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Rubrene is one of the leading organic semiconductors in scientific and industrial research, showing good conductivities and utilities in devices such as organic field-effect transistors. In these applications, the rubrene crystals often contact ionic liquids and other materials. Consequently, their surface properties and interfacial interactions influence the device's performance. Although rubrene has been extensively studied with multiple structure characterization techniques, a complete description of the structure of rubrene single-crystal surfaces at the molecular level remains elusive. This study elucidates the molecular orientation and arrangement on the surface of rubrene single crystals with sum frequency generation (SFG) spectroscopy and reflection high-energy electron diffraction, respectively. The results confirm the near-surface unit cells with in-plane lattice parameters of a = 7.24 Å and b = 14.3 Å and an out-of-plane constant of c = 26.9 Å. Furthermore, the SFG analysis yields the tilt and rotation angles of θ = 15° and φ = 43° with respect to the crystalline c and a axes, respectively, and an in-plane twist of ψ = 3° for the surface phenyl rings. [ABSTRACT FROM AUTHOR]

Organic multilayer systems, which are stacked layers of different organic materials, are used in various organic electronic devices such as organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs). In particular, OFETs are promising as key components in flexible electronic devices. In this study, we investigated how the inclusion of an insulating tetratetracontane (TTC) interlayer in ambipolar indigo-based OFETs can be used to alter the crystallinity and electrical properties of the indigo charge transport layer. We find that the inclusion of a 20-nm-thick TTC film thermally annealed at a low temperature of 70 °C acts to significantly increase the ambipolar electrical transport of the indigo layer. X-ray diffraction, atomic force microscopy, and vibrational sum frequency generation measurements showed that annealing the TTC film significantly improved its ordering. The electronic sum-frequency generation spectra of TTC/indigo bilayers show that this improved ordering of TTC films promotes the growth of crystalline indigo films that exhibit charge mobilities in OFET that are nearly an order of magnitude larger than those measured for devices grown on unannealed TTC layers. Furthermore, using vibrational sum-frequency generation spectroscopy, we found that pre-annealing the TTC layer prior to indigo deposition can suppress the formation of defects within the TTC layer during indigo film growth, which also contributes to enhanced charge transport. Our results highlight the importance of controlling the molecular ordering within the interlayer contacts in OFET structures to achieve an enhanced performance. [ABSTRACT FROM AUTHOR]

Alkylated benzothienobenzothiophenes are an important class of organic semiconductors that exhibit high performance in solution-processed organic field-effect transistors. In this work, we study the near-edge x-ray absorption fine-structure (NEXAFS) spectra of 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) at both the carbon and sulfur K-edges. Angle-resolved experiments of thin films are performed to characterize the dichroism associated with molecular orientation. First-principles calculations using the density functional theory-based many-body x-ray absorption spectroscopy (MBXAS) method are also performed to correlate the peaks observed and their dichroism with transitions to specific antibonding molecular orbitals. Interestingly, the dichroism of the dominant, lowest energy peak is opposite at the carbon and sulfur K-edges. While the low-energy peak at the carbon K-edge is assigned to carbon 1s → π* transitions with transition dipole moment (TDM) perpendicular to the planar BTBT core, the dominant low energy peak at the sulfur K-edge is assigned to sulfur 1s → σ* transitions with TDM oriented along the long axis of the BTBT core. These differences at the sulfur and carbon K-edges are understood through the MBAXS simulations that find a reordering of the energy of the lowest energy π* and σ* transitions at the sulfur K-edge due to the strong localization of the σ* orbital over the sulfur atom. This work highlights differences in the NEXAFS spectra of organic semiconductors at carbon and sulfur K-edges and provides new insights into peak assignment and x-ray dichroism relevant for studying the molecular orientation of organic semiconductor films. [ABSTRACT FROM AUTHOR]

The semiconductor/insulator blends for organic field-effect transistors are a potential solution to improve the charge transport in the active layer by inducing phase separation in the blends. However, the technique is less investigated for long-chain conducting polymers such as Poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPPDTT), and lateral phase separation is generally reported due to the instability during solvent evaporation, which results in degraded device performance. Herein, we report how to tailor the dominant mechanism of phase separation in such blends and the molecular assembly of the polymer. For DPPDTT/PMMA blends, we found that for higher DPPDTT concentrations (more than 75%) where the vertical phase separation mechanism is dominant, PMMA assisted in the self-assembly of DPPDTT to form nanowires and micro-transport channels on top of PMMA. The formation of nanowires yielded 13 times higher mobility as compared to pristine devices. For blend ratios with DPPDTT ≤ 50%, both the competing mechanisms, vertical and lateral phase separation, are taking place. It resulted in somewhat lower charge carrier mobilities. Hence, our results show that by systematic tuning of the blend ratio, PMMA can act as an excellent binding material in long-chain polymers such as DPPDTT and produce vertically stratified and aligned structures to ensure high mobility devices. [ABSTRACT FROM AUTHOR]

The delafossite semiconductor CuInO 2 has shown great potential in transparent electronics for its bipolar dopability. However, little is known about the limiting factors about its carrier mobility, which impedes its further development. Applying a b i n i t i o Boltzmann transport formalism, here we calculate the intrinsic, phonon-limited carrier mobility of CuInO 2 and study its carrier–phonon coupling mechanisms. The calculated room-temperature electron and hole mobilities along the in-plane direction are μ e = 97.6 cm 2 V − 1 s − 1 and μ h = 1.4 cm 2 V − 1 s − 1 , respectively. We find that the electron mobility is limited by the combination of acoustic phonons and polar longitudinal optical (LO) phonons, while the hole mobility is mainly limited by carrier–acoustic phonon scattering. We further show that the electron effective mass and bandgap of CuInO 2 can be tuned through strain engineering for improved carrier transport properties. Our work uncovers the underlying factors that govern the intrinsic carrier mobility of the transparent bipolar semiconductor CuInO 2 and sheds light on the design and exploration of bipolar conducting transparent conductive oxides (TCOs) based on delafossite semiconductors. [ABSTRACT FROM AUTHOR]

The delafossite semiconductor CuInO 2 has shown great potential in transparent electronics for its bipolar dopability. However, little is known about the limiting factors about its carrier mobility, which impedes its further development. Applying a b i n i t i o Boltzmann transport formalism, here we calculate the intrinsic, phonon-limited carrier mobility of CuInO 2 and study its carrier–phonon coupling mechanisms. The calculated room-temperature electron and hole mobilities along the in-plane direction are μ e = 97.6 cm 2 V − 1 s − 1 and μ h = 1.4 cm 2 V − 1 s − 1 , respectively. We find that the electron mobility is limited by the combination of acoustic phonons and polar longitudinal optical (LO) phonons, while the hole mobility is mainly limited by carrier–acoustic phonon scattering. We further show that the electron effective mass and bandgap of CuInO 2 can be tuned through strain engineering for improved carrier transport properties. Our work uncovers the underlying factors that govern the intrinsic carrier mobility of the transparent bipolar semiconductor CuInO 2 and sheds light on the design and exploration of bipolar conducting transparent conductive oxides (TCOs) based on delafossite semiconductors. [ABSTRACT FROM AUTHOR]

Designing organic semiconductors for practical applications in organic solar cells, organic field-effect transistors, and organic light-emitting diodes requires understanding charge transfer mechanisms across different length and time scales. The underlying electron transfer mechanisms can be efficiently explored using semiempirical quantum mechanical (SQM) methods. The dimer projection (DIPRO) method combined with the recently introduced non-self-consistent density matrix tight-binding potential (PTB) [Grimme et al., J. Chem. Phys. 158, 124111 (2023)] is used in this study to evaluate charge transfer integrals important for understanding charge transport mechanisms. PTB, parameterized for the entire Periodic Table up to Z = 86, incorporates approximate non-local exchange, allowing for efficient and accurate calculations for large hetero-organic compounds. Benchmarking against established databases, such as Blumberger's HAB sets, or our newly introduced JAB69 set and comparing with high-level reference data from ωB97X-D4 calculations confirm that DIPRO@PTB consistently performs well among the tested SQM approaches for calculating coupling integrals. DIPRO@PTB yields reasonably accurate results at low computational cost, making it suitable for screening purposes and applications to large systems, such as metal-organic frameworks and cyanine-based molecular aggregates further discussed in this work. [ABSTRACT FROM AUTHOR]

Using Bayesian spectroscopy, we performed spectral decomposition of gate modulation (GM) spectra measured in a pentacene organic field-effect transistor to understand comprehensively the optical nonlinear response due to GM and hole injection. Although GM spectra contain a variety of spectral components, by Bayesian spectroscopy, we can specify the role of each component in the nonlinear response by performing model selection that chooses the spectral components needed to explain the data without preconceptions. For a GM spectrum under positive GM, Bayesian spectroscopy shows that nonlinear responses by the change in polarizability dominate the GM spectrum among several types of Stark signals induced by the GM electric field, which is a physically valid conclusion. For GM spectra under negative GM where gate-induced carriers are injected, Bayesian spectroscopy succeeds in completely elucidating the spectral structure, which is composed of the two types of Stark signals due to changes in the polarizability and the dipole moment, bleaching, and gate-induced absorption signals. A pentacene film is known to have solid and isolated molecular phases, which may give different spectral responses. Therefore, we compared a model that treats these responses equally and a model that distinguishes them. Bayesian spectroscopy selects the latter models for all GM spectra, revealing statistically that nonlinear optical effects and hole injection effects are different in these phases. [ABSTRACT FROM AUTHOR]

Organic ferroelectric field-effect transistors (Fe-OFETs) exhibit exceptional capabilities in mimicking biological neural systems and represent one of the primary options for flexible artificial synaptic devices. Ferroelectric polymers, such as poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), given their strong ferroelectricity and facile solution processing, have emerged as the preferred choices for the ferroelectric dielectric layer of wearable devices. However, the solution processed P(VDF-TrFE) films can lead to high interface roughness, prone to cause excessive gate leakage. Meanwhile, the ferroelectric layer in neural computing and memory applications also faces a trade-off between storage time and energy for read/write operations. This study introduces a composite dielectric layer for Fe-OFETs, fabricated via a solution-based process. Different thicknesses of poly(N-vinylcarbazole) (PVK) are shown to significantly alter the ferroelectric hysteresis window and leakage current. The optimized devices exhibit synaptic plasticity with a transient current of 3.52 mA and a response time of approximately 50 ns. The Fe-OFETs with the composite dielectric were modeled and integrated into convolutional neural networks, achieving a 92.95% accuracy rate. This highlights the composite dielectric's advantage in neuromorphic computing. The introduction of PVK optimizes the interface and balances device performance of Fe-OFETs for neuromorphic computing. [ABSTRACT FROM AUTHOR]

The development of complementary metal-oxide-semiconductor field-effect transistor (CMOSFET) based on two-dimensional (2D) materials offers an important opportunity to reduce static power and increase the integration density of integrated circuits. One promising approach to realize these CMOSFETs is to employ ambipolar 2D materials as channel materials with designed device structure to control the carrier transport properties for CMOSFET characteristics. However, these devices always suffer from complex multi-gate electrode structure, and hence face challenges in complicated inter-connection design and excessive voltage source requirement for circuit implementation. Here, we develop a three-terminal CMOSFET using ambipolar 2D material based on the drain electric field-induced carrier injection self-blocking mechanism. The designed drain electrode can effectively suppress carrier injection from the drain to the channel material, while the gate voltage can only regulate carrier injection in the source region. As a result, we can configure the device as either N-field-effect transistors (FET) or P-FET with a high current on/off ratio of over 105 by adjusting the three voltages (gate, source, and drain). Furthermore, we utilize these devices to demonstrate multifunctional wave modulator, low-static-power logic inverter (<5 pW), and combinational logic computing in the form of a compact complementary circuit. Our work would explore an efficient approach for implementing complementary circuits using 2D materials. [ABSTRACT FROM AUTHOR]

Demonstration of acoustically improving charge transport characteristics of regioregular poly(3-hexylthiophene) (rrP3HT) based organic field effect transistor (OFET) fabricated on YZ lithium niobate piezoelectric substrate has been presented and analyzed. Owing to the acoustoelectric (AE) effect, a surface acoustic wave (SAW) propagating through the substrate transfers its momentum and energy to the charges in the rrP3HT channel, reducing the effective energy gap between the charge hopping states, which leads to a decrease in charge trapping and an increase in path conductivity and number of paths for charge transport. Hence, a significant increase in drain current and mobility and a substantial reduction in gate voltage were observed in the presence of SAW. The AE effect has been especially predominant in devices with smaller channel width, depicting that gate voltage brought down by 30 V provided drain current equivalent to that obtained in the absence of SAW. The bias stress analysis of the devices showed an increase in current instead of the decrease, generally seen with respect to time, reinforcing that the long term charge trapping effect in OFETs can be compensated with the propagation of SAW leading to enhanced device stability. [ABSTRACT FROM AUTHOR]

Epitaxial graphene (EG) on cubic silicon carbide (3C-SiC) on silicon holds the promise of tunable nanoelectronic and nanophotonic devices, some uniquely unlocked by the graphene/cubic silicon carbide combination, directly integrated with the current well-established silicon technologies. Yet, the development of graphene field-effect devices based on the 3C-SiC/Si substrate system has been historically hindered by poor graphene quality and coverage, as well as substantial leakage issues of the heteroepitaxial system. We address these issues by growing EG on 3C-SiC on highly resistive silicon substrates using an alloy-mediated approach. In this work, we demonstrate a field-effect transistor based on EG/3C-SiC/Si with gate leakage current 6 orders of magnitude lower than the drain current at room temperature, which is a vast improvement on the current literature, opening the possibility for dynamically tunable nanoelectronic and nanophotonic devices on silicon at the wafer level. [ABSTRACT FROM AUTHOR]

Charge modulation microscopy (CMM) is an electro-optical method that is capable of mapping the spatial distribution of induced charges in an organic field-effect transistor (OFET). Here, we report a new (and simple) implementation of CMM in transmission geometry with camera-based imaging. A significant improvement in data acquisition speed (by at least an order of magnitude) has been achieved while preserving the spatial and spectral resolution. To demonstrate the capability of the system, we measured the spatial distribution of the induced charges in an OFET with a polymer blend of indacenodithiophene-co-benzothiadiazole and poly-vinylcarbazole that shows micrometer-scale phase separation. We were able to resolve spatial variations in the accumulated charge density on a length scale of 500 nm. We demonstrated through a careful spectral analysis that the measured signal is a genuine charge accumulation signal that is not dominated by optical artifacts. [ABSTRACT FROM AUTHOR]

Graphene provides a unique platform for hosting high quality 2D electron systems. Encapsulating graphene with hexagonal boron nitride (hBN) to shield it from noisy environments offers the potential to achieve ultrahigh performance nanodevices, such as photodiodes and transistors. However, the absence of a bandgap at the Dirac point presents challenges for using this system as a useful transistor. In this study, we investigated the functionality of hBN-aligned monolayer graphene as a field effect transistor (FET). By precisely aligning the hBN and graphene, bandgaps open at the first Dirac point and at the hole-doped induced Dirac point via an interfacial moiré potential. To characterize this as a submicrometer scale FET, we fabricated a global bottom gate to tune the density of a conducting channel and a local top gate to switch off this channel. This demonstrated that the system could be tuned to an optimal on/off ratio regime by separately controlling the gates. These findings provide a valuable reference point for the further development of FETs based on graphene heterostructures. [ABSTRACT FROM AUTHOR]

Due to their functional and processing versatility, organic semiconductors have gained much interest in recent years. Tailoring the charge transport in a polymeric semiconductor system is imperative for developing optimized devices. Factors such as selection of solvent species and annealing temperature play a significant role in deciding the morphology of the polymer semiconductor and hence the device performance. Bottom-gate bottom-contact organic field-effect transistors were fabricated with regioregular poly(3-hexylthiophene) (P3HT) as the active material. The effects of using chlorobenzene and o-dichlorobenzene as the solvents for P3HT and annealing temperatures on the device performance were evaluated. The devices made using chlorobenzene showed greater field-effect mobility compared to those fabricated with o-dichlorobenzene. This behavior can be attributed to the disentanglement of polymer chains in a solvent with better matching solubility parameters and subsequent ease of arranging in ordered structures during processing. Furthermore, annealing the o-dichlorobenzene devices at temperatures closer to the crystallization temperature of P3HT showed an increase in field-effect mobility. At temperatures closer to the crystallization temperature, a polymer film in a semidry state can allow increased ordering of the chains leading to enhanced charge transportation. [ABSTRACT FROM AUTHOR]

The imperative for continuous device miniaturization has heightened the need for logic reconfigurability due to its benefits in circuit design simplification and process optimization. Van der Waals ambipolar transistors, notable for their inherent reconfigurable characteristics, have garnered significant interest for their potential to revolutionize information electronics. Nevertheless, as the semiconductor thickness approaches the 3-nm mark, precise modulation of electrical polarity presents a considerable challenge as minor variations in thickness can lead to significant electrical disparities. Here, we introduce a silicon backend process-compatible approach by employing surface charge transfer doping to skillfully adjust the polarity in ambipolar transistors. This universal method can achieve a controllable p-type doping effect and good electrical symmetry in ambipolar semiconductors. Through careful calibration of the MoO3 dopant layer thickness, we significantly enhance the hole mobility in doped WSe2 field-effect transistors (FETs), increasing it from 8 to 100 cm2 V−1 s−1, surpassing the performance of most non-silicon p-type semiconductors. A thorough temperature-dependent doping characterization elucidates the deeper traps-induced Schottky barrier variation for hole transport, and a reduction in current fluctuation for electron transport in WSe2/MoO3 FETs. Leveraging the precision in electrical polarity control, we demonstrate a complementary logic inverter by integrating two doped ambipolar FETs on a single monolithic channel. This advancement paves the way for quasi-forksheet structures and underscores the benefits in evolving advanced processing technologies, steering toward scalable, cost-effective, and efficient electronic device fabrication. [ABSTRACT FROM AUTHOR]

Stochastic resonance (SR) is an intriguing phenomenon in which noise, typically considered a detrimental aspect of electronic communication systems, assumes a beneficial role in the detection of undetectable signals. The SR phenomenon for detecting low-intensity optical signals using PBTTT-C14-based organic field-effect transistors (OFETs) is being reported. In this discourse, we explicate the sensing of an undetectable periodic optical signal with a frequency of 5 Hz, using a PBTTT-C14-based OFETs in the presence of a finite and optimal quantity of Gaussian noise (noise bandwidth of 1 Hz and noise amplitude of 2.0, 4.0, 6.0, and 7.5 V). The detection of higher harmonics for optical signals using the SR phenomenon has not been hitherto explored for OFETs. This report presents a noteworthy finding elucidating the detection of the principal frequency and also higher harmonics of the optical signal. This simplistic methodology for examining the SR phenomenon holds great promise in identifying its robust utility in diverse real-world contexts. [ABSTRACT FROM AUTHOR]

Gas sensors based on ambipolar carbon nanotube (CNT) field-effect transistors with various amounts of CNTs were fabricated by dielectrophoretic assembly. The nitrogen dioxide (NO2) gas response and recovery properties of the transistors were measured to investigate the effect of CNT amount on gas response. For the device with a small amount of CNTs, responses from the CNT bulk and CNT/electrode contacts were observed. For devices with a large amount of CNTs, in which a network-like structure of CNTs was observed near the electrodes, an increased current in both electron and hole conduction regions was observed compared with that for the device with a small amount of CNTs. The increased current in the electron conduction region rapidly decreased during recovery. This response is consistent with that of CNT/CNT X-type contacts, which have a high resistance before NO2 adsorption. Equivalent circuits of CNT channels with CNT/CNT contacts were developed, allowing the transistor behavior to be qualitatively discussed. Evaluation of time constants revealed that CNT/electrode contacts and CNT/CNT X-type contacts exhibited high NO2 adsorption and desorption rates, respectively. [ABSTRACT FROM AUTHOR]

We propose a compact computational method based on the capacitance model for the efficient design of graphene-based synaptic field effect transistors (FETs), in which the hysteresis of conduction characteristics due to the channel–gate interface trap is used as synaptic plasticity. Using our method to calculate the conduction properties of graphene and armchair graphene nanoribbon (AGNR) superlattice FETs, it is shown that the AGNR can achieve an efficient conductance change rate Δ w , which is approximately 7.4 times that of graphene. It was also found that Δ w was the greatest when the gate oxide thickness was around 2–3 nm, which is near the limit of miniaturization. These results suggest that the proposed synaptic FETs are a promising approach to realize large scale integration chips for biological timescale computation. [ABSTRACT FROM AUTHOR]

The development of organic thin-film transistors (TFTs) for high-frequency applications requires a detailed understanding of the intrinsic and extrinsic factors that influence their dynamic performance. This includes a wide range of properties, such as the device architecture, the contact resistance, parasitic capacitances, and intentional or unintentional asymmetries of the gate-to-contact overlaps. Here, we present a comprehensive analysis of the dynamic characteristics of the highest-performing flexible organic TFTs reported to date. For this purpose, we have developed the first compact model that provides a complete and accurate closed-form description of the frequency-dependent small-signal gain of organic field-effect transistors. The model properly accounts for all relevant secondary effects, such as the contact resistance, fringe capacitances, the subthreshold regime, charge traps, and non-quasistatic effects. We have analyzed the frequency behavior of low-voltage organic transistors fabricated in both coplanar and staggered device architectures on flexible plastic substrates. We show through S-parameter measurements that coplanar transistors yield more ideal small-signal characteristics with only a weak dependence on the overlap asymmetry. In contrast, the high-frequency behavior of staggered transistors suffers from a more pronounced dependence on the asymmetry. Using our advanced compact model, we elucidate the factors influencing the frequency-dependent small-signal gain and find that even though coplanar transistors have larger capacitances than staggered transistors, they benefit from substantially larger transconductances, which is the main reason for their superior dynamic performance. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) hold great potential in various applications, including biosensing and neural network computation. Traditional "all-in-one" OECT device architecture faces the problems of unclear amplification mechanisms and complex side reactions, to name a few. The reaction cell OECT (RC-OECT) device architecture, proposed by Ting et al. [Adv. Funct. Mater. 31(19), 2010868 (2021)], effectively resolves these problems. Furthermore, in many applications of OECTs, such as high throughput (bio)sensing, an OECT device array instead of a single OECT is needed. Therefore, the size (area) of the OECT device, which represents the amount of occupied chip real estate and the integration of the device, matters. In this paper, we developed a hydrogen peroxide sensor based on the RC-OECT. We utilized an RC cathode modified by the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate film and a Ag/AgCl OECT gate electrode for facilitating device integration, varied RC anode area, and achieved optimization of at least one of the two parameters, sensitivity and lower limit of detection (LLoD), in conjunction with the level of integration of the device. Multiple quantitative sensitivity metrics have been adopted in this work. We also evaluated the correlation between RC anode area and LLoD. In addition, a mechanistic analysis of the RC-OECT device structure, in terms of faradic and non-faradaic currents, was carried out to illustrate the interplay between sensing performance and the electrode area of the reaction cell. This mechanistic analysis provides insights for miniaturizing OECT devices with the RC-OECT architecture. [ABSTRACT FROM AUTHOR]

Two-dimensional layered ReX2 (X = Se, S) has attracted researcher's great interest due to its unusual in-plane anisotropic optical and electrical properties and great potential in polarization-sensitive optoelectronic devices, while the clean, energy-saving, and ecological synthesis of highly crystalline ReSe2 with controlled domains remains challenging. Here, we develop a space-confined solid-phase approach for growing high-quality two-domain 1T′-ReSe2 with tunable optoelectronic properties by using pure Re powder as a Re precursor. The results show that ReSe2 can be grown at a temperature as low as 550 °C in a small-tube-assisted space-confined reactor, with its size and shape well-tailored via temperature control. A solid-phase two-domain ReSe2 growth mechanism is proposed, as evidenced by combining in situ optical monitoring, ex situ electron microscope, elemental mapping, and polarized optical imaging. Moreover, two-domain ReSe2 transistors are fabricated, which exhibit a switchable transport behavior between n-type and ambipolar character via grain boundary orientation control. This modulation phenomenon is attributed to the different doping levels between grain boundary and single domain. Furthermore, our two-domain ReSe2 photodetectors exhibit a highly gate-tunable current on–off ratio (with a maximum value of ∼8.2 × 103), a polarization-sensitive photo-response, and a high-speed response time (∼300 μs), exceeding most of the previously reported ReX2 photodetectors. Our work, thus, provides a low-consumption, energy-saving growth strategy toward high-quality, domain-controlled ReX2 for highly tunable and high-performance optoelectronics. [ABSTRACT FROM AUTHOR]

As transistor footprint scales down to the sub-10 nm regime, the process development for advancing to further technology nodes has encountered slowdowns. Achieving greater functionality within a single chip requires concurrent development at the device, circuit, and system levels. Reconfigurable transistors possess the capability to transform into both n-type and p-type transistors dynamically during operation. This transistor-level reconfigurability enables field-programmable logic circuits with fewer components compared to conventional circuits. However, the reconfigurability requires additional polarity control gates in the transistor and potentially impairs the gain from a smaller footprint. In this paper, we demonstrate a 2D control-gate-free reconfigurable transistor based on direct modulation of out-of-plane conduction in an ambipolar MoTe2 channel. Asymmetric electrostatic gating at the source and drain contacts is employed in the MoTe2 transistor resulting in different Schottky barrier widths at the two contacts. Consequently, the ambipolar conduction is reduced to unipolar conduction, where the current flow direction determines the preferred carrier type and the transistor polarity. Temperature dependence of the transfer characteristics reveals the Schottky barrier-controlled conduction and confirms that the Schottky barrier widths at the top contact are effectively tuned by electrostatic gating. Without the complexity overhead from polarity control gates, control-gate-free reconfigurable transistors promise higher logic density and lower cost in future integrated circuits. [ABSTRACT FROM AUTHOR]

SmB6, a topological Kondo insulator, possesses topologically protected surface states, in which carrier mobility is supposed to be high but is significantly varied in orders of magnitude dependent upon characterization methods. Herein, we performed magnetoresistance measurements on a Hall-bar device constructed on a highly uniform SmB6 nanoribbon with (001) surface grown by chemical vapor deposition. Unusual non-linear Hall resistance was observed at low temperature and explained with a two-carrier model. The two types of carriers were attributed to two types of Fermi pockets on the Brillouin zone of the SmB6 (001) surface. The Fermi pocket on Γ point provided high hole mobility up to 1.4 × 10 3 cm2/V s but low hole density at a temperature of 2.2 K. On the other hand, the Fermi pockets on X points supplied low electron mobility down to 1.8 cm2/V s but high electron density. The identification of the two types of pockets laid the foundation for the understanding of the transport via the topological surface states of the SmB6 (001) surface. [ABSTRACT FROM AUTHOR]

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO 2 , has been replaced by solid electrolytes, such as LiP 3 O 4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO 2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO 2 -gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li + ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability. [ABSTRACT FROM AUTHOR]

The high capacitance from an electrolyte dielectric layer used in a thin film transistor architecture results in the development of electrolyte-gated organic field effect transistors (EGOFETs), which are able to operate at lower voltages compared with the commonly organic field effect transistors. When ions diffuse into the semiconductor, changing its conductive properties, the resulting devices are named organic electrochemical transistors (OECTs). In this case, an increase in channel conductivity occurs due to ionic doping. Depending on the gate voltage range operation, it is possible to obtain a de-doping process, suitable for achieving a low off-current. In this work, a simple and easy method is proposed based on an additional dielectric layer deposition of poly(methyl methacrylate) at the electrolyte dielectric/semiconductor interface, which provides: (i) good efficiency to block the diffusion of anions into the channel, resulting in an EGOFET for a gate voltage range up to − 0.6 V and (ii) an improvement in the on–off ratio in approximately three orders of magnitude for OECTs due to the low off-current obtained without promoting ionic de-doping in the channel, for a gate voltage range up to − 1.1 V. Both modes of operation were obtained in the same transistor structure. In addition, parameters such as field effect mobility, on–off ratio, and threshold voltage were also estimated for different transistor structures and gate voltage ranges. [ABSTRACT FROM AUTHOR]

Zinc is often regarded as an alternative to magnesium p-type dopants in gallium nitride. However, besides many theoretical predictions, at present, there are poor data on experimentally revealed p-type conductivity and evaluation of Zn activation energy by means of electrical transport measurements. In this paper, ammonothermal crystallization of bulk GaN:Zn monocrystals is reported. Despite a high doping level of Zn (up to 2 × 1020 cm−3), p-type conductivity with hole concentration as low as of 4 × 1015 cm−3 at room temperature and mobility about 3 cm2/V s was observed. A deep nature of the Zn acceptor was proved, as the ionization energy can exceed 260 meV. In addition, conduction in the impurity band appeared at temperatures as high as room temperature. [ABSTRACT FROM AUTHOR]

Transistor-based artificial synapses are expected to tackle the inherent limitations of traditional von Neumann architecture for neuromorphic computing paradigm. Organic electronic materials are promising components of future neuromorphic systems, but mimicking the functions of biological synapses for symmetric weight update and desired variation margin still remains challenging. Here, we propose a synaptic transistor based on pentacene/poly(α-methylstyrene) (PαMS) architecture capable of exhibiting the main behavior of a biological spiking synapse. The ambipolar charge trapping of the transistor enables symmetric variation of the channel conductivity with desirable margin. Comprehensive synaptic functions, including the postsynaptic current with different pulse amplitudes, short-term to long-term plasticity transition, reversible channel conductance potentiation and depression, and repetitive and symmetrical learning processes, are emulated. The realization of essential synaptic functions based on the cumulative charge trapping of pentacene/PαMS structure provides a feasible device structure toward the future demand of neuromorphic computing. [ABSTRACT FROM AUTHOR]

Improved charge carrier mobility of polymer semiconductors is often a critical factor in achieving superior performance for organic electronic devices. A novel low-temperature electric-field (LTEF) treatment on poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films, which helps in increasing hole mobility in these films, is presented herein. The zero-field hole mobility at room temperature of the polymer film in a "hole-only" device configuration is found to increase by more than seven times from 1.1 × 10−4 to 7.8 × 10−4 cm2 V−1 s−1 following the application of an electric field strength of 2 × 105 V cm−1 across the films at low temperature (80 K). On the other hand, a room temperature electric field treatment of the devices does not appear to have any effect on the hole mobility in the PTB7 films. LTEF treatment is shown to help decrease the average barrier energy for charge carriers between adjacent molecular energy levels in the films from 302 to 266 meV, energy disorder from 53.2 to 49.3 meV, and position disorder from 2.1 to 1.7 in PTB7 films. The hole mobility improvement is attributed to the field induced enhanced order in those films by dipolar alignment, which is facilitated by higher polarization at low temperatures. [ABSTRACT FROM AUTHOR]

The electrical transport in graphene interfaced with different ions in solution gated graphene field effect transistors (GFETs) is the subject of active studies due to its importance in sensor fabrication. Most of the developed GFET biological sensors use graphene that has been modified. The difficulty in the modification procedure and the reduction in quality of graphene that it causes are important drawbacks for applications. Therefore, we focus on GFETs based on unmodified graphene gated by aqueous solutions containing lysine amino acids. We observed that an increase in the ionic concentration of lysine in these solutions leads to a suppression of unipolar electron conductance of graphene in GFETs. This dependence is opposite to the dependence typically observed in gating solutions containing smaller atomic ions. We attribute the observed suppression to electric field screening of the graphene surface from water molecules by lysine ions which are larger and have lower charge density compared to atomic ions. This novel phenomenon leads to an overall decrease of surface charge density in molecular layers formed at the graphene interface and can be applied in GFET sensors with unmodified graphene that detect the presence and concentration of large molecules in the gating solutions. [ABSTRACT FROM AUTHOR]

Field-effect transistor (FET)-based sensors allow rapid, label-free electrical detection of chemical and biological species and are easy to use. Dual-gate FET-based biosensors enable sensitive detection with high intensity signal by their distinctive structure based on a combination of solid and liquid gates. However, the underlying mechanism of signal amplification to explain the experimental results has not been well explained with theoretical analysis. In this work, a theoretical approach based on device physics is used to interpret the signal enhancement in dual-gate FET-based biosensors. The analysis is verified with a simulation method for pH sensors based on a well-established commercialized semiconductor 3D technology computer-aided design simulation. The pH sensing parameters are comprehensively investigated as a function of the electrical characteristics of dual-gate FETs: the voltage, current, and normalized current signals are directly correlated with capacitive coupling, transconductance, and subthreshold swing, respectively. Our theoretical analysis provides design guidelines for sensitive dual-gate FET-based biosensors. [ABSTRACT FROM AUTHOR]

We report transport measurements of ionic liquid-gated field-effect transistors with multilayer MoS2 channels. Ambipolar characteristics with high ON/OFF ratios (>105) are observed. The current–voltage characteristics agree well with those calculated using a simple model assuming a high recombination probability and negligible contact resistance, except when holes are doped in the vicinity of the source contact. Electron and hole mobilities are estimated using the current–voltage characteristics in both the unipolar and ambipolar modes, wherein a p–n junction is formed in the latter. The electron mobility depends significantly on the carrier distribution in a channel that is controlled by the gate voltage. This result is attributed to the significant field dependence of the electron mobility. [ABSTRACT FROM AUTHOR]

CdxZn1−xTeySe1−y (CZTS) has emerged as a next-generation compound semiconductor for high energy gamma-ray detection. In the present study, we report for the first time the hole transport property measurements in CZTS based gamma-ray detectors in the planar configuration. Current–voltage measurements revealed a bulk resistivity of ∼5 × 108 Ω cm and the fabricated detectors produced well-resolved 5486 keV alpha particle peaks, for both electrons and holes drifting alike, when pulse-height spectra (PHS) were recorded using a 241Am radiation source. The PHS measurements were enabled to measure the charge transport properties for both the charge carriers. The mobility–lifetime product (μτ) for electrons and holes was calculated to be 6.4 × 10−4 cm2 V−1 and 8.5 × 10−5 cm2 V−1, respectively, using a single polarity Hecht plot regression method. The pre-amplifier pulses were also recorded and processed digitally to obtain electron and hole drift mobilities of 692 cm2 V−1 s−1 and 55 cm2 V−1 s−1, respectively, using a time-of-flight method. The measured transport properties indicated the hole lifetime to be greater than the electron lifetime by a factor of ∼1.5. Gamma-ray PHS were recorded using fabricated detectors that showed tailing of the 662 keV photopeak due to hole trapping effects. Depth dependent PHS were digitally generated from 2D biparametric plots to reveal the effects of hole trapping on the gamma PHS at different detector depths. Digital correction procedures were applied to generate well-resolved PHS with an energy resolution of ∼2% for 662 keV γ-rays. [ABSTRACT FROM AUTHOR]

AlScN/GaN heterostructures are worth investigating due to the remarkable high gradients in spontaneous polarization at their interfaces, which brings them into play for a wide field of potential high-power and high-frequency electronic applications. In this work, AlScN/GaN heterostructures for high electron mobility transistor (HEMT) structures were grown by metalorganic chemical vapor deposition. We have investigated the impact of growth parameters on thick AlScN layers and on thin AlScN/GaN heterostructures. Growth parameters, such as temperature, V/III ratio, pressure, and growth mode, were varied with the focus on surface morphology, crystal quality, and incorporation of impurities. High growth temperatures improve the surface quality and reduce impurities incorporation notably. In addition to that, a slight decrease in carbon concentration is obtained by adopting a pulsed supply of metalorganic precursors. V/III ratio and pressure did not influence the layer quality observably. Heterostructures with root mean square surface roughness values as low as 0.38 nm, revealing smooth growth steps, were achieved. The presence of two-dimensional electron gases with sheet carrier densities and mobilities of up to 2 × 1013 cm−2 and close to 900 cm2/(V s), respectively, resulted in channel sheet resistances as low as 337 Ω/sq, very suitable for AlScN/GaN HEMTs. Heterostructures with sheet resistances below 200 Ω/sq and sheet carrier densities of 5 × 1013 cm−2 were also achieved but showed significantly lower mobility. [ABSTRACT FROM AUTHOR]

It is shown that the dynamic response of a thin-film transistor (TFT) comprises a polymer or organic semiconductor and can be directly correlated with charge transport parameters. Charge transport is assumed to take place in accordance with the often employed multiple trap and release model. We can simulate the non-quasistatic response of TFTs for devices in which the mobility is not constant, but depends on carrier density and other parameters. The previous model of Burns has been significantly improved and made applicable to organic and polymer transistors. Our approach works for an arbitrary density of states including both a relatively shallow exponential distribution of tail states and deeper Gaussian trap states. We set the gate voltage, VG, in our TFTs to be zero. The source voltage, VS, is varied and, thus, the value of gate-to-source voltage is varied. The predictive power of the model that is presented in this paper will be very useful for accurate device modeling and for charge transport studies. [ABSTRACT FROM AUTHOR]

The light-induced synaptic transistors, with their large-scale and cost-effective benefits, hold significant promise for advancing neuromorphic electronics. In this work, we propose a hybrid phototransistor with a channel layer composed of C8-BTBT and PM6. This device exhibits an extended optical response range in comparison to pure C8-BTBT transistors. In addition, the device shows excellent synaptic plasticity under red, green, and blue light stimuli, with the potential for tuning through light dosage and pulse duration. The study further confirms consistent device performance and reliable operation. Moreover, we show that this type of device can be fabricated into array to write the letters "C", "S", and "U" and store red, green, and blue information. These experimental results show the excellent responsiveness and storage performance of our devices under red, green, and blue light stimuli, suggesting promising applications in artificial vision. [ABSTRACT FROM AUTHOR]

We demonstrated that the carrier polarity of MoTe2 transistors can be modulated by controlling the channel thickness with NiTe2 semimetal contacts. The multilayer MoTe2 transistors (thickness >7.1 nm) exhibit a symmetric ambipolar conduction, and a transition to unipolar p-type polarity occurs as the channel thickness decreased down to ∼2.3 nm. The position of the semimetal NiTe2 work function was verified to be located at the mid-gap of multilayer MoTe2, and the observed transition was interpreted by a synergistic effect of the channel thickness-dependent band alignment and charge transfer behavior with unique NiTe2 semimetal contacts. [ABSTRACT FROM AUTHOR]

Artificial intelligence technology has fueled the requirement for flexible hardware. Although flexible electronic devices have become promising candidates in recent years, they inevitably face problems like performance degradation caused by deformation. In this paper, we report a stable performance and flexible indium tin oxide synaptic transistor with an ultralow back-sweep subthreshold swing of 28.52 mV/dec, which is ascribed to the positive charge trapping/de-trapping effect introduced by a naturally oxidized Al2O3 layer. Even after bending 1 × 103 times, the flexible artificial synapse shows stable electrical performance without evident attenuation. Furthermore, the synaptic transistor exhibits good compatibility with an external thin-film pressure sensor, and their combination empowers the device to realize tactile sensing, which can achieve the function of Braille code recognition. Evidently, the reported flexible synaptic transistor demonstrates its potential for artificial perception processing. [ABSTRACT FROM AUTHOR]

The interfacial region between two bulk media in organic semiconductor based devices, such as organic field-effect transistors (OFETs), organic light-emitting diodes, and organic photovoltaics, refers to the region where two different materials such as an organic material and an electrode come in contact with each other. Although the interfacial region contains a significantly smaller fraction of molecules compared to the bulk, it is the primary site where many photoinduced excited state processes occur, such as charge transfer, charge recombination, separation, energy transfer processes, etc. All such photoinduced processes have a dependence on molecular orientation and density of states at the interfaces, therefore having an understanding of the interfacial region is essential. However, conventional spectroscopic techniques, such as surface-enhanced Raman scattering, x-ray photoelectron spectroscopy, atomic force microscopy, etc., face limitations in probing the orientation and density of states of interfacial molecules. Therefore, there is a need for noninvasive techniques capable of efficiently investigating the interfaces. The electronic sum frequency generation (ESFG) technique offers an interface selectivity based on the principle that the second-order nonlinear susceptibility tensor, within the electric dipole approximation, is zero in the isotropic bulk but nonzero at interfaces. This selectivity makes ESFG a promising spectroscopy tool to probe the molecular orientation and density of states at the buried interface. For beginners interested in employing ESFG to study the density of states at the interface, a detailed description of the experimental setup is provided here. [ABSTRACT FROM AUTHOR]

The fullerene-based derivative phenyl-C61-butyric acid methyl ester (PCBM) has attracted attention as an n-type transistor channel and an organic photovoltaic material due to its solution processability, stability, and high electron mobility. However, disorder in solution-processed PCBM thin films makes understanding of charge carrier transport mechanisms difficult. We have fabricated PCBM-based field effect transistors and improved device performance by reducing electron trapping at the dielectric–semiconductor interface and improving charge carrier injection. Single-wall carbon nanotubes were successfully integrated into conventional gold electrodes to improve injection efficiency. Meyer–Neldel behavior has been investigated in a study of charge carrier transport in PCBM thin films. Crystallization of PCBM was observed during the measurement. We find that charge carriers hop between molecules in mostly amorphous regions from 145 to 240 K. The transport is facilitated by the formation of more crystallized regions when samples are heated as high as 240 K. [ABSTRACT FROM AUTHOR]

This study examines the low-frequency noise characteristics of the 2,7-dioctyl[1] benzothieno[3,2-b][1] benzothiophene organic thin-film transistor (OTFT) having a CYTOP dielectric layer. Specifically, the fabricated OTFT exhibits 1/f noise, and its behavior is explained via a carrier number fluctuation model. Additionally, the volume trap density (NT) of the gate dielectric is quantitatively evaluated and compared with its counterpart having SiO2 dielectric layer. The analysis of the results shows that the hydrophilic entities of the dielectric layer strongly influence the NT, while the CYTOP having hydrophobic properties provides less NT than that of SiO2. [ABSTRACT FROM AUTHOR]

We investigate the channel length dependence of the electrical characteristics of chemical vapor transport (CVT)-grown MoS 2 nanoribbon (NR) Schottky barrier field-effect transistors to provide insights into the transport properties of such nanostructures. The MoS 2 NRs form spontaneously during the CVT growth, without the application of etching. Back gated transmission line measurement FETs were fabricated on a 45 μ m -long NR with channel lengths ranging between 200 nm and 3 μ m. Contact and sheet resistances were extracted from the electrical measurements and their back-gate bias dependence was analyzed. Numerical modeling based on a virtual probe approach combined with the Landauer formalism shows excellent agreement with the measurements. The model enables a quantitative extraction of the intrinsic FET properties, e.g., mean-free-path and electron mobility, and their dependence on carrier density and investigation of plausible trap distributions. A record electron mobility for a MoS 2 NR channel of ∼ 81 cm 2 / V s was achieved. [ABSTRACT FROM AUTHOR]

Wearable electronic and optoelectronic devices accommodable to various mechanical deformations are becoming increasingly ubiquitous in various realms spanning electronic skins, electronic eyes, intelligent wristbands, lenses, smartphones/watches/glass, robotics, foldable screens, autonomous artificial intelligence systems, etc., which, however, are beyond the scope of conventional bulky semiconductors. Fortunately, 2D group 6 transition metal dichalcogenides (TMDCs) emerge as alternatives, having advantages of strong mechanical strength, high conformability, semitransparency, high biocompatibility, large surface-to-volume ratio, and favorable bandgaps. Highlighting an indispensable physical foundation for reliable wearability, this perspective begins with an elaboration on the structural and mechanical attributes of 2D TMDCs. Then, the latest research advancements of wearable electronic and optoelectronic devices built on them, including field-effect transistors, gas/ion/bio/tactile sensors, photodetectors, and proof-of-concept novel applications, such as electronic noses, flexible displays, and the underlying working mechanisms, are compactly surveyed. This leads us to come up with the predominant challenges standing in the way of further development, and strategies addressing them, along with associated physical principles that are comprehensively outlined. [ABSTRACT FROM AUTHOR]

Balanced charge transport is particularly important for transistors. Hence, ambipolar organic semiconductors with comparable transport capabilities for both positive and negative charges are highly sought-after. Here, we report detailed insights into the electronic structure of PNDITBT, which is an alternating copolymer of naphthalene diimide (NDI), thiophene, benzothiodiazole (B), and thiophene (T) units, as gained by time-resolved electron paramagnetic resonance (TREPR) spectroscopy combined with quantum-chemical calculations. The results are compared to those obtained for PNDIT2 and PCDTBT, which are derivatives without B and NDI acceptor units, respectively. These two polymers show dominant n- and p-channel behavior in organic field-effect transistors. The TBT moiety clearly dominates the electronic structure of PNDITBT, although less so than in PCDTBT. Furthermore, the triplet exciton most probably delocalizes along the backbone, exhibits a highly homogeneous environment, and planarizes the polymer backbone. Obtaining the zero-field splitting tensors of these triplet states by means of quantum-chemical calculations reveals the triplet energy sublevel associated with the molecular axis parallel to the backbone to be preferentially populated, while the one perpendicular to the aromatic plane is not populated at all, consistent with the spin-density distribution. PNDITBT consisting of two acceptors (NDI and B) has a complex electronic structure, as evident from the two charge-transfer bands in its absorption spectrum. TREPR spectroscopy provides a detailed insight on a molecular level not available by and complementing other methods. [ABSTRACT FROM AUTHOR]

The development of high-performance p-type oxides with high hole mobility and a wide bandgap is critical for the applications of metal oxide semiconductors in vertically integrated CMOS devices [Salahuddin et al., Nat. Electron. 1, 442 (2018)]. Sn2+-based oxides such as SnO and K2Sn2O3 have recently been proposed as high-mobility p-type oxides due to their relatively low effective hole masses, which result from delocalized Sn s-orbital character at the valence band edge. Here, we introduce a promising ternary Sn-O-X compound, Ta2SnO6, which exhibits strong valence band dispersion and a large bandgap. In order to evaluate the performance of this oxide as a p-type semiconductor, we perform first-principles calculations of the phonon-limited room-temperature carrier mobilities in SnO, SnO2, and Ta2SnO6. Electron relaxation time is evaluated, accounting for the scatterings from acoustic deformation potentials and polar optical phonons (POP), within the isotropic and dispersionless approximation. At room temperature, the electron/hole mobilities in a given material (SnO, SnO2, and Ta2SnO6) are found to be limited by POP scattering. SnO2 shows high room-temperature electron mobility of 192 cm2/(V s), while SnO and Ta2SnO6 exhibit impressive hole mobilities, with the upper limit at 60 and 33 cm2/(V s), respectively. We find that carrier effective mass largely accounts for the differences in mobility between these oxides with correspondingly different POP scattering rates. The theoretically predicted intrinsic mobilities of each material will provide the upper limit to the real mobilities for their device applications. Our findings also suggest a necessity of further investigation to identify even higher mobility p-type oxides with smaller hole effective masses. [ABSTRACT FROM AUTHOR]

The development of high-performance p-type oxides with high hole mobility and a wide bandgap is critical for the applications of metal oxide semiconductors in vertically integrated CMOS devices [Salahuddin et al., Nat. Electron. 1, 442 (2018)]. Sn2+-based oxides such as SnO and K2Sn2O3 have recently been proposed as high-mobility p-type oxides due to their relatively low effective hole masses, which result from delocalized Sn s-orbital character at the valence band edge. Here, we introduce a promising ternary Sn-O-X compound, Ta2SnO6, which exhibits strong valence band dispersion and a large bandgap. In order to evaluate the performance of this oxide as a p-type semiconductor, we perform first-principles calculations of the phonon-limited room-temperature carrier mobilities in SnO, SnO2, and Ta2SnO6. Electron relaxation time is evaluated, accounting for the scatterings from acoustic deformation potentials and polar optical phonons (POP), within the isotropic and dispersionless approximation. At room temperature, the electron/hole mobilities in a given material (SnO, SnO2, and Ta2SnO6) are found to be limited by POP scattering. SnO2 shows high room-temperature electron mobility of 192 cm2/(V s), while SnO and Ta2SnO6 exhibit impressive hole mobilities, with the upper limit at 60 and 33 cm2/(V s), respectively. We find that carrier effective mass largely accounts for the differences in mobility between these oxides with correspondingly different POP scattering rates. The theoretically predicted intrinsic mobilities of each material will provide the upper limit to the real mobilities for their device applications. Our findings also suggest a necessity of further investigation to identify even higher mobility p-type oxides with smaller hole effective masses. [ABSTRACT FROM AUTHOR]

Luminescence quenching in the presence of polarons is one of the major challenges in organic light emitting devices. In this work, exciton quenching in the presence of polarons is studied using phase sensitive photocurrent measurements on pentacene field effect transistors. The enhancement of conduction in the organic field effect transistors on light illumination is studied using photocurrent spectral response measurements and corresponding optical simulations. The photocurrent is shown to be governed by the polaron mobility and the exciton quenching efficiency, both of which depend on the polaron density in the channel. Two models are proposed on the exciton dynamics in the presence of gate induced polarons in the transistor channel. The first model simulates the steady-state exciton concentration profile in the presence of exciton-polaron interaction. The second one is a three-dimensional steady state exciton-polaron interaction model, which supports the findings from the first model. It is shown that the excitons quench by transferring its energy to polarons, thereby promoting the latter to high energy states in the density of states manifold. The polarons move in the higher energy states with greater microscopic mobility before thermalizing, thereby leading to an enhancement of conduction. It is observed that for the present system, where charge carrier transport is by hopping, all polarons interact with excitons. This implies that for low mobility systems, the interaction is not limited to deep trapped polarons. [ABSTRACT FROM AUTHOR]

The tin iodide-based hybrid perovskite (C6H5C2H4NH3)2SnI4 [(PEA)2SnI4] is promising as the semiconductor in field-effect transistors (FETs) because of its easy film processability and high carrier mobility. However, the stability of (PEA)2SnI4 FETs in air remains a significant issue. In this study, we show that the source of this degradation is oxygen. We observed that the structure of (PEA)2SnI4 degraded in the presence of oxygen, along with the formation of gaps between grains. With the aim of suppressing the oxygen-induced degradation, we optimized (PEA)2SnI4 spin-coating conditions to increase the grain size and simply encapsulated a (PEA)2SnI4 semiconductor with the fluorine-based polymer CYTOP. Adopting these methods led to the greatly improved stability of FET performance in air. We propose that oxygen had reduced penetration into (PEA)2SnI4 films with larger grains. The drain current of optimized FETs remained almost unchanged over 5 h of operation, which is in contrast to the control device that decayed within 1 h. [ABSTRACT FROM AUTHOR]