Experimental validation of the exponential localized states distribution in the variable range hopping mechanism in disordered silicon films

Pichon, Laurent; Rogel, Régis

doi:10.1063/1.3625944

Cited by 9 publications

(3 citation statements)

References 20 publications

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“…Even if the γ −1 value is not obvious, these results of our proposed bandgap shallow tail state model mean that γ −1 ∼ 3 nm is an appropriate value for the studied polycrystalline silicon NWs. Moreover, such a value has been recently reported for such N(E F ) behavior deduced from analysis of the field effect conductance of low-temperature ( 600 • C) N-channel polycrystalline silicon TFTs reporting experimental determination of shallow tail state distribution close to the conduction band [23]. In addition, these exponential states distributions are consistent with theoretical studies previously reported in the case of hydrogenated amorphous silicon [20,21].…”

Section: Resultssupporting

confidence: 90%

Variable range hopping conduction in N- and P-typein situdoped polycrystalline silicon nanowires

Pichon

Jacques

Rogel

et al. 2012

Semicond. Sci. Technol.

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Temperature dependence of electrical properties in N-and P-type in situ doped polycrystalline silicon nanowires synthesized by the sidewall spacer formation technique has been studied. Experimental analysis has been carried out for a temperature range from 200 K to 530 K on in situ doped polycrystalline silicon nanowires with doping level varying from 2 × 10 16 to 9 × 10 18 cm −3 . Results show that for N-and P-type doped samples the temperature dependence of the conductivity follows the 3D variable range hopping model due to hopping between localized electronic states near the Fermi level. The corresponding densities of states are determined following exponential (tail states) distributions associated to the statistical shift of the Fermi level.

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Section: Resultssupporting

confidence: 90%

Variable range hopping conduction in N- and P-typein situdoped polycrystalline silicon nanowires

Pichon

Jacques

Rogel

et al. 2012

Semicond. Sci. Technol.

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“…VRH is a common transport mechanism in disordered materials (see e.g. [13][14][15][16]) that have a substantial density of localized states close to the Fermi level, with spatially overlapping wavefunctions. For materials in which the density of states at the Fermi level is suppressed by Coulombic electron-electron interactions, VRH is expected to follow the Efros-Shklovskii [17,18] model-i.e.…”

Section: Introductionmentioning

confidence: 99%

Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping

Cheah

Gómez-Navarro

Jaurigue

et al. 2013

J. Phys.: Condens. Matter

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We report an analysis of low-temperature measurements of the conductance of partially disordered reduced graphene oxide, finding that the data follow a simple crossover scenario. At room temperature, the conductance is dominated by two-dimensional (2D) electric field-assisted, thermally driven (Pollak-Riess) variable-range hopping (VRH) through highly disordered regions. However, at lower temperatures T, we find a smooth crossover to follow the exp(-E0/E)(1/3) field-driven (Shklovskii) 2D VRH conductance behaviour when the electric field E exceeds a specific crossover value EC(T)(2D) = (EaE(1/3)0 /3)(3/4) determined by the scale factors E0 and Ea for the high-field and intermediate-field regimes respectively. Our crossover scenario also accounts well for experimental data reported by other authors for three-dimensional disordered carbon networks, suggesting wide applicability.

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“…VRH is a common transport mechanism in disordered materials [e.g. Pichon and Rogel 2011;Okada and Taniguchi 1997;Yosida and Oguro 1996;Hauser and Rodgers 1982] that have a substantial density of localized states close to the Fermi level, with spatially overlapping wavefunctions.…”

Section: Existing Variable-range Hopping Crossover Modelsmentioning

confidence: 99%

Electronic Conduction in Disordered Carbon Materials

Cheah¹

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<p>Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction.</p>

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Experimental validation of the exponential localized states distribution in the variable range hopping mechanism in disordered silicon films

Cited by 9 publications

References 20 publications

Variable range hopping conduction in N- and P-typein situdoped polycrystalline silicon nanowires

Variable range hopping conduction in N- and P-typein situdoped polycrystalline silicon nanowires

Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping

Electronic Conduction in Disordered Carbon Materials

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