Erping Li

Ab initio study of electronic and optical behavior of two-dimensional silicon carbide

Two-dimensional graphene-like silicon carbide (2d-SiC) has emerged as an intriguing new class of layered nanostructure. Using density functional theory, key electronic and optical properties of 2d-SiC nanosheets, in particular, of mono- and bilayer 2d-SiC, are investigated. The properties of these nanosheets are found to be highly dependent on their physical thickness and geometric configuration. Multilayer 2d-SiC exhibits an indirect bandgap. We find that monolayer 2d-SiC, on the other hand, has a direct bandgap (∼2.5 eV) that can be tuned through in-plane strain. We also show that the optical conductivity of multilayer 2d-SiC is sensitive to the interlayer spacing. The results suggest that unlike graphene, silicene and even multilayer 2d-SiC, monolayer 2d-SiC could be a good candidate for optoelectronic devices such as light-emitting diodes.

Unidirectional surface plasmons in nonreciprocal graphene

We demonstrate theoretically the existence of unidirectional surface plasmons in the nonreciprocal graphene-based gyrotropic interfaces. We show that a unidirectional frequency range is raised under a static external magnetic field where only one propagating direction is allowed for the surface plasmons mode. By efficiently controlling the chemical potential of graphene, the unidirectional working frequency can be continuously tunable from THz to near-infrared and even visible. Particularly, the unidirectional frequency bandwidth can be 1– 2 orders of magnitude larger than that in metal under the same magnetic field, which arises from the superiority of extremely small effective electron mass in graphene. Based on our theoretical analysis, two tunable graphene-based directional devices are proposed, showing the appealing properties of nonreciprocal graphene in the nonreciprocal optical devices design.

Modeling and Simulation of Graphene-Gated Graphene-GaAs Schottky Junction Field-Effect Solar Cell for Its Performance Enhancement

Modeling and simulation of graphene-gated graphene-GaAs Schottky junction field-effect solar cell is performed using in-house developed algorithm based on finite-difference method, where Poisson and drift-diffusion equations are solved in an appropriate way. Our algorithm is verified by comparing the simulated J-V curve of solar cell with the previous experimental one. The carrier generation rate is calculated with light multireflection in the solar cell excluded, due to large optical absorption coefficient of GaAs, and the radiative recombination in GaAs leads to ~5% light generated carrier loss. The charge transfer effect in graphene is investigated, which can affect open circuit voltage, and in particular for the semiconductor substrate with very low hole mobility. It is further numerically demonstrated that: (1) both open circuit voltage VOC and short circuit current JSC of the solar cell are governed by doping concentration through affecting Schottky barrier height and depletion width; (2) the value of VOC can be effectively adjusted by decreasing the thickness of gate oxide; however, it may result in oxide breakdown or reliability problem; and (3) there is tunability inertia for VOC with multilayer junction graphene implemented, but it can provide low series resistance.

Electrothermal Investigation on Vertically Aligned Single-Walled Carbon Nanotube Contacted Phase-Change Memory Array for 3-D ICs

Electrothermal investigation on vertically aligned single-walled carbon nanotube (SWCNT) contacted phase-change memory (PCM) array is performed using the 3-D time-domain finite-element method. The in-house-developed algorithm is verified by comparing the simulated results with the experimental ones published by others. Thermal coupling between adjacent cells, which may cause current leakage and reliability degradation, is characterized for PCMs with different geometrical parameters, which could be caused by fabrication variation. It is shown that spacing variation between adjacent PCM cells draws a slight effect on their thermal coupling. However, thermal boundary resistance of the phase-change material-oxide interface and SWCNT diameter affect temperature rise and thermal coupling significantly. On the other hand, it is indicated that the SWCNT contacted PCM has microampere-scale programming current and nanosecond-scale thermal response time, which make it vulnerable to electrostatic discharge (ESD). Electrothermal responses to ESD are captured and compared, which show that unintentional ESD can change the state of PCM and result in error programming.

Reconfigurable Parallel Plasmonic Transmission Lines With Nanometer Light Localization and Long Propagation Distance

A hybrid plasmonic parallel transmission line scheme constructed by a spatial single mode with time-domain multiline waveguide is presented in this paper. The proposed configuration enables a nanometer light localization while retaining a long propagation distance (~74 μm) at optical communication wavelengths with no crosstalk between data channels. High extinction ratio between the nanoribs peak energies (~20 dB) has been achieved after optimization. Furthermore, the proposed optical parallel transmission line scheme shows the advantages of enabling an optical device with a large number of parallel transmission channels, as well as a good robustness with respect to the fabrication tolerances.

Toroidal Localized Spoof Plasmons on Compact Metadisks

Abstract Localized spoof surface plasmons (LSSPs) have recently emerged as a new research frontier due to their unique properties and increasing applications. Despite the importance, most of the current researches only focus on electric/magnetic LSSPs. Very recent research has revealed that toroidal LSSPs, LSSPs modes with multipole toroidal moments, can be achieved at a point defect in a 2D groove metal array. However, this metamaterial shows the limitations of large volume and poor compatibility to photonic integrated circuits. To overcome the above challenges, here it is proposed and experimentally demonstrated compact planar metadisks based on split ring resonators to support the toroidal LSSPs at microwave frequencies. Additionally, it is experimentally demonstrated that the toroidal LSSPs resonance is very sensitive to the structure changes and the background medium. These might facilitate its utilization in the design and application of plasmonic deformation sensors and the refractive index sensors.

A Low-Profile Broadband Bandpass Frequency Selective Surface With Two Rapid Band Edges for 5G Near-Field Applications

A low-profile broadband bandpass frequency selective surface (FSS) with two rapid band edges is proposed in this paper for 5G near-field applications. The overall structure consists of three metallic layers, separated by two thin substrates with a thickness of 0.07λ. In addition, some centro-symmetric miniaturized slots are introduced in the middle metallic layer to further improve its stability and reduce its physical dimensions. A corresponding equivalent circuit model (ECM) is also proposed to better analyze the principles of the proposed FSS. Finally, an FSS prototype working at the center frequency of 27.5 GHz with a relative −3 dB bandwidth of 20.5% is fabricated and measured. More than 25 dB shielding effectiveness can be obtained out of the passband for a bandwidth of 1.46 GHz in this experiment. Both 3-D full-wave simulations and ECM results are in good agreement with the experimental results, having a maximum deviation of only 2.257% in the transmission zeros and poles. These results demonstrate that the proposed FSS is a good candidate for 5G near-field EMI shielding.

Graphene-silicon diode loaded patch antenna

In this paper, we proposed a graphene-silicon diode loaded patch antenna, which is fabricated on silicon wafer. The structure of patch antenna is perfectly compatible with the diode process. Its equivalent circuit and frequency-tunable characteristics are analyzed with an equivalent circuit model. The result is verified by 3-D full-wave simulation. This patch antenna, which is directly printed on silicon wafer, finds a potential application of graphene in GHz frequency band and can be easily integrated with other integrated circuits.