Energy-dependent relaxation time in quaternary amorphous oxide semiconductors probed by gated Hall effect measurements

Socratous, Josephine; Watanabe, Shun; Banger, Kulbinder K.; Warwick, Christopher; Branquinho, Rita; Barquinha, Pedro; Martins, Rodrigo; Fortunato, Elvira; Sirringhaus, Henning

doi:10.1103/physrevb.95.045208

Cited by 10 publications

(5 citation statements)

References 20 publications

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“…This is similar in value to that reported by Wager et al. for ZTO TFTs and to those of amorphous indium gallium zinc oxide TFTs reported by many groups and that are commercially very significant for the display industry. In these TFTs, under most conditions, the mean free path is larger than the equivalent lattice constant in this amorphous semiconductor, which is about 0.5 nm.…”

Section: Resultssupporting

confidence: 90%

Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

Wang

Dodabalapur

2018

Annalen der Physik

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The multiple trap and release (MTR) model is extended to more completely and accurately describe charge transport in high-mobility amorphous metal oxide thin-film transistors (TFTs). In addition to trapping and release of charges, other scattering mechanisms that influence mobility are considered along with screening by free carriers. The mobility for each of the dominant scattering mechanisms is calculated using the Boltzmann transport equation (BTE) in the relaxation time approximation. It is found that trapped carriers very effectively scatter the charges that move in extended states. This type of scattering is unique to TFTs. Experimental data from high-mobility amorphous metal oxide TFTs are compared with calculations with very good agreement. At high temperatures, scattering by longitudinal optical phonons and surface phonons becomes significant. This work represents the first successful combination of charge carrier scattering and the BTE with thermally activated MTR transport in a disordered semiconductor. Charge transport in amorphous metal oxide transistors is quantitatively described for the first time and the factors that influence the mobility at various temperatures and charge carrier densities are clearly described. This approach can be used for describing transport in several amorphous and polycrystalline semiconductors with significant disorder and trapping.

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Section: Resultssupporting

confidence: 90%

Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

Wang

Dodabalapur

2018

Annalen der Physik

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“…Both Spin-CS and PLD TFTs exhibit a downward trend in μ sat with increasing Ga content (Figure A). This trend has previously been reported in both TFT-derived mobility ,, and Hall mobility for a-IGO films grown by sputtering , and solution processing methodologies. , Recent work, using gated Hall-effect measurements, suggests Ga influences transport in a-oxide semiconductors . More specifically, molecular dynamics simulations combined with density functional theory illustrate that the preference of Ga to remain 4-fold coordinate is effective in disordering and disrupting the conduction manifold and thus decreases mobility. , Here, we expand this study by providing evidence, through extended X-ray absorption fine structure (EXAFS) analysis (Figure ), that the 4-fold coordinate Ga mechanism is also present in CS films.…”

Section: Results and Discussionsupporting

confidence: 71%

“…15,45 Recent work, using gated Hall-effect measurements, suggests Ga influences transport in a-oxide semiconductors. 48 More specifically, molecular dynamics simulations combined with density functional theory illustrate that the preference of Ga to remain 4-fold coordinate is effective in disordering and disrupting the conduction manifold and thus decreases mobility. 27,49 Here, we expand this study by providing evidence, through extended X-ray absorption fine structure (EXAFS) analysis (Figure 4), that the 4-fold coordinate Ga mechanism is also present in CS films.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Processing, Structure, and Transistor Performance: Combustion versus Pulsed Laser Growth of Amorphous Oxides

Moffitt

Stallings

Falduto

et al. 2019

ACS Appl. Electron. Mater.

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Solution-phase growth of amorphous oxide semiconducting films will likely provide significant advances toward the realization of affordable, flexible, transparent electronics. However, solution processing methods are still under development, and the bulk of amorphous oxide studies investigate films grown via physical vapor deposition (PVD) methods. To leverage the existing knowledge base on amorphous oxides, this study directly compares one of the most promising solution processing techniques, combustion synthesis (CS; spin and spray methodologies), with a more established PVD growth technique, pulsed laser deposition (PLD). The roles of processing technique and composition are understood by coupling structural studies, including analysis of local bonding and density, with the existing literature of PVD amorphous oxide films. This work represents the first example of X-ray absorption spectroscopy analysis of spray combustion processing (Spray-CS) a-oxide films. Trends in film structure and transistor performance are compared in the amorphous In−Ga−O (a-IGO) system, across a broad In−Ga composition space, as calibrated by X-ray fluorescence. Semiconducting layers deposited by either CS or PLD are used as the channel layer in thin film transistors (TFTs) fabricated on SiO 2 /Si substrates. A drop in TFT saturation mobility, with increasing Ga content, for PLD and spin-coated combustion processing (Spin-CS) devices is understood to be the disruption of carrier mobility imposed by the disparate local structure around Ga, as opposed to around In. In contrast, saturation mobility for Spray-CS films is dominated by the processing method and cannot be tuned with composition. TFTs with PLD-derived channel layers exhibit the highest saturation mobility, 42 cm 2 V −1 s −1 (maximum), which may be linked to their high density. Similar to mobility trends, TFT on-voltage rises with Ga content for Spin-CS and PLD-derived channel layers. A rise in on voltage is associated with decreasing carrier concentration induced by the dilution of low-oxygen-coordinated In centers, the source of carriers. As with mobility, on-voltage for Spray-CS derived TFTs is not well tuned with composition but is consistently near zero. Local structure studies reveal that the Spray-CS growth technique results in high In−O coordination levels, which explains the low carrier concentrations and resultant on voltage behavior. This work investigates, for the first time, the structural phase stability of solution-processed oxides through in situ glancing incidence X-ray diffraction annealing studies. Thermal phase stability, which informs processing parameters and device stability, is shown to increase with Ga content for all films.

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“…Introduction of this factor is one of the main points of this article which allows us to create a proper theoretical framework with which to analyze transport in semiconductors with mobilities that fall between regimes for which hopping transport theories and band transport theories apply. Several such semiconductors have been reported in recent years including those that exhibit a normal Hall Effect, which is a strong indicator of delocalized transport [44,45]. The here-defined TRF is shown as a function of mean free path length for exemplary intermolecular distance/lattice constant values in Fig.…”

Section: Transport Reduction Factor (Trf)mentioning

confidence: 99%

Redefining the Mobility Edge in Thin-Film Transistors

Wang

Dodabalapur

2019

Phys. Rev. Applied

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In most thin-film transistors, the concept of mobility edge needs to be redefined so as to take into account important constraints. In this paper we describe how the mobility edge concept has to be reinterpreted when applied to thin-film transistors. Charge carriers can be significantly localized due to strong scattering, altering the model of band transport in extended states so that, effectively, only a fraction of carriers can actually move in the extended states, in accordance with a statistical distribution of free paths. It is necessary to explicitly consider this effect in applying conventional semiconductor transport theories based on solutions to the Boltzmann Transport Equation (BTE). We are then able to apply the BTE with appropriate scattering mechanisms and obtain results that agree well with experiment for the case of a polymer thinfilm transistor (TFT). This approach is very well suited to thin-film transistors based on polymer and organic semiconductors, and also many amorphous oxide semiconductors with room temperature mobilities in the range 1-20 cm 2 /(Vs).

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Energy-dependent relaxation time in quaternary amorphous oxide semiconductors probed by gated Hall effect measurements

Cited by 10 publications

References 20 publications

Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

Processing, Structure, and Transistor Performance: Combustion versus Pulsed Laser Growth of Amorphous Oxides

Redefining the Mobility Edge in Thin-Film Transistors

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