Optoelectronic Conversion Research Articles

FPGA based Quantum Key Distribution Electronic System for Multipurpose Optical Setup and Protocols

The purpose of the FPGA electronic control system for Quantum Key Distribution (QKD) is to improve the analog electronic system in optoelectronic conversion. In the existence of the Mezzanine FPGA board, the main conversion of optical laser signal and optical detector signal can be improved. Mezzanine board can reduce the noise errors during the transmission and receiving a signal. Commonly, the optical signal needs to interface with an analog electronic system. This process requires the conversion process and interfacing with a digital signal to control the optical device and produce a good quality optical signal. The Mezzanine board can reduce the uncertainty during signal conversion and gives the digital capability to control the optical devices. The optical modulation signal for phase modulator control can achieve a full complete phase shift in the Mezzanine board. Plus, the voltage phase has capability up to 10 V with an accuracy of 2.4 µV. The time conversion for phase modulator can be extended in the Mezzanine board based on the digital control signal from FPGA. The system is capable to extend into multiple timing control to handle all the signal and to synchronize the signal in receiving, transmission or in between of the transmission. Thus, the system can handle one way or two-way QKD system accordingly.

Research on ultra-wideband and high saturation power uni-traveling carrier photodetectors (Invited)

Ultra-wideband uni-traveling carrier (UTC) photodetectors have broadband advantages over traditional PIN detectors, as only fast electrons are required to transport in UTC photodetectors. They will be one of the key optoelectronic devices in the sub-terahertz systems, such as 6G broadband wireless communications, terahertz imaging, ultra-wideband noise generators, etc. For the requirements of optoelectronic conversion in sub-terahertz frequency band, high-speed photo-generated carrier transport mechanics and inductive coplanar waveguide (CPW) structure were studied to improve the device bandwidth and saturation power of the photodetector. A dual-drift layer structure MUTC photodetector chip with bandwidth of 106 GHz, saturated output power of 7.3 dBm, and a CPW-optimized MUTC photodetector chip with bandwidth over 150 GHz were developed.

Hot-carrier enhanced light emission: The origin of above-threshold photons from electrically driven plasmonic tunnel junctions

Understanding the origin of above-threshold photons emitted from electrically driven tunnel junctions (ℏω>eVb with Vb being the applied voltage bias) is of current interest in nano-optics and holds great promise to create novel on-chip optoelectronic and energy conversion technologies. Here, we report experimental observation and theoretical analysis of above-threshold light emission from electromigrated Au tunnel junctions. We compare our proposed hot-carrier enhanced light emission theory with existing models, including blackbody thermal radiation, multi-electron interactions, and an interpretation involving finite temperature effects. Our study highlights the key role of plasmon-induced hot carrier dynamics in emitting above-threshold photons and the need to further explore the underlying mechanisms and optimization of upconversion effects in plasmonically active nanostructures.

Preparation and properties of optoelectronic conversion films of perovskite modified by octadecyl-trichloro silane

• A simple and effective antisolvent strategy to improve the quality of perovskite film. • Octadecyl-trichloro silane (OTS) was introduced to improve crystallization and stability. • The performance of OTS modified perovskite solar cells has been greatly improved and got a PCE of 19.89%.

Structural optimization of optoelectronic components in millimeter-wave radio-transmitting modules

The paper analyzes the effect of structure inherent to optoelectronic radio-transmitting modules of a phased array antenna (PAA) on the noise characteristics in the millimeter range (MMR) of waves. Considered are promising structures of MMR modules for generating radiation with a phased array for communication systems based on optoelectronic technologies. The promising types of photodiodes that are used to form MMR radio signals as well as the distance and physical limitations for photodetectors associated with a limited bandwidth and nonlinear response characteristics have been analyzed. Mathematical modeling of the oscillation of the output current after the optoelectronic conversion of the signal and noise characteristics of the radio-transmitting modules capable to form MMR radiation in PAA has been carried out. The analysis of the nonlinearity of the sensitivity of photodiodes in the high-frequency regions of formation of radio signals has been carried out. The necessity to structurally optimize optoelectronic components in the MMR transmission module has been shown depending on the noise characteristics of the output signal. It has been shown that fundamental studies of nonlinear characteristics and factors limiting the band of photodetectors are important tasks for further developing MMR telecommunications of the next generations.

Novel thieno-imidazole salt-based hole transport material for dopant-free, efficient inverted perovskite solar cell applications

A unique quaternary iodide salt of thieno-imidazole, AI110, is designed, prepared and tested on an inverted (p-i-n) architecture perovskite solar cell (PSC) as a dopant-free hole transport material (HTM). The opto-electronic and power conversion properties of this novel aryl salt HTM are well characterized. The inverted PSC based on AI110 without any dopants and additional interlayers using the simplest device structure affords the best efficiency of 14.90%, which is much higher than those of the most widely used HTMs, Spiro-OMeTAD (11.84%) and PEDOT:PSS (12.55%). The superior performance of the aryl salt AI110 HTM is due to its significant capabilities of film formation, charge extraction, and hole mobilities which result in reducing current loses and charge recombination and thus increasing power conversion.

Dynamic Filtering of Microwave Signals Through Brillouin-Based Polarization-Sensitive Balanced Detection

A new photonic technique to implement both stopband and passband microwave filters is presented and demonstrated. The principle of operation relies on controlling the state of polarization of the band of interest using stimulated Brillouin scattering-based polarization rotation and the optoelectronic conversion of this polarization-structured signal by means of a polarization sensitive balanced photodetection. Using the proposed architecture, the filter response can be dynamically switched to implement a stopband or a passband response with the same scheme, thus enhancing its flexibility and application potential. Experiments with a single stage show that very high stopband rejection can be implemented, 67 dB, which for the best of our knowledge is the highest stopband rejection for a photonic microwave notch filter reported to date. Measurements also show that the filter response can be dynamically changed to implement a bandpass response.

Structures, properties and application of 2D monoelemental materials (Xenes) as graphene analogues under defect engineering

• As graphene analogues, 2D monoelemental materials composed of elements from the group-IIIA to the group-VIA have rich and unique electronic and optical properties similar to and different from graphene. • As a method that is easy to be introduced experimentally, defect doping is also used to effectively regulate the electronic and optical properties of the system in the simulation calculation of materials. • Intrinsic defects as an inevitable means in the process of experiment and external defects as an artificial controllable control means, all of them have significant influence on the properties of single element two-dimensional materials, whether these systems are based on experimental or theoretical calculations. • Defective 2D Xenes materials excellent optoelectronic properties, so they have profound applications in optoelectronic devices, energy storage and conversion and catalysis. They are also expected to play positive and important role in many other fields. From the group-IIIA (borophene), to the group-IVA (silicene, germanene and stanine), as well as the group-VA (phosphorene, arsenene, antimonene and bismuthene) and even the group-VIA (selenene and tellurene nanosheets), these two-dimensional (2D) monoelemental materials are highly similar to graphene in lattice structure, and they can also be collectively referred to as Xenes. However, the unique specific atomic arrangement of these materials gives rise to a vast diversity of properties, and these single element 2D materials as graphene analogues are the most chemically tractable materials for synthetic exploration, thus attracting widespread attention and research. Intrinsic defects, as an defects inevitably introduced in the of experimental preparation, and extrinsic defects, as an artificially introduced and controllable way, both of them can effectively improve the environmental stability of single element materials and regulate the properties of Xenes. Herein, a review of the historical work about the properties and application of defective 2D monoelemental materials is presented. Based on the structure and properties of original single element 2D materials, the change of electronic and optoelectronic properties of these materials from different main groups under the action of different defects are classified and compared. In addition, the existing methods of realizing defects of 2D Xenes-based materials are summarized, and the application of the defects engineering in the field of optoelectronic devices, energy storage and conversion, catalysts as well are also comprehensively searched and reviewed. Finally, this review provides the prospect and challenge for the preparation and application of defective 2D monoelemental materials on the basis of the current research and development.

Design of Micro-ring Resonator Based 4 × 4 Optical Router for Photonic Network Applications

A 4 × 4 optical router which is composed of only four micro-ring resonator based switching elements is designed without any need of optoelectronic conversion for use in integrated optical networks. The geometrical structure including the number of rings and waveguide junctions are optimized through numerical simulation, which minimizes the crosstalk and the transmission loss and improves the loss of different paths of the optical router. The design can route four optical single-wavelength input signals to any of the four output ports and provided extinction ratio larger than 14 dB for all available optical paths. The average switching power consumption is about 1.2 mW per ring. The routing functionality and optical signal reliability are confirmed through numerical simulation.

Structural, electronic, and optical properties of ZnO:ZnSnN2 compounds for optoelectronics and photocatalyst applications

Semiconductors with suitable band gap are highly desirable for the applications in optoelectronic and energy conversion devices. In this work, using the recently developed strongly constrained and appropriately normed (SCAN) density functional calculations in conjunction with hybrid functional, we investigate the structural, electronic, and optical properties of earth abundant element based ZnO:ZnSnN2 compounds formed through alloying. The proposed ZnO:ZnSnN2 compounds in the low energy configurations possess band gaps of 2.28 eV-2.52 eV. The decrease in band gap compared to ZnO is mainly attributed to the p-d repulsion between N 2p+O 2p and Zn 3d electrons that lifts the top of valence band. For the ZnO:ZnSnN2 compounds studied the band edges straddle the water redox potentials and the absorption onsets lie in the visible light range. Our studies are helpful for ZnO:ZnSnN2 compounds' experimental synthesis and future application in optoelectronics and photocatalyst.

3D anisotropic photocatalytic architectures as bioactive nerve guidance conduits for peripheral neural regeneration

Great research efforts have been invested in developing nerve guidance conduits (NGCs), which can direct axons advance and guide peripheral neural regeneration. Here, three different aspects of NGC design, namely anisotropy, photocatalytic stimulation and self-assembly at implantation site, were unitedly addressed. Firstly, melt electrowriting (MEW) was used to print anisotropic, microfibrous PCL architectures. Specifically, by tailoring the fiber spacing ratio between two arms of the grid patterns (1-1, 1–2, 1–3), preferential neurite extension of PC 12 cells along the long arm direction was achieved. Such anisotropic neurites guidance was further strengthened when the intersection angles were reduced from 90° to 30°. Secondly, functionalization of PCL micropatterns with graphene oxide and graphitic carbon nitride (g-C3N4), a visible-light photocatalyst, may enable optoelectronic conversion and wireless neural stimulation. As a result, photocatalytic stimulation further enhanced neurite extension length under visible light irradiation. Last but not the least, NGC were successfully obtained either by manually rolling or self-assembly using a thermo-responsive bi-layer system. Interestingly, the anisotropic micropattern design dictated the self-assembly process, and an underlying mechanism was proposed. With a synergy of three unique design parameters, the herein presented NGCs may possess great potential for repairing peripheral nerve injuries.

Enabling Efficient Charge Separation for Optoelectronic Conversion via an Energy-Dependent Z-Scheme n-Semiconductor-Metal-p-Semiconductor Schottky Heterojunction.

Achieving good charge separation while maintaining energetic electronic states in heterostructures is a challenge in designing efficient photocatalyst materials. Using first-principles calculations, we propose a Z-scheme Sn-m-Sp (n-semiconductor-metal-p-semiconductor) heterojunction as a viable avenue for achieving broad-spectrum sunlight absorption and, importantly, energy-dependent charge separation. As a proof-of-concept investigation, we investigated two ternary heterostructures, CdS-Au-PdO and SnO2-W-Ag2O, in which the electronic Fermi levels line up by virtue of the presence of an intermediate metal layer. A cascade of work functions in the relative order Wn < Wm < Wp drives electrons flowing from Sn to m and from m to Sp. The inner electric fields established at the Sn-m and m-Sp Schottky junctions selectively guide low-energy photoexcited electrons from Sn (CdS/SnO2) and low-energy holes from Sp (PdO/Ag2O) to the interposing Au or W metal, respectively. Importantly, relatively low Schottky barriers enforce charge separation by constraining high-energy photogenerated charges to the individual semiconductor layers. Operating together, these two mechanisms enable the achievement of highly efficient optoelectronic conversion.

Single-crystal synthesis and properties of the open-framework allotrope Si24

Si24 is a new, open-framework silicon allotrope that is metastable at ambient conditions. Unlike diamond cubic silicon, which is an indirect-gap semiconductor, Si24 has a quasidirect gap near 1.4 eV, presenting new opportunities for optoelectronic and solar energy conversion devices. Previous studies indicate that Na can diffuse from micron-sized grains of a high-pressure Na4Si24 precursor to create Si24 powders at ambient conditions. Remarkably, we demonstrate here that Na remains highly mobile within large (~100 µm) Na4Si24 single crystals. Na readily diffuses out of Na4Si24 crystals under vacuum with gentle heating (10−4 mbar at 125 °C) and can be further reacted with iodine to produce large Si24 crystals that are 99.9985 at% silicon, as measured by wavelength-dispersive x-ray spectroscopy. Si24 crystals display a sharp, direct optical absorption edge at 1.51(1) eV with an absorption coefficient near the band edge that is demonstrably greater than diamond cubic silicon. Temperature-dependent electrical transport measurements confirm the removal of Na from metallic Na4Si24 to render single-crystalline semiconducting samples of Si24. These optical and electrical measurements provide insights into key parameters such as the electron donor impurity level from residual Na, reduced electron mass, and electron relaxation time. Effective Na removal on bulk length scales and the high absorption coefficient of single-crystal Si24 indicate promise for use of this material in bulk and thin film forms with potential applications in optoelectronic technologies.

Planar ultrathin omni-directional perfect absorber utilizing amorphous silicon for photovoltaics

Resonant plasmonic metasurfaces and thin film stacks have been extensively studied for spectral control and perfect absorption enhancement functionality. Essentially, the plasmonic nanostructures or metallic films enable the optical field resonant and confinement at the nanoscale, and thus yield the Ohmic heat absorption in the nanoscale metals. However, typical perfect absorbers based on film coatings are usually sensitive to the variation of large oblique incident angles, and mostly lack the capability for direct conversion to photocurrents and photovoltaics. Here, we proposed a lithography-free perfect absorber design consisting of metallic and amorphous silicon (α-Si) films with deep-subwavelength thickness (∼ λ/20 - λ/100). The perfect absorptivity spectrum enjoys Omni-directional optical characteristics, which remains the high absorption for the normal incidence to large oblique incidence angles of ± 60°. Due to the strongly trapped resonance in the Fabry-Perot cavity, the majority of light absorption (∼89%) takes place in the core α-Si layer, which could enable the potential optoelectronic conversion to photocurrents and photovoltaics. Our proposed perfect absorber based on ultrathin α-Si films enjoys the great simplicity of design and manufacturing and suggests a variety of promising applications, including photovoltaics, optical sensors, solar cells, photodetectors, thermal bolometers, nano-imaging devices, color filters, and thermal emitters, etc.

Imaging of the Atomic Structure of All-Inorganic Halide Perovskites.

All-inorganic halide perovskites are promising materials for optoelectronic applications. The surface or interface structure of the perovskites plays a crucial role in determining the optoelectronic conversion efficiency, as well as the material stability. A thorough understanding of surface atomic structures of the inorganic perovskites and their contributions to their optoelectronic properties and stability is lacking. Here we show a scanning tunneling microscopy investigation on the atomic and electronic structure of CsPbBr3 perovskite. Two different surface structures with a stripe and an armchair domain are identified, which originates from a complex interplay between Cs cations and Br anions. Our findings are further supported and correlated with density functional theory calculations and photoemission spectroscopy measurements. The stability evaluation of photovoltaic devices indicates a higher stability for CsPbBr3 in comparison with MAPbBr3, which is closely related to the low volatility of Cs from the perovskite surface.

Near-unity photoluminescence quantum yield in inorganic perovskite nanocrystals by metal-ion doping.

The luminescence and charge transport properties of inorganic CsPbX3 perovskite nanocrystals (NCs) make them attractive candidates for various optoelectronic applications, such as lasing, X-ray imaging, light communication, and light-emitting diodes (LEDs). However, to realize cutting-edge device performance, high-quality NCs with high photoluminescence quantum yields (PLQYs) are essential. Therefore, substantial efforts and progress have been made to attain superior design/engineering and optimization of the inorganic NCs with a focus on surface quality, reduced nonradiative charge carrier recombination centers, and improved colloidal stabilities. Metal-ion doping has been proven to have a robust influence on the electronic band structure, PL behavior, and charge carrier recombination dynamics. Thus, in this perspective, we summarize the recent progress of the significant impact of metal cation doping on the optical properties, including the PL enhancement of CsPbCl3, CsPbBr3, and CsPbI3 perovskite NCs. Moreover, we shed light on the mechanism behind such improved properties. We conclude by recommending possible aspects and strategies to be further explored and considered for better utilization of these doped NCs in thin-film optoelectronic and energy conversion devices.

Tunable Photocatalytic Properties of Planar GaN/GeC Hetero-Bilayer: Production of H₂ Fuel

Novel GaN-based van der Walls (vdW) hetero-bilayer (HBL) is systemically studied through the first-principles density functional theory (DFT) framework to explore its optoelectronic property facilitated photocatalytic activity for hydrogen (H2) fuel production. The vdW concept of planar GaN with GeC monolayer, together making stacked hetero-bilayer, shows unique and tunable optoelectronic properties that fulfill all the photocatalysis attributes. The confirmation of chemical and dynamical stabilities is made with negative interlayer binding energy and non-negative frequency in phonon spectra, respectively. Among the dynamically stable hetero-bilayers, binding energy in HBL 2 (AB1) is the lowest and interlayer distance ~2.954Å is the smallest. The HBLs are sensitive to the stacking arrangements, where HBL 2 demonstrates type-I direct bandgap and HBL 6 (AB6) is Type-II direct bandgap. The intrinsic HBLs show superior carrier mobility as their effective masses are lower from their constituent monolayers. Also, the intrinsic absorption coefficient of the HBLs increase as high as ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , 10 times greater than conventional perovskite materials, which show outperforming optoelectronic conversion efficiency. Additionally, the HBLs are highly tunable in both bandgap and type due to biaxial strains and cross-plane electric fields. With biaxial strains, from compressive to tensile, both HBLs show monotonous bandgap lowering with a dominant direct-indirect bandgap splitting in HBL 2. Interestingly, for all the biaxial strains within the -6% to +6% range, both HBLs have sufficient kinetic overpotential for photocatalytic water splitting and an increase in visible peak by 3.5 (2) times in the HBL 6 (HBL 2). Electric fields also increase the photocatalytic water splitting performance with a net bandgap lowering and increasing the visible absorption peak by ~1.5 times compared with intrinsic HBLs. These promising properties that we have found in the planar GaN/GeC vdW hetero-bilayer are highly suggestive for the impending use of this material in photocatalytic water splitting technology to produce H2 fuel.

Using the next generation combined digital transformers

The paper considers and analyzes the use of new generation combined digital instrument transformers (DIT) with an optoelectronic conversion unit and a combining module or a stand-alone combining module, an external synchronization source or an internal clock generator and digital interfaces.

Synthesis and characterization of triarylamine‐based polyimides for electrochromic and optoelectronic conversion behaviors

ABSTRACTIn this study, four novel triarylamine‐based polyimides with different substituted groups (tert‐butyl and ‐H) containing pyrrole moieties were successfully prepared by polycondensation reaction. The electrochemical and electrochromic properties of the polyimides were measured by cyclic voltammetry and spectro‐electrochemistry. The polyimides exhibited obvious electrochromic behavior with good thermal stability (the 10% weight‐loss temperatures were recorded in the range of 345‐386°C), film‐forming ability and reversible stability after 1000 s. The color of the polyimide films changed from colorless to light blue or yellow to blue on increasing the applied potential. The highest coloration efficiency reached up to 190 cm2C−1. The polyimide films exhibited a stable response to the light (on or off) after 200 s. Especially, PyHBTPI displayed effective solubility, superior optical contrast (~30%) in the visible region, faster response time (1.19 s for coloring process), and obvious color change from yellow to blue with good stability, thus, confirming the potential use for high contrast displays. Overall, the study demonstrates the successful development of high‐performance polyimides for electrochromic and optoelectronic behaviors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48808.

Schottky barrier height of epitaxial lattice-matched TiN/Al0.72Sc0.28N metal/semiconductor superlattice interfaces for thermionic energy conversion

Since the initial development of semiconductor heterostructures in the 1960s, researchers exploring the potential of artificially structured materials for applications in quantum electronic, optoelectronic, and energy conversion devices have sought a combination of metals and semiconductors, which could be integrated at the nanoscale with atomically sharp interfaces. Initial demonstration of such metal/semiconductor heterostructures employed elemental polycrystalline metal and amorphous semiconductors that demonstrated electronic tunneling devices, and more recently, such heterostructures were utilized to demonstrate several exotic optical phenomena. However, these metal/semiconductor multilayers are not amenable to atomic-scale control of interfaces, and defects limit their device efficiencies and hinder the possibilities of superlattice growth. Epitaxial single-crystalline TiN/Al0.72Sc0.28N metal/semiconductor superlattices have been developed recently and are actively researched for thermionic emission-based waste heat to electrical energy conversion, optical hyperbolic metamaterial, and hot-electron solar-to-electrical energy conversion devices. Most of these applications require controlled Schottky barrier heights that determine current flow along the cross-plane directions. In this Letter, the electronic band alignments and Schottky barrier heights in TiN/Al0.72Sc0.28N superlattice interfaces are determined by a combination of spectroscopic and first-principles density functional theory analyses. The experimental EF(TiN)-EVBM(Al0.72Sc0.28N) at the interfaces was measured to be 1.8 ± 0.2 eV, which is a bit smaller than that of the first-principles calculation of 2.5 eV. Based on the valence band offset and the bandgap of cubic-Al0.72Sc0.28N, an n-type Schottky barrier height of 1.7 ± 0.2 eV is measured for the TiN/Al0.72Sc0.28N interfaces. These results are important and useful for designing TiN/Al0.72Sc0.28N metal/semiconductor superlattice based thermionic and other energy conversion devices.