Metal oxide-based electronics is advancing rapidly where the reduced dimensions require transistor structures different to conventional CPUs. The double injection function transistor (DIFT) is a type of a source-controlled transistor. As doping is a facile method in the semiconductor industry, we suggest that the DIFT can be realized through a doping pattern under the source electrode. We show that double doping functions similarly to the double work function DIFT, recently demonstrated. We use device simulations to analyze the operation principle of the DIFT structure and provide design guidelines. We find that the structural separation of the injection and depletion functions allows adapting the transistor structure to fabrication process limitations. A 200 nm channel length InGaZnO based device can be designed to exhibit proper saturation at sub-1 V drain bias.

We propose and demonstrate self-aligned Double Injection Function Thin Film Transistor (DIF-TFT) architecture that mitigates short channel effects in 200 nm channel on non-scaled insulator (100 nm SiO₂). In this conceptual design, a combination of ohmic-like injection contact and a high injection-barrier metal allows maintaining the high on currents while suppressing drain-induced barrier lowering (DIBL) effects. Using an industrial 2-D device simulator (Sentaurus), we propose two methods to realize the DIF concept. We use one of them to demonstrate, experimentally, a DIF-TFT based on solution-processed indium gallium zinc oxide (IGZO). Using molybdenum as the ohmic contact and platinum as the high injection barrier, we compare three transistors' source-contacts: ohmic, Schottky, and DIF. The fabricated DIF-TFT exhibits saturation at sub 1 V drain bias with only about a factor of 2 loss in on current compared to the ohmic contact.

The low carrier mobility of organic semiconductors and the high parasitic resistance and capacitance often encountered in conventional organic Schottky diodes, hinder their deployment in emerging radio frequency (RF) electronics. Here we overcome these limitations by combining self-aligned asymmetric nanogap electrodes (∼25 nm) produced by adhesion-lithography, with a high mobility organic semiconductor and demonstrate RF Schottky diodes able to operate in the 5G frequency spectrum. We used C₁₆IDT-BT, as the high hole mobility polymer, and studied the impact of p-doping on the diode performance. Pristine C₁₆IDT-BT-based diodes exhibit maximum intrinsic and extrinsic cutoff frequencies (f_C) of >100 and 6 GHz, respectively. This extraordinary performance is attributed primarily to the planar nature of the nanogap channel and the diode's small junction capacitance (< 2 pF). Doping of C₁₆IDT-BT with the molecular p-dopant C₆₀F₄₈, improves the diode's performance further by reducing the series resistance resulting to intrinsic and extrinsic f_C of >100 and ∼14 GHz respectively, while the DC output voltage of a RF rectifier circuit increases by a tenfold. Our work highlights the importance of the planar nanogap architecture and paves the way for the use of organic Schottky diodes in large-area radio frequency electronics of the future.

Magnetic field and temperature dependence of the magneto-conductance (MC) of thin films made of self-p-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) having room temperature conductivity of ≈200 S cm⁻¹ in the range of fields B = 0–14 T and temperatures T = 1.8–300 K are reported. At B = 0 and for current parallel to the film surface, the conductance follows a variable range hopping mechanism in two dimensions. It is shown that the finite Coulomb correlations, U, within the nano-crystalline PEDOT islands dominates MC at low temperatures and high fields. At T = 1.8 K, the intra-island Coulomb correlation spin polarization mechanism is already saturated for B > 10 T establishing a finite minimum of ≈2 meV for U. This small value of U is in line with the delocalized nature of the holes within the PEDOT islands and the relatively high conductivity that makes it essential in organic opto-electronics.

Theoretical studies of ion migration have thus far focused on migration within the perovskite layer only. This reflected a “hidden” assumption that the electron/hole blocking layers also function as ion blocking. Following experimental evidence, we study the effect of ion migration into the blocking layers and as a case study we compare our simulations to experimental results of device degradation under storage conditions (V = 0, dark), obtained by others. Good agreement is found between the simulated ion accumulation at the electrode interface with the experimental device degradation dynamics. Also, we find that the migration into the blocking layers dominates the effects on the device energy level diagram and that it may also turn the intrinsic perovskites into either p or n type solar cells. Although our simulations do not include the chemistry of degradation, they show two potential mechanisms associated with ion out-diffusion. First, the electron/hole balanced solar cell structure becomes imbalanced (should be reversible). Second, ions reaching the electrode may react with it (i.e. irreversible).

Robust control over the carrier type is fundamental for the fabrication of nanocrystal‐based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals (NCs), post‐synthetically doped with Cd, serve as a model system for successful p‐type doping of originally n‐type InAs nanocrystals, as demonstrated in field effect transistors (FETs). Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X‐ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p‐dopants replacing Indium. Commensurately, Cd‐doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declines. Therefore, Cd plays a dual role acting as a p‐type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X‐ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd‐doped InAs NCs films. This study demonstrates robust p‐type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices.

Two derivatives of [1]benzothieno[3,2-b][1]benzothiophene (BTBT), namely, 2,7-dioctyl-BTBT (C8-BTBT) and 2,7-diphenyl-BTBT (DPh-BTBT), belonging to one of the best performing organic semiconductor (OSC) families, have been employed to investigate the influence of the substitutional side groups on the properties of the interface created when they are in contact with dopant molecules. As a molecular p-dopant, the fluorinated fullerene C₆₀F₄₈ is used because of its adequate electronic levels and its bulky molecular structure. Despite the dissimilarity introduced by the OSC film termination, dopant thin films grown on top adopt the same (111)-oriented FCC crystalline structure in the two cases. However, the early stage distribution of the dopant on each OSC film surface is dramatically influenced by the group side, leading to distinct host–dopant interfacial morphologies that strongly affect the nanoscale local work function. In this context, Kelvin probe force microscopy and photoelectron emission spectroscopy provide a comprehensive picture of the interfacial electronic properties. The extent of charge transfer and energy level alignment between OSCs and dopant are debated in light of the differences in the ionization potential of the OSC in the films, the interface nanomorphology, and the electronic coupling with the substrate.

Ion migration into blocking layers toward the metallic electrodes is studied within a semiconductor device model framework. We find that ion leakage into the blocking layers and their accumulation at the electrode interface are significantly affected by the electronic injection barrier at the contact. Specifically, we find that if the device structure promotes, under light, hole (electron) accumulation within the perovskite layer, these excess holes (electrons) would release an almost equivalent number of cations (anions) into the transport layers toward the contacts. Our analysis suggests that it would be beneficial to include intentional doping of the blocking layers and that it should follow the “just enough” strategy.

We provide experimental and theoretical understanding on fundamental processes taking place at room temperature when a fluorinated fullerene dopant gets close to a metal surface. By employing scanning tunneling microscopy and photoelectron spectroscopies, we demonstrate that the on-surface integrity of C₆₀F₄₈ depends on the interaction with the particular metal it approaches. Whereas on Au(111) the molecule preserves its chemical structure, on more reactive surfaces such as Cu(111) and Ni(111), molecules interacting with the bare metal surface lose the halogen atoms and transform to C₆₀. Though fluorine–metal bonding can be detected depending on the molecular surface density, no ordered fluorine structures are observed. We show the implications of the metal-dependent de-fluorination in the electronic structure of the molecules and the energy alignment at the molecule–metal interface. Molecular dynamics simulations with ReaxFF reactive force field corroborate the experimental facts and provide a detailed mechanistic picture of the surface-induced de-fluorination, which involves the rotation of the molecule on the surface. Outstandingly, a thermodynamic analysis indicates that the effect of the metal surface is lowering and diminishing the energy barrier for C–F cleave, demonstrating the catalytic role of the surface. The present study contributes to in-depth knowledge of the mechanisms that affect the degree of stability of chemical species on surfaces, which is essential to advance our understanding of the chemical reactivity of metals and their role in on-surface chemical reactions.

The use of ternary systems comprising polymers, small molecules, and molecular dopants represents a promising approach for the development of high-mobility, solution-processed organic transistors. However, the current understanding of the charge transport in these complex systems, and particularly the role of molecular doping, is rather limited. Here, the role of the individual components in enhancing hole transport in the best-performing ternary blend systems comprising the small molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C₈-BTBT), the conjugated polymer indacenodithiophene-alt-benzothiadiazole (C₁₆IDT-BT), and the molecular p-type dopant (C₆₀F₄₈) is investigated. Temperature-dependent charge transport measurements reveal different charge transport regimes depending on the blend composition, crossing from a thermally activated to a band-like behavior. Using the charge-modulation spectroscopy technique, it is shown that in the case of the pristine blend, holes relax onto the conjugated polymer phase where shallow traps dominate carrier transport. Addition of a small amount of C₆₀F₄₈ deactivates those shallow traps allowing for a higher degree of hole delocalization within the highly crystalline C₈-BTBT domains located on the upper surface of the blend film. Such synergistic effect of a highly ordered C₈-BTBT phase, a polymer bridging grain boundaries, and p-doping results in the exceptionally high hole mobilities and band-like transport observed in this blend system.