials−3 −2 −1 0 1 2 3−9−8−7−6−5−4−3−217.2 nm52.4 nmV (Volt)log|J|(Acm2)Figure 1: log |J| versus V characteristic of nano-SnO2 withdiﬀerent grain sizes.3. Results and Discussion3.1. Polarization Study. A typical forward bias semiloga-rithmic log |J| versus V characteristic of Cu/nano-SnO2/Cusandwich structures is shown in Figure 1. The leakagecurrent can be aﬀected by the surface roughness andgrain size. The smaller grain size produces more grainboundaries and causes more leakage current [15]. Hence,it is suggested that the decrease of the leakage currentof specimens can be attributed to the reduction of thesurface roughness. The log |J|-V characteristics show alsono double blocking behavior (see Figure 1). We assume thatthe copper electrode as a back contact does not block thecurrent in reverse direction, which is especially the casefor very low barriers. So the current transport throughthe Cu contact dominates the log |J|-V characteristic forpositive voltages. Schottky emission, Poole-Frenkel, space-charge-limited conduction (SCLC), and so forth, are thepossible conduction mechanisms in the studied junctions[16]. The governing conduction mechanism in Cu/nano-SnO2/Cu Schottky diodes at hand can be figured out from thepower of log |J|-V curve. Power of the curve greater than2 (m > 2) indicates SCLC mechanism whereas being equalto 1 (m = 1) imply ohmic character. When the power liesbetween 1 and 2 imposing either Schottky or Poole-Frenkelconduction mechanism. The linear sections of the curvecould be interpreted in terms of either the Schottky emissionor Poole-Frenkel emission. For the Schottky emission, thecurrent density J is expressed as follows [17]:J = A∗T2 exp(−ϕkT)exp(eβsV1/2/kTd1/2), (1)where A∗ is the eﬀective Richardson constant, ϕ is theSchottky barrier height at the electrode contact, and βs is theSchottky field lowering constant. For Pool-Frenkel emission,the current density is given byJ = Jpf0exp(βpfV 1/2q/kTd1/2), (2)1.2 1.4 1.6 1.8 2−7−6.8−6.6−6.4−6.2−6y = 1.2x − 8.6y = 2.7x − 11y = 0.8x − 7.617.6 nmV (Voltage)abcdlog|J|Figure 2: Forward bias log |J|-V plot of the Cu/nano-SnO2/Cuarrangement with a grain size of 17.6 nm.where βpf is the Pool-Frenkel coeﬃcient. The theoreticalvalues of these coeﬃcients are given by2βs = βpf =(eπεε0)1/2. (3)For Schottky diodes, thermionic emission (TE) modelsuggests the following J-V relationship:J = J0 exp(eV/nκT), (4)where V , κ,T ,n and J0 are the applied voltage, Boltzmanconstant, temperature, ideality factor, and saturation currentdensity, respectively. The saturation current density is givenbyJ0 = A∗T2exp(−eϕb/κT), (5)where A∗, ϕb, and e are the Richardson constant, barrierheight, and electron charge, respectively. The parametersJ0 and ϕb for SnO2 nanoparticles with a grain size of17.6 nm were calculated 8.6472 × 10−4 A and 0.6015 eV,and for SnO2 nanoparticles with a grain size of 52.4 nmwere obtained 0.0312 A and 0.5073 eV, respectively, using theabove equations.As shown in Figure 2, three linear regions are eventualin the log |J|-V characteristic of the Cu/nano-SnO2/Cusandwich structure. One of them is in the lower-voltageregion (1.2 < V < 1.6), where the power is equal to1.2, imposing either Schottky or Poole-Frenkel conductionmechanism. In the second region, with increasing voltage,more electrons injected from electrode into the film andcurrent density originates from the SCLC mechanism, wherethe power is equal to 2.7. Abrupt increment of the currentdensity is characteristic of the SCLC mechanism due tothe trapped carriers. As the applied voltage is increasedfurther, strong injection of electrons takes place and causesan increase in the density of filled trapping sites and leadingto an increase of film conduction. An abrupt increase inleakage current appeared which follows a trap-filled limitedlaw. For this conduction, the increasing slop indicates thatthe I-V correlations are determined by another distributedtrap type [18].In the higher voltage region (Section 3), less slope isobservable and the “quasisaturation” of the current may beJournal of Nanomaterials 30.1 0.2 0.3 0.4 0.5 0.6−4−3.8−3.6−3.4−3.2−3d = 52.4 nmy = 3.2x − 4.1y = 1.16x − 3.7V (Volt)abclog|J|(Acm2)Figure 3: Forward bias log |J|-V plot of the Cu/nano-SnO2/Cuarrangement with a grain size of 52.4 nm.−7.1−7−6.9−6.8−6.7−6.61.12 1.14 1.16 1.18 1.2 1.22 1.24 1.2617.6 nmlog|J|(Acm2)V1/2 (Volt)Figure 4: Log J-V 1/2 plot of the Cu/nano-SnO2/Cu arrangementwith a grain size of 17.6 nm.caused by the charge trapping. Consequently, an internalelectric field is created, which is opposed to the externalelectric field, limiting the carriers flow. As can be seen inthe Figure 3, similar analysis is carried out for nanostructureSnO2 with a grain size of 52.4 nm.The other possibility for the nonlinear J-V charac-teristics is bulk-limited Poole-Frenkel emission. Figure 4shows the plot of ln |J| versus V 1/2 for Cu/nano-SnO2/Cuarrangement with a grain size of 17.6 nm, which clearlyyields a linear section of the curve, could be interpreted interms of either Schottky emission or Pool-Frenkel emission.Corresponding experimental value of β calculated fromthe slope of the linear region of Figure 4 was found tobe 3.63 × 10−5 eVm1/2 V−1/2. The experimental value ofβ for SnO2 nanoparticles with a grain size of 52.4 nm,derived from the slope of the linear section of Figure 5, wasfound to be 3.42×10−5 eVm1/2 V−1/2. Theoretical values ofβs and βpf were found to be 1.88 × 10−5 eVm1/2 V−1/2 and3.76 × 10−5 eVm1/2 V−1/2, respectively. Experimental valuefor β in the both nanoparticle is nearly agreement with thetheoretically calculated value of βpf. Hence, we can concludethat the conductionmechanism in our nanocrystalline film iscontroled by the Poole-Frenkel eﬀect and the Schottky eﬀectis probably masked by the Poole-Frenkel emission from some−4.4−4.3−4.2−4.1−4−3.9−3.8−3.7−3.60.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.3852.4 nmlog|J|(Acm2)V1/2 (Volt)Figure 5: Log J-V 1/2 plot of the Cu/nano-SnO2/Cu arrangementwith a grain size of 52.4 nm.shallow traps at grain boundaries. The adsorbed oxygenatoms at the grain boundary produce defect states which trapcarriers and create a potential barrier. By applying an appliedfield, the barrier height is diminished and electrons can flowfrom interfacial states, thus it can be reason of the existenceof the Poole-Frenkel mechanism [19].4. ConclusionThe tetragonal tin dioxide nanoparticles were obtained byusing sol-gel technique with thermal treatments. Possiblemechanism for leakage current conduction in the Cu/nano-SnO2/Cu sequence system showed characteristics of typicalSchottky-barrier devices. The Poole-Frenkel eﬀect has beenobserved in nanotin oxide thick film. This eﬀect depends onthe electron transport phenomenon through grain bound-aries. Nanostructured SnO2 films with a large number ofgrain boundaries contain a considerable number of trapstates.References[1] H. Gleiter, “Nanocrystalline materials,” Progress in MaterialsScience, vol. 33, no. 4, pp. 223–315, 1989.[2] M. R. Yang, S. Y. Chu, and R. C. Chang, “Synthesis and studyof the SnO2 nanowires growth,” Sensors and Actuators, B, vol.122, no. 1, pp. 269–273, 2007.[3] S. Ferrere, A. Zaban, and B. A. Gregg, “Dye sensitization ofnanocrystalline tin oxide by perylene derivatives,” Journal ofPhysical Chemistry B, vol. 101, no. 23, pp. 4490–4493, 1997.[4] A. R. Babar, S. S. Shinde, A. V. Moholkar, and K.Y. Rajpure, “Electrical and dielectric properties of co-precipitated nanocrystalline tin oxide,” Journal of Alloys andCompounds, vol. 505, no. 2, pp. 743–749, 2010.[5] N. Amin, T. Isaka, A. Yamada, and M. Konagai, “Highlyeﬃcient 1 μm thick CdTe solar cells with textured TCOs,” SolarEnergy Materials and Solar Cells, vol. 67, no. 1–4, pp. 195–201,2001.[6] J. Kappler, A. Tomescu, N. Barsan, and V. Weimar, “COconsumption of Pd doped SnO2 based sensors,” Thin SolidFilms, vol. 391, no. 2, pp. 186–191, 2001.4 Journal of Nanomaterials[7] R. Scott, S. Yang, D. Williams, and G. Ozin, “Electronicallyaddressable SnO2 inverted opal gas sensors fabricated on inter-digitated gold microelectrodes,” Chemical Communications,no. 6, pp. 688–689, 2003.[8] A. Kolmakov, Y. Zhang, G. Cheng, and M. Moskovits,“Detection of CO and O2 using tin oxide nanowire sensors,”Advanced Materials, vol. 15, no. 12, pp. 997–1000, 2003.[9] A. Maiti, J. A. Rodriguez, M. Law, P. Kung, J. R. Mckinney, andP. Yang, “SnO2 nanoribbons as NO2 sensors: insights from firstprinciples calculations,” Nano Letters, vol. 3, no. 8, pp. 1025–1028, 2003.[10] M. A. Cowley and M. S. Sze, “Surface states and barrier heightof metal-semiconductor systems,” Journal of Applied Physics,vol. 36, no. 10, pp. 3212–3220, 1965.[11] M. O. Nielsen, “Influence of semiconductor barrier tunnelingon the current-voltage characteristics of tunnel metal-oxide-semiconductor diodes,” Journal of Applied Physics, vol. 54, no.10, pp. 5880–5886, 1983.[12] C. H. Card and H. E. Rhoderick, “Studies of tunnel MOSdiodes I. Interface eﬀects in silicon Schottky diodes,” Journalof Physics D, vol. 4, no. 10, pp. 1589–1601, 1971.[13] A. Tataroglu and X. S. Altındal, “Characterization of current-voltage (I-V) and capacitance-voltage-frequency (C-V-f) fea-tures of Al/SiO2/p-Si (MIS) Schottky diodes,” MicroelectronicEngineering, vol. 83, no. 3, pp. 582–588, 2006.[14] A. Hassanzadeh, B. Moazzez, H. Haghgooie, M. Nasseri, M.M. Golzan, and H. Sedghi, “Synthesis of SnO2 nanopowdersby a sol-gel process using propanol-isopropanol mixture,” TheCentral European Journal of Chemistry, vol. 6, no. 4, pp. 651–656, 2008.[15] M. S. Tsai, S. C. Sun, and T. Y. Tseng, “Eﬀect of oxygen toargon ratio on properties of (Ba,Sr)TiO3 thin films preparedby radio-frequency magnetron sputtering,” Journal of AppliedPhysics, vol. 82, no. 7, p. 3428, 1997.[16] M. S. Sze and K. K. Ng, Physics of Semiconductor Devices, JohnWiley & Sons, Hoboken, NJ, USA, 2007.[17] A. Wilson and R. A. Collins, “Electrical characteristics ofplanar phthalocyanine thin film gas sensors,” Sensors andActuators, vol. 12, no. 4, pp. 389–403, 1987.[18] L. Zhang, J. Zhai, W. Mo, and X. Yao, “The dielectric andleakage current behavior of CoFe2O4-BaTiO3 composite filmsprepared by combining method of sol-gel and electrophoreticdeposition,” Solid State Sciences, vol. 12, no. 4, pp. 509–514,2010.[19] A. N. Banerjee, R. Maity, S. Kundoo, and K. K. Chattopadhyay,“Poole-Frenkel eﬀect in nanocrystalline SnO2:F thin filmsprepared by a sol-gel dip-coating technique,” Physica StatusSolidi A, vol. 201, no. 5, pp. 983–989, 2004.Submit your manuscripts athttp://www.hindawi.comScientificaHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014CorrosionInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Polymer ScienceInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014CeramicsJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014CompositesJournal ofNanoparticlesJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014International Journal ofBiomaterialsHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014NanoscienceJournal ofTextilesHindawi Publishing Corporation http://www.hindawi.com Volume 2014Journal ofNanotechnologyHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Journal ofCrystallographyJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014CoatingsJournal ofAdvances in Materials Science and EngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014 Smart Materials ResearchHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014MetallurgyJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014BioMed Research InternationalMaterialsJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014NanomaterialsHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Journal ofNanomaterials

Poole-Frenkel Conduction in Cu/Nano-SnO 2

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