Dependence Of Field-effect Mobility Research Articles

Experimental and modeling study of 1/f noise in multilayer MoS2 and MoSe2 field-effect transistors

In field-effect transistors (FETs) with two-dimensional (2D) transition metal dichalcogenide channels, the dependence of field-effect mobility on atomic layer thickness has been studied and interpreted in terms of interface scattering and interlayer coupling resistance (Rint). However, a model for 1/f noise, such as in MoS2 and in MoSe2 FETs, for various contact metals and layer number thicknesses has not been reported. In this work, we have experimentally studied current–voltage and 1/f noise on MoS2 and MoSe2 FETs with source and drain contacts of high and low work function metals to understand both the mobility and the noise behavior. We have developed a noise model incorporating layer number dependent Hooge parameters and Rint. The noise and mobility models utilize screening lengths for charge, mobility, and Hooge parameter to describe the variation of these quantities with a layer number. Using our single model topology with appropriate fitting parameters for each material and each contact metal, the model captures the experimentally observed layer thickness dependence of the Hooge parameter. Our noise analysis is fully comprehensive and, hence, could be applied to any 2D layered systems.

Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors

Polymer semiconductors provide unique possibilities and flexibility in tailoring their optoelectronic properties to match specific application demands. The recent development of semicrystalline polymers with strongly improved charge transport properties forces a review of the current understanding of the charge transport mechanisms and how they relate to the polymer's chemical and structural properties. Here, the charge density dependence of field effect mobility in semicrystalline polymer semiconductors is studied. A simultaneous increase in mobility and its charge density dependence, directly correlated to the increase in average crystallite size of the polymer film, is observed. Further evidence from charge accumulation spectroscopy shows that charges accumulate in the crystalline regions of the polymer film and that the increase in crystallite size affects the average electronic orbitals delocalization. These results clearly point to an effect that is not caused by energetic disorder. It is instead shown that the inclusion of short range coulomb repulsion between charge carriers on nanoscale crystalline domains allows describing the observed mobility dependence in agreement with the structural and optical characterization. The conclusions that are extracted extend beyond pure transistor characterization and can provide new insights into charge carrier transport for regimes and timescales that are relevant to other optoelectronic devices.

Temperature Dependence of Field-Effect Mobility in Organic Thin-Film Transistors: Similarity to Inorganic Transistors.

Carrier transport in solution-processed organic thin-film transistors (OTFTs) based on dioctylbenzothienobenzothiophene (C8-BTBT) has been investigated in a wide temperature range from 296 to 10 K. The field-effect mobility shows thermally activated behavior whose activation energy becomes smaller with decreasing temperature. The temperature dependence of field-effect mobility found in C8-BTBT is similar to that of others materials: organic semiconducting polymers, amorphous oxide semiconductors and hydrogenated amorphous silicon. These results indicate that hopping transport between isoenergetic localized states becomes dominated in a low temperature regime in these materials.

Kelvin probe force microscopy study on operating In-Sn-O-channel ferroelectric-gate thin-film transistors

Surface potentials of an operating In-Sn-O channel ferroelectric-gate transistor (FGT) were mapped by Kelvin probe force microscopy. We clearly observed a gradual transition within the channel from linear potential profile to superlinear ones when drain voltage approaches and overcomes gate voltage, which is related to the physics of electronic transport under field-effect doping. The dependence of field-effect mobility on gate-bias and lateral field, as well as the effect of source/drain electrode materials on transport properties, was also elucidated. This study provides useful information for optimizing the FGT performance and for understanding its underlying physics.

Anisotropic field effect mobility in single crystal pentacene

Fan-shaped electrodes were designed on Si∕SiO2 substrate to measure the anisotropic field effect mobility in freestanding single crystal pentacene. Field effect transistor was fabricated by placing single crystal pentacene on the prepatterned electrodes. The contact between the electrodes and single crystal pentacene was enhanced by applying pressure. Angle dependence of field effect mobility in single crystal pentacene showed remarkably anisotropic behavior. The highest mobility value was estimated to be ∼2.3cm2∕Vs at room temperature.

Interpretation of mechanism determining field effect mobility in a-Si:H TFT based on surface reaction model

The dependence of field effect mobility in thin film transistors (TFTs) on deposition conditions of active a-Si:H layers, i.e., rf power, gas flow rate and gas pressure, was studied. The mechanism determining the mobility has been studied in relation to the film growth conditions of a-Si:H and interpreted in terms of the surface reaction model. As an alternative material to a-Si:H, microcrystalline Si was applied to TFTs and the characteristics were compared to a-Si:H TFTs.

Effect of different methods of oxidation on SiSiO 2 interface state properties

Three different methods of oxidation - thermal, TCE, and anodic — were applied to n-type (111) silicon 10 ohm cm resistivity samples. MOS test samples were fabricated and their interface state properties were characterized by C- V and AC field effect techniques. From C- V measurements the interface state density at mid gap was found to be less in TCE (2 × 10 10 cm −2 eV −1) and anodic (1 × 10 10 cm −2 eV −1) samples than in dry (5 × 10 10 cm −2 eV −1) oxidized samples. The mobile charges were also less in TCE (2 × 10 10 cm −2) and anodic (5 × 10 10 cm −2) samples. Using the AC field effect technique, the frequency (2–100 kHz) and temperature dependence of field effect mobility, μ FE, were studied. By applying Garrett's theory of frequency dependence of μ FE, the relaxation times of interface states were found to vary from 30 to 3 μs in dry, 8 to 4 μs in TCE, and 4.5 to 1.5 μs in anodic samples in the temperature range 230 to 370 K. Using Rupprecht's theory of temperature dependence of relaxation times, thedominant energy levels, E c - E T , were found to be shallower in TCE (0.04 eV) and anodic (0.06 eV) than in dry (0.1 eV) oxidized samples. The capture cross-section of these samples was found to be small, in the range 10 −20 to 10 −21 cm 2. In TCE and anodic samples the shallow interface state levels indicate stronger interactions between silicon and oxygen atoms at the interface. The observed low densities of interface states and mobile charges in these samples also show improved passivation of silicon.

On the Limiting of Minimum Size of SOS/MOS Devices by the Microtwins in the Silicon

Plan view TEM micrographs of operating SOS/MOS transistors clearly show the extent and distribution of the silicon microtwins throughout the junction and channel regions. Numerous microtwins are found in the junctions without causing any detectible electrical problems. It is suggested that these defects will probably not be a fundamental limitation to geometrical reduction of SOS/ MOS devices. The twins cause a dependence of field effect mobility on current flow direction.