Semiconductor Charge Research Articles

High-accuracy current generation in the nanoampere regime from a silicon single-trap electron pump

A gigahertz single-electron (SE) pump with a semiconductor charge island is promising for a future quantum current standard. However, high-accuracy current in the nanoampere regime is still difficult to achieve because the performance of SE pumps tends to degrade significantly at frequencies exceeding 1 GHz. Here, we demonstrate robust SE pumping via a single-trap level in silicon up to 7.4 GHz, at which the pumping current exceeds 1 nA. An accuracy test with an uncertainty of about one part per million (ppm) reveals that the pumping current deviates from the ideal value by only about 20 ppm at the flattest part of the current plateau. This value is two orders of magnitude better than the best one reported in the nanoampere regime. In addition, the pumping accuracy is almost unchanged up to 7.4 GHz, probably due to strong electron confinement in the trap. These results indicate that trap-mediated SE pumping is promising for achieving the practical operation of the quantum current standard.

Fingerprints of Through-Bond and Through-Space Exciton and Charge π-Electron Delocalization in Linearly Extended [2.2]Paracyclophanes.

New stilbenoid and thiophenic compounds terminally functionalized with donor-donor, acceptor-acceptor, or donor-acceptor moieties and possessing a central [2.2]paracyclophane unit have been prepared, and their properties interpreted in terms of through-bond and through space π-electron delocalization (i.e., π-conjugations). Based on photophysical data, their excited-state properties have been described with a focus on the participation of the central [2.2]paracyclophane in competition with through-bond conjugation in the side arms. To this end, two-photon and one-photon absorption and emission spectroscopy, as a function of temperature, solvent polarity, and pressure in the solid state have been recorded. Furthermore, charge delocalization through the [2.2]paracyclophane in the neutral state and in the oxidized species (radical cations, dications and radical trications) has been investigated, allowing the elucidation of the vibrational Raman fingerprint of through-space charge delocalization. Thus, a complementary approach to both "intermolecular" excitation and charge delocalizations in [2.2]paracyclophane molecules is shown which can serve as models of charge and exciton migration in organic semiconductors.

ChemInform Abstract: Emerging Applications of Metal‐TCNQ Based Organic Semiconductor Charge Transfer Complexes for Catalysis

AbstractReview: 116 refs.

Modeling of Charge and Quantum Capacitance in Low Effective Mass III-V FinFETs

In this paper, we present a compact model for semiconductor charge and quantum capacitance in III-V channel FETs. With III-V being viewed as the most promising candidate for future technology node, a compact model is needed for their circuit simulation. The model presented in this paper addresses this need and is completely explicit and computationally efficient which makes it highly suitable for SPICE implementation. The proposed model is verified against the numerical solution of coupled Schrodinger–Poisson equation for FinFET with various channel thickness and effective mass.

Enhanced P3HT/ZnO Nanowire Array Solar Cells by Pyro-phototronic Effect.

The pyro-phototronic effect is based on the coupling among photoexcitation, pyroelectricity, and semiconductor charge transport in pyroelectric materials, which can be utilized to modulate photoexcited carriers to enhance the output performance of solar cells. Herein, we have demonstrated the largely enhanced output performance of a P3HT/ZnO nanowire array photovoltaic cell (PVC) by using the pyro-phototronic effect under weak light illuminations. By applying an external cooling temperature variation, the output current and voltage of the PVC can be dramatically enhanced by 18% and 152% under indoor light illumination, respectively. This study realizes the performance enhancement of pyroelectric semiconductor materials-based solar cells via a temperature-variation-induced pyro-phototronic effect, which may have potential applications in solar energy scavenging and self-powered sensor systems.

Conjugated Polymer Alignment: Synergisms Derived from Microfluidic Shear Design and UV Irradiation.

Solution shearing has attracted great interest for the fabrication of robust and reliable, high performance organic electronic devices, owing to applicability of the method to large area and continuous fabrication, as well as its propensity to enhance semiconductor charge transport characteristics. To date, effects of the design of the blade shear features (especially the microfluidic shear design) and the prospect of synergistically combining the shear approach with an alternate process strategy have not been investigated. Here, a generic thin film fabrication concept that enhanced conjugated polymer intermolecular alignment and aggregation, improved orientation (both nanoscale and long-range), and narrowed the π-π stacking distance is demonstrated for the first time. The impact of the design of shearing blade microfluidic channels and synergistic effects of fluid shearing design with concomitant irradiation strategies were demonstrated, enabling fabrication of polymer-based devices with requisite morphologies for a range of applications.

Number series of atoms, interatomic bonds and interface bonds defining zinc-blende nanocrystals as function of size, shape and surface orientation: Analytic tools to interpret solid state spectroscopy data

Semiconductor nanocrystals (NCs) experience stress and charge transfer by embedding materials or ligands and impurity atoms. In return, the environment of NCs experiences a NC stress response which may lead to matrix deformation and propagated strain. Up to now, there is no universal gauge to evaluate the stress impact on NCs and their response as a function of NC size dNC. I deduce geometrical number series as analytical tools to obtain the number of NC atoms NNC(dNC[i]), bonds between NC atoms Nbnd(dNC[i]) and interface bonds NIF(dNC[i]) for seven high symmetry zinc-blende (zb) NCs with low-index faceting: {001} cubes, {111} octahedra, {110} dodecahedra, {001}-{111} pyramids, {111} tetrahedra, {111}-{001} quatrodecahedra and {001}-{111} quadrodecahedra. The fundamental insights into NC structures revealed here allow for major advancements in data interpretation and understanding of zb- and diamond-lattice based nanomaterials. The analytical number series can serve as a standard procedure for stress evaluation in solid state spectroscopy due to their deterministic nature, easy use and general applicability over a wide range of spectroscopy methods as well as NC sizes, forms and materials.

Comparison of different rate constant expressions for the prediction of charge and energy transport in oligoacenes

Charge and exciton transport in organic semiconductors is crucial for a variety of optoelectronic applications. The prediction of the material‐dependent exciton diffusion length and the charge carrier mobility is a prerequisite for tailoring new materials for organic electronics. At room temperature often a hopping process can be assumed. In this work, three hopping models based on Fermi's Golden rule but with different levels of approximation—the spectral overlap approach, the Marcus theory, and the Levich–Jortner theory—are compared for the calculation of charge carrier mobilities and exciton diffusion lengths for oligoacenes, using the master equation approach and Monte Carlo simulations. WIREs Comput Mol Sci 2016, 6:694–720. doi: 10.1002/wcms.1273This article is categorized under: Structure and Mechanism > Computational Materials Science

Tunable capacitive coupling between two semiconductor charge qubits

Strong coupling between two qubits is one of the main requirements for high fidelity two-qubit logic operations. Here we experimentally investigate the capacitive coupling between two double quantum dots. A pair of open slot confinement gates is used to enhance the coupling. We find that the coupling energy J can be conveniently tuned in a broad range. Through numerical simulations, we study the effect of J on two-qubit operations. The analysis shows that our experimentally obtained J is adequate to achieve high fidelity two-qubit entanglement and logic gates.

ORGANIC DEVICES. Avoid the kinks when measuring mobility.

Transistor measurements can overstate organic semiconductor charge carrier mobility

Structure, Stoichiometry, and Charge Transfer in Cocrystals of Perylene with TCNQ-Fx

Semiconductor charge transfer (CT) cocrystals are an emerging class of molecular materials which combines the characteristics of the constituent molecules in order to tune physical properties. Cocrystals can exhibit polymorphism, but different stoichiometries of the donor–acceptor (DA) pair can also give different structures. In addition, the structures of the donor and acceptor as pristine compounds can influence the resulting cocrystal forms. We report a structural study on several CT cocrystals obtained by combining the polyaromatic hydrocarbon perylene with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its fluorinated derivatives having increasing electronegativity. This is achieved by varying the amount of fluorine substitution on the aromatic ring, with TCNQ-F2 and TCNQ-F4. We find structures with different stoichiometries. Namely, the system perylene:TCNQ-F0 is found with ratios 1:1 and 3:1, while the systems perylene:TCNQ-Fx (x = 2, 4) are found with ratios 1:1 and 3:2. We discuss the structures on ...

Interfacial charge transfer in a functionalized polyoxotitanate cluster

Understanding the charge transfer processes at the dye/TiO2 interface is often modeled using catechol/TiO2 systems. However, it indeed require precise structural information. In order to simulate the dye/TiO2 systems at a molecular level, herein we report the synthesis and structure of a novel titanium oxo-cluster [Ti4O(OiPr)6(DTBC)4] (1) functionalized with 3,5-di-tert-butylcatechol (DTBC). UV–Vis spectroscopy, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations show that 1 exhibits property of Ti(III) which is caused by substantial charge transfer from the π electrons of the benzene rings to Ti3d orbitals. The present precise structure and charge transfer mechanism help to better understand chromophore binding to semiconductor surfaces and charge transfer at the dye/TiO2 interfaces.

Emerging applications of metal-TCNQ based organic semiconductor charge transfer complexes for catalysis

7,7,8,8-tetracyanoquinodimethane (TCNQ), a strong electron withdrawing olefin, has long been regarded as an ideal compound for the synthesis of semiconducting coordination polymers when coordinated to transition metals. Given that TCNQ is an extremely good electron acceptor, transition metals such as Cu, Ag, Mn, Fe, Co, Ni, Zn and Cd have been surveyed for the synthesis of a variety of metal-TCNQ (MTCNQ) compounds. While each of these metal-organic charge transfer complexes show unique physico-chemical properties, these materials have been primarily investigated for electronics applications. More recently, the applicability of TCNQ class of nanomaterials has emerged in other important areas including catalysis, sensing and biology. In this review, the emerging applicability of MTCNQ complexes for catalysis is discussed. In particular, the fabrication of MTCNQ-based materials where M=Cu or Ag is surveyed, followed by discussion on improving their electron-hole recombination properties through a simple galvanic replacement reaction. The mechanistic aspect during the fabrication of these materials with an emphasis on their applicability in catalysis is outlined.

Transient Extraction of Holes and Electrons Separately Unveils the Transport Dynamics in Organic Photovoltaics

We have utilized the metal–insulator–semiconductor charge extraction by linearly increasing voltage (MIS‐CELIV) technique to clarify the hole‐ and electron‐transport properties in benchmark poly(3‐hexylthiophene) (P3HT) and its blend with phenyl‐C61‐butyric acid methyl ester (PCBM) by using a thick lithium fluoride (LiF) as the charge‐blocking layer. Both dark and light MIS‐CELIV are employed to comparatively investigate the differences in the recombination process and charge mobilities in neat P3HT and P3HT:PCBM blends. Our studies quantitatively show that balanced hole and electron transport can be achieved in the P3HT:PCBM blend under light illumination, leading to a high efficiency in the photovoltaic cell. Furthermore, light MIS‐CELIV can be employed as a novel method to directly evaluate the capability of photoelectric conversion of organic photovoltaic materials.

Enhanced electron-phonon coupling for a semiconductor charge qubit in a surface phonon cavity.

Electron-phonon coupling is a major decoherence mechanism, which often causes scattering and energy dissipation in semiconductor electronic systems. However, this electron-phonon coupling may be used in a positive way for reaching the strong or ultra-strong coupling regime in an acoustic version of the cavity quantum electrodynamic system. Here we propose and demonstrate a phonon cavity for surface acoustic waves, which is made of periodic metal fingers that constitute Bragg reflectors on a GaAs/AlGaAs heterostructure. Phonon band gap and cavity phonon modes are identified by frequency, time and spatially resolved measurements of the piezoelectric potential. Tunneling spectroscopy on a double quantum dot indicates the enhancement of phonon assisted transitions in a charge qubit. This encourages studying of acoustic cavity quantum electrodynamics with surface phonons.

Piezotronic Effect: An Emerging Mechanism for Sensing Applications.

Strain-induced polarization charges in a piezoelectric semiconductor effectively modulate the band structure near the interface and charge carrier transport. Fundamental investigation of the piezotronic effect has attracted broad interest, and various sensing applications have been demonstrated. This brief review discusses the fundamentals of the piezotronic effect, followed by a review highlighting important applications for strain sensors, pressure sensors, chemical sensors, photodetectors, humidity sensors and temperature sensors. Finally, the review offers some perspectives and outlook for this new field of multi-functional sensing enabled by the piezotronic effect.

Time-domain numerical modeling of terahertz receivers based on photoconductive antennas

We present here a simulator that solves the main semiconductor charge and transport equations coupled to Maxwell equations to study receivers based on photoconductive antennas (R-PCAs). Making use of this tool we were able to correctly characterize the operation of these antennas. In doing so, we compared simulations with the results of the semi-empirical expression ITHz(t)∝σc(t)*ETHz(t) employed to evaluate the detected photocurrent by means of the convolution between the photoconductivity in the receiver and the electric field linked to the emitter antenna. We were able to accurately reproduce experimental data with our simulation tool. These kinds of tools are essential to model photoconductive antennas, a fundamental step needed for the development of terahertz time-domain spectroscopy applications based on PCAs.

Electronic noise in charge sensitive preamplifiers for X-ray spectroscopy and the benefits of a SiC input JFET

A comprehensive summary and analysis of the electronic noise affecting the resolution of X-ray, γ-ray and particle counting spectroscopic systems which employ semiconductor detectors and charge sensitive preamplifiers is presented. The noise arising from the input transistor of the preamplifier and its contribution to the total noise is examined. A model for computing the noise arising from the front-end transistor is also presented and theoretical calculations comparing the noise contribution of transistors made of different materials are discussed, emphasizing the advantages of wide bandgap transistor technology.

Microwave Emission from Hybridized States in a Semiconductor Charge Qubit.

We explore the microwave radiation emitted from a biased double quantum dot due to the inelastic tunneling of single charges. Radiation is detected over a broad range of detuning configurations between the dot energy levels, with pronounced maxima occurring in resonance with a capacitively coupled transmission line resonator. The power emitted for forward and reverse resonant detuning is found to be in good agreement with a rate equation model, which considers the hybridization of the individual dot charge states.

Conditional rotation of two strongly coupled semiconductor charge qubits.

Universal multiple-qubit gates can be implemented by a set of universal single-qubit gates and any one kind of entangling two-qubit gate, such as a controlled-NOT gate. For semiconductor quantum dot qubits, two-qubit gate operations have so far only been demonstrated in individual electron spin-based quantum dot systems. Here we demonstrate the conditional rotation of two capacitively coupled charge qubits, each consisting of an electron confined in a GaAs/AlGaAs double quantum dot. Owing to the strong inter-qubit coupling strength, gate operations with a clock speed up to 6 GHz have been realized. A truth table measurement for controlled-NOT operation shows comparable fidelities to that of spin-based two-qubit gates, although phase coherence is not explicitly measured. Our results suggest that semiconductor charge qubits have a considerable potential for scalable quantum computing and may stimulate the use of long-range Coulomb interaction for coherent quantum control in other devices.