Field Emission at Grain Boundaries: Modeling the Conductivity in Highly Doped Polycrystalline Semiconductors

Sommer, Nicolas; Hüpkes, J.; Rau, Uwe

doi:10.1103/physrevapplied.5.024009

Cited by 28 publications

(13 citation statements)

References 87 publications

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“…This is also consistent with reports on other degenerately doped polycrystalline systems, where the main conduction mechanism to surpass grain boundaries is a tunneling mechanism. These are, for example, Al‐doped ZnO or In‐doped CdS, where field‐emission as predominant tunneling mechanism has been identified and thermionic emission over the barriers (e.g., grain boundary scattering as given in Equations and ) could have been mostly neglected due to too high barrier heights and low barrier widths.…”

Section: Resultsmentioning

confidence: 99%

Suppression of Grain Boundary Scattering in Multifunctional p‐Type Transparent γ‐CuI Thin Films due to Interface Tunneling Currents

Kneiß

Yang

Barzola‐Quiquia

et al. 2018

Adv Materials Inter

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Transparent p‐type conductive γ‐CuI thin films typically exhibit unexpectedly high hole mobilities in the range of 10 cm2 V−1 s−1 even when heavily textured. To explain this phenomenon, the transport properties of such thin films are investigated. The temperature‐dependent resistivities of the textured (111)‐oriented films with different carrier concentration are fitted using the fluctuation‐induced tunneling conductivity (FITC) model in series with a power law. The FITC model describes barriers at the grain boundaries whereas the power law considers the scattering in the metallic interior of the grains. Magnetoresistance measurements performed on a reactively DC‐sputtered thin film at low temperatures (T < 8 K) suggest a 2D weak antilocalization effect with phase coherence lengths of about 50 nm. This is corroborated by a typical logarithmic temperature dependence of the zero‐field conductance. An n‐type inversion layer or a defect band at the interfaces of the grains as origin of the 2D carrier system and the barriers at the grain boundaries is proposed. This leads to a conclusive description of the electrical transport properties of γ‐CuI thin films and explains the high hole mobilities which are due to a suppressed backscattering at the grain boundaries in the presence of tunneling channels.

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Section: Resultsmentioning

confidence: 99%

Suppression of Grain Boundary Scattering in Multifunctional p‐Type Transparent γ‐CuI Thin Films due to Interface Tunneling Currents

Kneiß

Yang

Barzola‐Quiquia

et al. 2018

Adv Materials Inter

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“…Other scattering mechanisms in degenerate ZnO, such as optical and acoustical phonon scattering, piezoelectric scattering, dislocation scattering, and neutral impurity scattering, are less significant, but not negligible. They were described in detail by other authors and their individual contributions can be distinguished by temperature dependency analyses, although it is not easy.…”

Section: Transport Processes In Znomentioning

confidence: 99%

“…The barrier height derived by Seto is measured relative to the conduction‐band minimum. According to Schottky's theory, the barrier height is given with respect to the Fermi level …”

Section: Transport Processes In Znomentioning

confidence: 99%

Possibilities of Increasing the Usability of Sputtered AZO Films as a Transparent Electrode

Novák

2019

Physica Status Solidi (a)

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Aluminum-doped zinc oxide (AZO) is a suitable material for use as transparent electrode. Due to its lower price it is applied in the production of silicon solar cells. However, it is difficult to obtain suitable electrical properties at low deposition temperatures. Moreover, the AZO films with low thickness exhibit significantly higher average resistivity, which limits their usability, especially if they are prepared on flexible substrates. A lot of effort is invested to replace indium tin oxide (ITO) to a much greater extent now, since Indium is rare and its price is rising, thus the preparation of lowthickness AZO films at low temperature is also subject of intense research. The presented paper summarizes the reported results, discusses the causes of the differences between ITO and AZO films, and suggests the direction of research and the potential solution that should lead to increased usability of AZO films and also possible replacement of ITO films.

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“…The conductivity model and, in particular, the electron tunneling at grain boundaries will be described in more detail elsewhere. 52 The seed layer sample showed a decreasing conductivity with raising temperature. This temperature dependence is characteristic for electron-phonon scattering.…”

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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Field Emission at Grain Boundaries: Modeling the Conductivity in Highly Doped Polycrystalline Semiconductors

Cited by 28 publications

References 87 publications

Suppression of Grain Boundary Scattering in Multifunctional p‐Type Transparent γ‐CuI Thin Films due to Interface Tunneling Currents

Suppression of Grain Boundary Scattering in Multifunctional p‐Type Transparent γ‐CuI Thin Films due to Interface Tunneling Currents

Possibilities of Increasing the Usability of Sputtered AZO Films as a Transparent Electrode

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

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