Volt-current characteristics for tunneling through insulating films

We compare the charge transport characteristics of heavy doped p ++ -and n ++ -Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p ++ -and n ++ -type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current.

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“…34,35 In regions a and c, the bias acts to reduce the averaged tunneling barrier by ∼ |V |/2. With a moderate negative voltage to the metal (Fig.…”

Section: Resultsmentioning

confidence: 99%

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Yaffe

Scheres

et al. 2012

Phys. Rev. B

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“…Processes such as tunneling or ballistic transport are non-activated and, therefore, temperature-independent. [170][171][172][173] Remarkably, for majority carrier p-Si MOMS junctions (Fig. 7a, p-SiÀC 18 /Hg) only ''metal-like'' behavior is found.…”

Section: Quasi-metallic Temperature Behavior For Monolayer-limited Cumentioning

confidence: 99%

Molecules on Si: Electronics with Chemistry

et al. 2009

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Basic scientific interest in using a semiconducting electrode in molecule‐based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test‐bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor‐molecule electronics we need reproducible, high‐yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power.To consider these issues and questions we will, in this Progress Report, review junctions based on direct bonding of molecules to oxide‐free Si. describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified. investigate to what extent imperfections in the monolayer are important for transport across the monolayer. revisit the concept of energy levels in such hybrid systems.

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“…For this purpose, we adapted expressions from Stratton. 50,51 Note that the complete conductivity model comprises of merely three fit parameters. The conductivity model and, in particular, the electron tunneling at grain boundaries will be described in more detail elsewhere.…”

Section: B Seed Layer: Temperature Variationmentioning

confidence: 99%

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

Sommer

Stanley

Köhler

et al. 2015

Journal of Applied Physics

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This work elucidates the effect of the dopant aluminum on the growth of magnetron-sputtered aluminum-doped zinc oxide (ZnO:Al) films by means of a seed layer concept. Thin (<100 nm), highly doped seed layers and subsequently grown thick (∼800 nm), lowly doped bulk films were deposited using a ZnO:Al2O3 target with 2 wt. % and 1 wt. % Al2O3, respectively. We investigated the effect of bulk and seed layer deposition temperature as well as seed layer thickness on electrical, optical, and structural properties of ZnO:Al films. A reduction of deposition temperature by 100 °C was achieved without deteriorating conductivity, transparency, and etching morphology which renders these low-temperature films applicable as light-scattering front contact for thin-film silicon solar cells. Lowly doped bulk layers on highly doped seed layers showed smaller grains and lower surface roughness than their counterpart without seed layer. We attributed this observation to the beneficial role of the dopant aluminum that induces an enhanced surface diffusion length via a surfactant effect. The enhanced surface diffusion length promotes 2D-growth of the highly doped seed layer, which is then adopted by the subsequently grown and lowly doped bulk layer. Furthermore, we explained the seed layer induced increase of tensile stress on the basis of the grain boundary relaxation model. The model relates the grain size reduction to the tensile stress increase within the ZnO:Al films. Finally, temperature-dependent conductivity measurements, optical fits, and etching characteristics revealed that seed layers reduced grain boundary scattering. Thus, seed layers induced optimized grain boundary morphology with the result of a higher charge carrier mobility and more suitable etching characteristics. It is particularly compelling that we observed smaller grains to correlate with an enhanced charge carrier mobility. A seed layer thickness of 5 nm was sufficient to induce the beneficial effects.

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Volt-current characteristics for tunneling through insulating films

Cited by 466 publications

References 9 publications

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Molecules on Si: Electronics with Chemistry

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

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