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Register a new userPercolation description of charge transport in amorphous oxide semiconductors
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The charge transport mechanism in amorphous oxide semiconductors (AOS) is a matter of controversial debates. Most theoretical studies so far neglected the percolation nature of the phenomenon. In this article, a recipe for theoretical description of charge transport in AOSs is formulated using the percolation arguments. Comparison with the previous theoretical studies shows a superiority of the percolation approach. The results of the percolation theory are compared to experimental data obtained in various InGaZnO materials revealing parameters of the disorder potential in such AOS.
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Charge transport in amorphous oxide semiconductors is often described as the band transport affected by disorder in the form of random potential barriers (RB). Theoretical studies in the framework of this approach neglected so far the percolation nature of the phenomenon. In this article, a recipe for theoretical description of charge transport in the RB model is formulated using percolation arguments. Comparison with the results published so far evidences the superiority of the percolation approach.
We study charge transport in a monolayer molybdenum disulfide nanoflake over a wide range of carrier density, temperature, and electric bias. We find that the transport is best described by a percolating picture in which the disorder breaks translational invariance, breaking the system up into a series of puddles, rather than previous pictures in which the disorder is treated as homogeneous and uniform. Our work provides insight to a unified picture of charge transport in monolayer molybdenum disulfide nanoflakes and contributes to the development of next-generation molybdenum disulfide based devices.
The potential of semiconductors assembled from nanocrystals (NC semiconductors) has been demonstrated for a broad array of electronic and optoelectronic devices, including transistors, light emitting diodes, solar cells, photodetectors, thermoelectrics, and phase charge memory cells. Despite the commercial success of nanocrystals as optical absorbers and emitters, applications involving charge transport through NC semiconductors have eluded exploitation due to the inability for predictive control of their electronic properties. Here, we perform large-scale, ab-initio simulations to understand carrier transport, generation, and trapping in NC-based semiconductors from first principles. We use these findings to build the first predictive model for charge transport in NC semiconductors, which we validate experimentally. Our work reveals that we have been thinking about transport in NC semiconductors incorrectly. Our new insights provide a path for systematic engineering of NC semiconductors, which in fact offer previously unexplored opportunities for tunability not achievable in other semiconductor systems.
Recently amorphous oxide semiconductors (AOS) have gained commercial interest due to their low-temperature processability, high mobility and areal uniformity for display backplanes and other large area applications. A multi-cation amorphous oxide (a-IGZO) has been researched extensively and is now being used in commercial applications. It is proposed in the literature that overlapping In-5s orbitals form the conduction path and the carrier mobility is limited due to the presence of multiple cations which create a potential barrier for the electronic transport in a-IGZO semiconductors. A multi-anion approach towards amorphous semiconductors has been suggested to overcome this limitation and has been shown to achieve hall mobilities up to an order of magnitude higher compared to multi-cation amorphous semiconductors. In the present work, we compare the electronic structure and electronic transport in a multi-cation amorphous semiconductor, a-IGZO and a multi-anion amorphous semiconductor, a-ZnON using computational methods. Our results show that in a-IGZO, the carrier transport path is through the overlap of outer s-orbitals of mixed cations and in a-ZnON, the transport path is formed by the overlap of Zn-4s orbitals, which is the only type of metal cation present. We also show that for multi-component ionic amorphous semiconductors, electron transport can be explained in terms of orbital overlap integral which can be calculated from structural information and has a direct correlation with the carrier effective mass which is calculated using computationally expensive first principle DFT methods.
We discuss memory effects in the conductance of hopping insulators due to slow rearrangements of structural defects leading to formation of polarons close to the electron hopping states. An abrupt change in the gate voltage and corresponding shift of the chemical potential change populations of the hopping sites, which then slowly relax due to rearrangements of structural defects. As a result, the density of hopping states becomes time dependent on a scale relevant to rearrangement of the structural defects leading to the excess time dependent conductivity.
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