Geometric Diode Research Articles

Enhancing Backscattered Electron Detection in SEM: Investigating Geometric Collection Efficiency and Diode Layout Optimization

Enhancing Backscattered Electron Detection in SEM: Investigating Geometric Collection Efficiency and Diode Layout Optimization

Comprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects

Comprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects

A Graphene Geometric Diode with the Highest Asymmetry Ratio and Three States Gate‐Tunable Rectification Ability

AbstractGraphene geometric diodes, with applications in THz detection, energy harvesting, and high‐speed rectification, have been previously constrained by graphene quality and geometry feature size. This study presents significant advancements in graphene geometric diodes by employing the h‐BN/monolayer graphene/h‐BN heterojunction and extremely precise electron beam lithography. Two distinct designs of graphene geometric diodes with neck widths of 23 and 26 nm are fabricated, the superior of which demonstrated an asymmetry ratio of 1.97, a zero bias current responsivity of 0.6 A W−1, and a voltage responsivity of 12,000 V W−1, setting new benchmarks for such devices. Integrating this device into a rectification circuit, the experimentally validate that the rectified DC output voltage can be dynamically modulated and even inverted through adjustments to the diode's gate voltage. This behavior aligns seamlessly with graphene's intrinsic tunability of charge carriers, implying promising prospects for the device's application in advanced logic circuits, bidirectional switches, and signal modulation/demodulation techniques.

Omega‐Gate Silicon Nanowire Geometric Diodes with Reconfigurable Self‐Switching Operation and THz Rectification

AbstractGeometric diodes (GDs) represent a relatively unconventional class of diode that produces an asymmetric current response through carrier transport in an asymmetric geometry. Synthesized from the bottom up, Si nanowire‐based GDs are three‐dimensional, cylindrically symmetric nanoscale versions capable of room‐temperature rectification at GHz‐THz frequencies with near zero‐bias turn‐on voltages. Here, by fabricating three‐terminal n‐type Si nanowire GDs with axial contacts and an omega‐gate electrode, a distinct class of reconfigurable self‐switching geometric diodes (SSGDs) is reported. Single‐nanowire SSGD device measurements demonstrate a significant dependence of diode current and polarity on gate potential, where the diode polarity reverses at a gate potential of ≈−1 V under specific grounding conditions. Finite‐element modeling reproduces the experimental results and reveals that the gate potential—in combination with the morphology and dopant profile—produces an asymmetric potential along the nanowire axis that changes asymmetrically with axial bias, altering the effective conductive channel within the nanowire to yield diode behavior. The self‐switching effect is retained in two‐terminal SSGD devices, and modeling demonstrates that both three‐terminal and two‐terminal devices support rectification through THz frequencies. The results reveal a new mechanism of operation for nanowire‐based GDs and characterize a new type of self‐switching diode with reconfigurable polarity.

A full-wave time-dependent Schrödinger equation approach for the modeling of asymmetric transport in geometric diodes

Design and modeling of geometric diodes can be really challenging as it requires a rigorous quantum analysis at the nanoscale, accurate enough to capture the asymmetric behavior of charge transport. In this paper, we present a full-wave Time-Dependent Schrödinger Equation (TDSE) approach to model coherent transport in a two-dimensional geometric diode defined by an asymmetric taper of the domain where the charges are confined. The proposed solution clearly shows asymmetric transport, and provides a description of the rectification behavior in response to a parametric change. In general, the above model can account for even more complex geometries in order to optimize diodes performance.

Influence of Geometry on Quasi-Ballistic Behavior in Silicon Nanowire Geometric Diodes

Diodes are a basic component of electrical circuits to control the flow of charge, and geometric diodes (GDs) are a special class that can operate using ballistic or quasi-ballistic transport in conjunction with geometric asymmetry to direct charge carriers preferentially in one direction, enabling an electron ratcheting effect. Nanomaterials present a unique platform for the development of GDs, and silicon nanowire (NW)-based GDs─cylindrically symmetric but translationally asymmetric three-dimensional nanostructures─have recently been demonstrated functioning at room temperature. These devices can theoretically achieve a near zero-bias turn-on voltage and rectify up to THz frequencies. Here, we synthesize silicon NW GDs and fabricate single-NW devices from which significant changes in diode performance are observed from relatively minor changes in geometry. To elucidate the interplay between geometry and ballistic behavior, we develop a Monte Carlo simulation that describes the quasi-ballistic behavior of electrons within a three-dimensional NW GD. We examine the effects of doping level, temperature, and geometry on charge carrier transport, revealing the relationships between charge carrier mean free path (MFP), specular reflection at surfaces, and geometry on GD performance. As expected, geometry strongly influences performance by directing or blocking charge carrier passage through the nanostructure. Interestingly, we find that the blocking effect is at least as important as the directing effect. Moreover, within certain geometric limits, the diode behavior is less sensitive to the MFP than might be initially expected because of the short relevant length scales and importance of the blocking effect. The results provide guidelines for the future design of NW GDs and enable the prediction and interpretation of trends in experimental results. An improved understanding of quasi-ballistic transport is crucial to guiding future experiments toward realizing THz rectification for applications in high-speed data transfer and long-wavelength energy harvesting.

Wave-packet propagation in a graphene geometric diode

Dynamics of electron wave-packets is studied using the continuum Dirac model in a graphene geometric diode where the propagation of the wave packet is favored in certain direction due to the presence of geometric constraints. Clear rectification is obtained in the THz frequency range with the maximum rectification level of 3.25, which is in good agreement with recent experiments on graphene ballistic diodes. The rectification levels are considerably higher for systems with narrower channels. In this case, the wave packet transmission probabilities and rectification rate also strongly depend on the energy of the incident wave packet, as a result of the quantum nature of energy levels along such channels. These findings can be useful for fundamental understanding of the charge carrier dynamics in graphene geometry diodes.

A model for pumping optimization in edge-pumped disk amplifiers

A model for the calculation of the pump energy coupling to a disk amplifier is presented. The disk is considered to be pumped on its edge by diode bars. A composite geometry, namely a disk with a doped (pump absorbing) inner region surrounded by an undoped region is considered. The model allows the overall pump energy coupling as well as the absorption 3D map to be obtained for different geometric diode bars arrangements on an N-sided polygon. A set of fundamental conditions for the maximization of the total energy coupled to the active region is laid out first. Using the model, we then show that once these conditions are fulfilled, the precise diode bars arrangement and focusing can be tuned to get the desired energy absorption spatial distribution, while preserving the highest overall energy coupling to the doped region. The most interesting case of a cylindrically symmetric, radially uniform absorption profile is discussed, providing some general hints on achieving such a condition.

Current-Voltage Characterization of Multi-Port Graphene Based Geometric Diodes for High-Frequency Electromagnetic Harvesting

In this contribution, geometric diodes based on graphene patterned with spatial asymmetry have been studied, starting from tight-binding numerical approximation in a self-consistent framework, to verify their potential for electromagnetic (e. m.) harvesting. We report a detailed analysis of coherent charge transport and provide some figures of merit with respect to e. m. rectification, such as, for instance, the asymmetry of the dark current-voltage characteristics. The most important achievement of this work is given by the accurate analysis of the main key physical/geometric parameters that affect the nonlinear response of the diodes, for different configurations and geometries. Owing to the Scattering Matrix approach, introduced elsewhere for coherent transport calculation, it was possible to cascade asymmetric discontinuities and simulate large structures (more than 100K atoms) in a modular fashion. In this way, simulation at the atomistic level can be brought up to the device level to provide guidelines for design and fabrication, in view of practical applications related to clean-energy harvesting/rectification up to infrared and solar-light frequencies.

Wave-Packet Propagation in a Graphene Geometric Diode

Wave-Packet Propagation in a Graphene Geometric Diode

Wave-Packet Propagation in a Graphene Geometric Diode

Wave-Packet Propagation in a Graphene Geometric Diode

Asymmetric bias-induced barrier lowering as an alternative origin of current rectification in geometric diodes

Geometric diodes, which take advantage of geometric asymmetry to achieve current flow preference, are promising for THz current rectification. Previous studies relate geometric diodes’ rectification to quantum coherent or ballistic transport, which is fragile and critical of the high-quality transport system. Here we propose a different physical mechanism and demonstrate a robust current rectification originating from the asymmetric bias induced barrier lowering, which generally applies to common semiconductors in normal environments. Key factors to the diode’s rectification are carefully analyzed, and an intrinsic rectification ability at up to 1.1 THz is demonstrated.

Simulation of Z-Shaped Graphene Geometric Diodes Using Particle-in-Cell Monte Carlo Method in the Quasi-Ballistic Regime.

Geometric diodes are planar conductors patterned asymmetrically to provide electrical asymmetry, and they have exhibited high-frequency rectification in infrared rectennas. These devices function by ballistic or quasi-ballistic transport in which the transport characteristics are sensitive to the device geometry. Common methods for predicting device performance rely on the assumption of totally ballistic transport and neglect the effects of electron momentum relaxation. We present a particle-in-cell Monte Carlo simulation method that allows the prediction of the current–voltage characteristics of geometric diodes operating quasi-ballistically, with the mean-free-path length shorter than the critical device dimensions. With this simulation method, we analyze a new diode geometry made from graphene that shows an improvement in rectification capability over previous geometries. We find that the current rectification capability of a given geometry is optimized for a specific mean-free-path length, such that arbitrarily large mean-free-path lengths are not desirable. These results present a new avenue for understanding geometric effects in the quasi-ballistic regime and show that the relationship between device dimensions and the carrier mean-free-path length can be adjusted to optimize device performance.

CVD-Grown Monolayer Graphene-Based Geometric Diode for THz Rectennas.

For THz rectennas, ultra-fast diodes are required. While the metal–insulator–metal (MIM) diode has been investigated in recent years, it suffers from large resistance and capacitance, as well as a low cut-off frequency. Alternatively, a geometric diode can be used, which is more suitable due to its planar structure. However, there is only one report of a THz geometric diode based on a monolayer graphene. It is based on exfoliated graphene, and thus, it is not suitable for mass production. In this work, we demonstrate chemical vapor deposition (CVD)-grown monolayer graphene based geometric diodes, which are mass-producible. The diode’s performance has been studied experimentally by varying the neck widths from 250–50 nm, the latter being the smallest reported neck width for a graphene geometric diode. It was observed that by decreasing the neck widths, the diode parameters such as asymmetry, nonlinearity, zero-bias resistance, and responsivity increased within the range studied. For the 50 nm neck width diode, the asymmetry ratio was 1.40 for an applied voltage ranging from −2 V to 2 V, and the zero-bias responsivity was 0.0628 A/W. The performance of the diode was also verified through particle-in-cell Monte Carlo simulations, which showed that the simulated current-voltage characteristics were consistent with our experimental results.

Plasmonic analogue of geometric diodes realizing asymmetric optical transmission.

Geometric diodes represent a relatively new class of diodes used in rectennas that rely on the asymmetry of a conducting thin film. Here, we numerically investigate a plasmonic analogue of geometric diodes to realize nanoscale optical asymmetric transmission. The device operates based on spatial symmetry breaking that relies on a unique property of surface plasmon polaritons (SPPs), namely, adiabatic nanofocusing. We show that the structure can realize on-chip asymmetric electromagnetic transmission with a total dimension of ∼2µm×6µm. We demonstrate a signal contrast of 0.7 and an asymmetric optical transmission ratio of 4.77 dB. We investigate the origin of the asymmetric transmission and show that it is due mainly to asymmetric out-coupling of SPPs to far-field photons. We highlight the role of evanescent field coupling of SPPs in undermining the asymmetric transmission efficiency and show that by adjusting the plasmonic waveguide dimensions, a signal contrast of 0.94 and an asymmetric optical transmission ratio of 5.18 dB can be obtained. Our work presents a new paradigm for on-chip nanoscale asymmetric optical transmission utilizing the unique properties of SPPs.

Ratcheting quasi-ballistic electrons in silicon geometric diodes at room temperature.

Ratcheting effects play an important role in systems ranging from mechanical socket wrenches to biological motor proteins. The underlying principle is to convert a fluctuating, unbiased force into unidirectional motion. Here, we report the ratcheting of electrons at room temperature using a semiconductor nanowire with precisely engineered asymmetry. Modulation of the nanowire diameter creates a cylindrical sawtooth geometry with broken inversion symmetry on a nanometer-length scale. In a two-terminal device, this structure responded as a three-dimensional geometric diode that funnels electrons preferentially in one direction through specular reflection of quasi-ballistic electrons at the nanowire surface. The ratcheting effect causes charge rectification at frequencies exceeding 40 gigahertz, demonstrating the potential for applications such as high-speed data processing and long-wavelength energy harvesting.

Energy Harvesting Enhancement of Nanoantenna Coupled to Gemometric Diode Using Terhertz Transmitarray

This paper introduces the use of rhombus shaped dipole nanoantenna coupled to geometric diode in energy harvesting at 19.4 THz. An arc-shaped geometric diode is placed in the gap between the dipole arms. The diode I–V characteristics are investigated using the Monte Carlo simulation. Two approaches for enhancing the received voltage of nanoantenna energy harvesting at 19.4 THz are investigated. In the first approach, a terahertz transparent transmitarray is used to focus the electromagnetic waves on the surface of the nanoantenna coupled to the geometric diode. The received voltage is increased from 16.5 μV for single nanoantenna to 97.6 μV for the transmitarray coupled to the nanoantenna. In the second approach, Yagi nanoantenna arrangements are used to enhance the directivity of the single element and is coupled to the transmitarray.

Numerical Modeling of the Transport of Charged Particles in Graphene

Electronics for the detection of infrared or optical radiation are developing quite rapidly. The transformation of terahertz radiation into energy of electric current is an important problem in the search for promising new ways of converting the energy of solar and thermal radiation, designing new IR detectors, and other purposes. A geometric diode based on graphene is modeled as a rectifying element.

Nanoantenna with Geometric Diode for Energy Harvesting

A graphene based geometrical diodes coupled with nanoantennas for infrared (IR) energy harvesting has been introduced. The geometrical diode is an electronic device in which the current flow throug...

Nanoantenna with Geometric Diode for Energy Harvesting

A graphene based geometrical diodes coupled with nanoantennas for infrared (IR) energy harvesting has been introduced. The geometrical diode is an electronic device in which the current flow through it is controlled by its geometry. The I–V characteristics of the graphene based geometrical diodes are calculated by the Monte Carlo simulation. Different shapes of graphene geometrical diodes, arrowhead, modified staircase, and quarter-elliptical geometries have been examined. The equivalent impedance, capacitance, and responsitivity of each geometric diode have been calculated. The radiation characteristics of nanoantenna designed at 20.5 THz have been investigated. The IR harvesting using nanoantenna coupled with the graphene geometric diode has been calculated and interpreted. Full-wave simulation for the nanoantenna coupled to the geometric diode has been introduced. The DC voltage collected by the nanoantenna and rectified using the geometrical diode has been calculated.