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Using the transfer matrix method, the absorption, reflection, and nonreciprocity of the cylindrical photonic crystals (CPCs) consisting of graphene and two layers of ordinary medium cascaded by a periodic sequence and a Rudin–Shapiro quasiperiodic sequence are investigated under a large incidence angle of electromagnetic wave. By comparing the cascade of two periodic structures and the case of a single periodic structure, it is concluded that the structure proposed in this paper has better nonreciprocal phenomena and wider relative absorption bandwidth at a large incidence angle, reaching 162.2%, which is also much higher than the general planar photonic crystals. The absorption performance of this structure in TE and TM modes is compared at different angles and it is found that TM mode has a wider absorption bandwidth and has an ideal bandwidth in a large range of incident angle from 20° to 80°. Meanwhile, the optimum parameters of chemical potential and medium thickness are discussed, which can meet the requirements of large absorption bandwidth and significant nonreciprocity at a large incident angle. The CPCs embedded in graphene adopted in this paper are structures that have never been studied before. The electrical conductivity of graphene can be adjusted by the chemical potential, which can more conveniently realize many optical phenomena and provide reference and application values for optical sensing, optical filtering, and optical detection.

Most of the photonic valley-Hall edge states were constructed by changing structures to break the spatial inversion symmetry, restricting the practical application potential. In this paper, we construct a tunable topological valley-Hall edge state based on the large optical Kerr effect. It is demonstrated that topological phase transition happens by engineering the intensity of the injected pump and that a valley-Hall edge state can be generated at the interface between two regions with different topological properties. In addition, eigenfrequency and transmission characteristics of the edge state as a function of applied pump intensity are investigated. The topological protected valley-dependent transmission is studied under non-uniform distributed pump intensity. This work may open a new path toward designing reconfigurable all-optical metadevices.

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility ( μe), electron transport time ( TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

Electric and magnetic modes establish the basis of the localized spoof surface plasmons (LSSPs), both of which are transverse electric (TE) modes. In this paper, the concept of transverse magnetic (TM) modes of LSSPs is proposed, and the double-layer planar-circular-grating resonator is demonstrated to support the TM modes in addition to the TE modes. In numerical simulations, the TE and TM modes were excited by a plane wave and an aperture, respectively, and their resonant frequencies and electromagnetic field distributions were demonstrated to be different. The electric field of the TE mode is parallel to the grating, while the magnetic field of the TM mode is parallel to the grating. In experiments, multiple TE and TM LSSPs modes were excited by a magnetic coupler. The magnetic coupler can be rotated to distinguish the TM modes from the TE ones, which provides conclusive evidence of the existence of the TM modes. Compared with the TE LSSPs modes, the TM LSSPs modes have the advantages of high sensitivity to the distance between layers and high quality factors (Q-factors), which hold promise for providing improvements on compact applications of LSSPs. Based on the proposed concept, therefore, the classification standard of the LSSPs is expanded to make it more scientific and comprehensive.

This paper presents systematic modeling and performance analyses of a 340-GHz dual-polarized antenna-coupled single-sideband (SSB) high-Tc superconducting (HTS) mixer for terahertz (THz) communication systems. The mixer features a fully monolithic-integrated circuit layout, which enables both sensitive heterodyne detection and high image rejection by appropriate polarization-manipulating operation. To predict the comprehensive performance of such a HTS mixer with relatively complicated network architecture and polarization relationships, an innovative modified three-port modeling approach is presented and developed by theoretical derivations. Using the measured Josephson junction parameters of our previous experimentally demonstrated HTS mixer module at the same band, the best conversion gain and SSB noise temperature of the presented mixer are predicted to be around −5 dB and 1200 K at the operating temperature of 40 K, respectively. In addition, the mixer exhibits a flat frequency response over a wide intermediate-frequency range from 15 to 25 GHz and high image rejection of more than 17 dB over the radio frequency operation range. The SSB HTS Josephson mixer will be useful for THz wireless communication applications.

Semi-transparent photovoltaic devices for building integrated applications have the potential to provide simultaneous power generation and natural light penetration. CuIn$_{1-x}$Ga$_x$Se$_2$ (CIGS) has been established as a mature technology for thin-film photovoltaics, however, its potential for Semi-Transparent Photovoltaics (STPV) is yet to be explored. In this paper, we present its carrier transport physics explaining the trend seen in recently published experiments. STPV requires deposition of films of only a few hundred nanometers to make them transparent and manifests several unique properties compared to a conventional thin-film solar cell. Our analysis shows that the short-circuit current, Jsc is dominated by carriers generated in the depletion region, making it nearly independent of bulk and back-surface recombination. The bulk recombination, which limits the open-circuit voltage Voc, appears to be higher than usual attributable to numerous grain boundaries. When the absorber layer is reduced below 500 nm, grain size reduces resulting in more grain boundaries and higher resistance. This produces an inverse relationship between series resistance and absorber thickness. We also present a thickness-dependent model of shunt resistance showing its impact in these ultra-thin devices. For various scenarios of bulk and interface recombinations, shunt and series resistances, AVT and composition of CuIn$_{1-x}$Ga$_x$Se$_2$, we project the efficiency limit which - for most practical cases - is found to be $\leq$10% for AVT $\geq$25%.

Structure-engineered silicon exhibits a wealth of unique optical properties below its bandgap, which holds promise for mid-infrared and terahertz applications such as photodetection, thermophotovoltaics, radiative cooling, and spectroscopy. In this paper, we investigate enhancement mechanisms of sub-bandgap absorption of black silicon fabricated into periodic pyramids. Our measurements indicate that the pyramid structure leads to an enhanced broadband absorption in the wavelength region from 1.5 to 13.07 μm with an efficiency of over 80%. The broadband absorption enhancement is shown to originate from the Rayleigh–Wood anomaly, localized magnetic plasmonic resonance, and graded-index effect, which together facilitate the interaction between light and free-carriers in silicon. These results are helpful for understanding the interaction between light and black silicon.

GaN technology is not only gaining traction in power and RF electronics but is also rapidly expanding into other application areas including digital and quantum computing electronics. This paper provides a glimpse of future GaN device technologies and advanced modeling approaches that can push the boundaries of these applications in terms of performance and reliability. While GaN power devices have recently been commercialized in the 15–900 V classes, new GaN devices are greatly desirable to explore both higher-voltage and ultra-low-voltage power applications. Moving into the RF domain, ultra-high frequency GaN devices are being used to implement digitized power amplifier circuits, and further advances using the hardware–software co-design approach can be expected. On the horizon is the GaN CMOS technology, a key missing piece to realize the full-GaN platform with integrated digital, power, and RF electronics technologies. Although currently a challenge, high-performance p-type GaN technology will be crucial to realize high-performance GaN CMOS circuits. Due to its excellent transport characteristics and ability to generate free carriers via polarization doping, GaN is expected to be an important technology for ultra-low temperature and quantum computing electronics. Finally, given the increasing cost of hardware prototyping of new devices and circuits, the use of high-fidelity device models and data-driven modeling approaches for technology-circuit co-design are projected to be the trends of the future. In this regard, physically inspired, mathematically robust, less computationally taxing, and predictive modeling approaches are indispensable. With all these and future efforts, we envision GaN to become the next Si for electronics.

Naturally occurring materials with hyperbolic optical properties are attracting considerable interest due to their ability to confine light in small volumes and their resulting potential for applications in photonics. This paper uses a first-principles theoretical approach without adjustable parameters to investigate the hyperbolic optical properties of bulk calcite (CaCO3). This material exhibits natural hyperbolic behavior within its Reststrahlen bands at 1403–1552 and 864–887 cm−1. The calculated results are shown to be in good agreement with our reflectance data obtained from frequency- and polarization-dependent measurements. These results show that calcite is an attractive natural hyperbolic material; in addition, it has the advantage of low losses and is available commercially in a variety of crystal orientations.

Two-dimensional black phosphorene (BP) has attracted much interest for application in electronic devices. Contacts between BP and metal electrodes are critical components of BP-based devices and can dramatically affect device performances. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, and potential distribution for interface systems of Al-, Au-, Cu-, Ni-, and Ti-monolayer BP in surface contact and edge contact (EC) types. Moreover, we also used density functional theoretical coupled with the nonequilibrium Green’s function method to investigate contact resistances and Schottky barrier heights (SBHs) for transport systems of monolayer BP with Al, Au, Cu, Ni, and Ti electrodes. Our calculated results indicate that the contact type between BP and metals may greatly affect electrical properties of BP–metal contacts. Changing contact type between metal electrodes and BP channel can change the type of Schottky barrier of metal–BP contacts. The contact barrier of metal–BP depends on the metal material. Selecting an appropriate contact type and metal can effectively regulate the contact barrier of metal–BP. Specifically exciting, our estimated lateral SBHs for the Ni–BP system in EC-type agree well with the experimental results. We have provided a new strategy on choosing an appropriate contact type to achieve low contact resistance for the metal–BP interface.

In SiN/AlGaN/GaN heterostructures, the evaluation of interface charges at the SiN/AlGaN and AlGaN/GaN interfaces is crucial since they both rule the formation of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. In this paper, we conducted a thorough analysis of the gate-to-channel capacitance CGC(VG) and of the drain current ID(VG) over a gate voltage VG range enabling the depletion of the 2DEG and the formation of the electron channel at the SiN/AlGaN interface. This work includes the establishment of analytical equations for VTH1 (formation of the 2DEG) and VTH2 (formation of the electron channel at the SiN/AlGaN interface) as a function of interface charges and of the p-doping below the 2DEG. The inclusion of the p-doped layer below the 2DEG and the use we made of VTH2 have not been reported in previous studies. Our analysis allows a reliable estimate of the interface charges at the AlxGa1−xN/GaN and SiN/AlxGa1−xN interfaces for various Al concentrations x as well as to demonstrate that the polarization charge at the SiN/AlxGa1−xN interface is compensated, which confirms previous findings. Moreover, this compensation is found to be induced by the AlGaN layer rather than the SiN layer.

In this paper, we investigate the formation of a photonic terajet and tune its optical properties using the high-resolution finite-difference time-domain method. A Dirac semimetal is coated onto the surface of a dielectric rod and illuminated with an incident plane wave. The refractive index of the Dirac semimetal can be modulated by changing its Fermi energy. It was demonstrated that the presence of the Dirac semimetal layer can significantly affect the characteristics of the photonic terajet, such as focal distance, intensity, full-width at half maximum, and length.

Since their initial demonstration in 1995, light-emitting electrochemical cells (LECs) have received attention due to potential advantages over traditional polymer optoelectronic devices. A standard LEC consists of two electrodes surrounding an active layer that contains polymer and mobile ions. When a bias is applied, the ions separate and move toward the electrodes, creating a reversible p–n junction analog. Immobilizing the ions after ion dissociation using one of several demonstrated methods to create a “fixed-junction LEC” allows the device to produce a significant photovoltaic response. Recently, our group demonstrated chemically fixed junction LECs using a polymerizable ionic liquid (ATOA-AS) that conferred important advantages over first-generation chemically fixed junction devices, including improved phase compatibility and turn-on time. Early tests showed improvements in the performance of these devices over the first chemically fixed junctions in terms of light-emitting properties. However, their photovoltaic behavior has not been previously investigated. In this paper, we demonstrate photovoltaic behavior in chemically fixed junction LECs based on the polymerizable ionic liquid ATOA-AS as the ion source. While further improvements in the photovoltaic performance of fixed-junction devices still need to be made before they are considered a commercially viable technology, we find that the devices reported here compare well to other single-layer polymer homojunction solar cells and demonstrate an exceptionally high VOC (>1.8 V for some configurations). We also explore the effects that changes to various aspects of device composition and testing procedures have on device performance.

Table-top neutron/x-ray sources are of great interest for uses in neutron activation analyses, in neutron/x-ray radiography, and also in medical applications. Inertial electrostatic confinement fusion (IECF) is a multiple neutron source that can emit neutrons, protons, x rays, etc., as basic products when operated in both continuous and pulsed modes. In this work, D-D neutrons are produced in the steady-state mode using a cylindrical IECF device. The neutron production rate has been optimized by using cathodes having different dimensions and geometrical transparencies. The maximum neutron production rate is found to be approaching 107n/s, using a cathode having eight grid wires and a diameter of 3 cm. The neutrons are successfully used for neutron activation analysis of materials containing explosive elements. X-ray spectrum having a wide range of photon energies (30–70 keV) has been detected from this device while operated in the continuous mode. X-ray radiography of high density objects has also been performed and reported for the first time using the cylindrical IECF source with negative polarity of the central grid in this paper.

Applying atmospheric plasma etching to the surface texturing process of silicon solar cells is a promising strategy for the current photovoltaic manufacturing industry due to its low equipment cost and good fabrication flexibility. This paper investigates the morphology evolution of the silicon surface etched by an Ar/CF4/O2 plasma and the associated optical properties. Results show that the generation of the light trapping structure on the polished silicon surface can be divided into two stages on the basis of the multi-scale morphological images and the quantitative evaluation of roughness parameters. The initial roughening stage mainly involves the formation of high-frequency nanoroughness that can act as an effective medium layer with a gradual refractive index. The resulting optical medium effect can reduce the surface reflectance within a broad range of wavelengths. At the next texturing stage, the low-frequency and high-amplitude microroughness dominates the morphology of the etched silicon surface. It features inverted parabolic structures with a high aspect ratio, which can cause multiple reflections of the incident light. The optical medium effect resulting from the nanoroughness is also inherited. Thus, the anti-reflectance property of the etched silicon surface is greatly improved. This work demonstrates that the light trapping properties of silicon surface etched by atmospheric plasma jet are a synergy of the optical medium effect and geometrical optics. Insights into the morphology evolution and optical properties of the textured surfaces are important for developing a new surface texturing process of silicon solar cells.

Ultra-wide bandgap semiconductors with exceptional advantages have potential use in ultrahigh power, ultrahigh frequency devices, and other applications. In this paper, a series of high-quality Nb-doped ZrxSn1−xO2 (Nb:ZrxSn1−xO2) alloy epitaxial films were prepared on c-plane sapphire substrates by pulsed laser deposition. A greater proportion of Zr successfully widened the optical bandgap of SnO2 up to 4.70 from 4.28 eV. Interestingly, although Nb is a common n-type dopant for SnO2, the conductivity of Nb:ZrxSn1−xO2 decreased with increasing Zr content. The greater activation energy Ea of the films with more Zr contents was determined by variable resistance measurements and rationalized by the first-principles calculations. The higher Zr content leads to a lower conductivity in the films. This is because the electronegativity of Zr is smaller than that of Sn and Nb, making it easier for O to attract electrons from Zr and Nb donating less electrons with increasing Zr content. It leads to more electrons filling the Nb 4d orbital and brings the donor level further down from the conduction band minimum. However, Nb:ZrxSn1−xO2 with a low Zr content of x = 0.1 has good electrical conductivity, with a carrier density of 5.426 × 1020 cm−3 and a resistivity of 7.89 × 10−3 Ω cm, and simultaneously a broadened bandgap of 4.4 eV. Therefore, Nb can act as an effective n-type dopant for ZrxSn1−xO2 with proper Zr content, making Nb-doped ZrxSn1−xO2 promising for developing ultraviolet-transparent conductive electrodes.

Gaseous detectors are widely used in high energy physics, and are attractive choices in tracking systems for cosmic muon imaging, also called muography. Such detectors offer high resolution and high efficiency at reasonable cost for large sizes, however, one of the drawbacks is that the gaseous detection medium must be prevented from contamination by outside air or internal outgassing. Standard systems work with a constant gas flow, leading to regular maintenance in the form of gas cylinder changes, which can be an issue for remote field applications. In this paper we discuss the practical possibilities to reduce gas consumption of an outdoor gaseous tracker, where particularly the gas density change from daily temperature cycling limits the input flow. Such "breathing" effect can be circumvented by well designed buffer volume, which must prevent external air contamination. A realistic MWPC tracking test system with 0.9 square meter area, total volume of 160 l, has been operated for 36 days with a flow of 3 l/day, confirming that the buffer volume, in this case a 50 m long and 10 l volume low diffusion tube, ensures sufficient gas quality. The key effects governing the gas flow dynamics, including diffusion and gas volume change, has been studied quantitatively, leading to practical design prescriptions., Comment: 20 pages, 12 figures. The following article has been submitted to Journal of Applied Physics under Manuscript #JAP21-AR-01969

Investigation of the polarization switching mechanism in ferroelectric hafnium zirconium oxide (HZO) film is of great importance for developing high-quality ferroelectric memory devices. Recently, several works have been reported to describe the switching process of polycrystalline HZO film using the inhomogeneous field mechanism (IFM) model. However, no report has recorded the effect of high pressure annealing (HPA) on the polarization switching process. In this paper, we have carried out a careful investigation on the switching properties of HZO capacitors annealed at 600 °C with various high pressure conditions (1, 50, and 200 atm) using the IFM model. As pressure increases to 200 atm, the ferroelectric properties were enhanced in the HZO films, and, as a result, highest remanent polarization (Pr of 24.5 μC/cm2) was observed when compared with 1 and 50 atm. Similarly, as HPA increases, the HZO capacitors showed a decrement of the coercive field, which significantly improved the switching properties. The time consumed for reversing 80% polarization was 113.1, 105.7, and 66.5 ns for the sample annealed at 1, 50, and 200 atm, respectively. From the IFM model, the smallest active field (2.997 MV/cm) and a uniform distribution of the local electric field (0.304) were observed at 200 atm. Furthermore, the characteristic time constant ( τ 0 ) showed a decreasing trend (34.7, 18.1, and 11.7 ps) with increasing HPA. The improved switching properties and detailed findings recorded in this study may be helpful for developing the ferroelectric hafnia based non-volatile memory applications.

Dynamic control of probe absorption spectrum via vortex beams in multilevel systems has attracted much attention because it provides an avenue to observe unique transport properties. In this paper, we employ experimentally accessible parameters to flexibly control the probe absorption spectrum that shows vortex-induced transparency (VIT) and absorption (VIA) phenomena. Specifically, this system can be served as an optical switch while the vortex beams can act as the control knob, which has the ability to switch from a transparency dip to an absorption peak. Differing from a conventional electromagnetically induced transparency technique, our proposed scheme investigates VIT and VIA by tuning the orbital angular momentum of vortex beams in the resonance and non-resonance cases. Moreover, the collective feature caused by constructive or destructive interference is also studied via adjustable frequency detuning. Our results may provide an efficient approach to study similar phenomena in multilevel quantum systems driven by optical vortex beams.

In this paper, a refractive index (RI) sensor with superconducting photonic crystal in the terahertz regime is theoretically analyzed by the transfer matrix method. An asymmetric resonance cavity containing gradient thicknesses of the superconducting layer is employed to suppress the resonance absorption linewidth. We present the coupled wave theoretical model to give an optimization scheme for excellent sensing performance. The proposed sensing models can achieve an excellent single resonant peak when the temperature is over 80 K. When the incident angle varies between 50° and 70° in TE mode, the shift of a single resonant peak has a linear relationship with the incident angle. The simulation results report that the sensitivity and figure of merit in the optimal model can reach over 22.2 μm RIU−1 (RIU represents RI unit) and 265 at the ultralow temperature (85 K), respectively. Its performance indicators are dozens of times those of the traditional photonic crystal RI sensor. Our study provides theoretical guidance for the design of a low-temperature RI sensor with a high-performance indicator.

This paper addresses the application of multimodal nonlinear optical (MNLO) microscopy to clinical research within the context of label-free non-invasive molecular imaging. Here, a compact MNLO microscope based on a laser scanning microscope, a femtosecond laser, a time-correlated single-photon counting system, and a photonic crystal fiber are introduced for biomedical applications. By integrating two-photon fluorescence, two-photon fluorescence lifetime imaging, second-harmonic generation, and coherent anti-Stokes Raman scattering microscopy, the proposed scheme provides profound insights into the physicochemical properties related to 3D molecular orientation distribution, inter- and intra-molecular interactions, and disease progression in biological systems and organs. The high peak power and the low average intensity of near-infrared laser pulses allow for deep-penetration imaging without compromising sample vitality. Linking nonlinear optical phenomena with time/spectral/polarization-resolved imaging also makes it possible to obtain multidimensional information to address complex biomedical questions.

The use of stibnite (Sb2S3) as a light-harvesting material in thin film solar cells has received considerable research interest during the transition of the millennium. However, the use of perovskite diminished the research in the field, and the potential of antimony Chalcogenides [Sb2(S,Se)3] was not explored thoroughly. Although these materials also provide bandgap tuning like perovskite, by varying the composition of S and Se, it is not as popular as perovskite for the fabrication of solar cells mainly because of the low efficiency of the solar cells based on it. In this paper, we present a landscape of the functional role of various device parameters on the performance of Sb2(S,Se)3-based solar cells. For this purpose, we first calibrate the optoelectronic model used for simulation with the experimental results from the literature. The model is then subjected to parametric variations to explore the performance metrics for this class of solar cells. Our results show that despite the belief that the open circuit voltage is independent of contact layers’ doping in proper band-aligned carrier selective thin film solar cells, here we observe otherwise and the open circuit voltage is indeed dependent on the doping density of the contact layers. Using the detailed numerical simulation and analytical model, we further identify the performance optimization route for Sb2(S,Se)3-based thin film solar cells.

As the grating-based phase contrast imaging has drawn much attention in various scientific fields, there is an increasing demand for a compact imaging system with high efficiency in practical applications. In this paper, a compact imaging configuration by replacing the source grating in a conventional imaging system with a robust, easily-fabricated, and cost-effective x-ray polycapillary lens is proposed and its feasibility is examined using a full-scale Monte Carlo simulation. A typical x-ray spectrum for diagnostic mammography is adopted in the simulation. Under this spectrum, a new polycapillary lens is designed and optimized to meet the requirement of the imaging system. The phantom consists of polyethylene, cortical bone, and adipose tissue spheres of different sizes. An accurate phase image of the phantom is successfully reconstructed using an eight-step phase-stepping method. Excellent agreement of the phase shift and attenuation of the phantom is obtained between the simulation and the theoretical prediction. Compared with a conventional imaging system using a source grating at the same parameters, the imaging efficiency of our proposed system is improved 1.7 times, while its background visibility is reduced from 44.4 % to 12.4 %. Our results suggest the possibility of developing such a bench-top system for flexible phase contrast imaging applications.

A model for ultracapacitor capacitance and ion screening length based on semiconductor physics is presented in this paper. Screening length is related to capacitance as the plate-plate separation in a double-layer, and thus both are related to dissolved ion density in the electrolyte. Furthermore, this dissolved ion density can be expressed in terms of an effective bandgap assigned to the electrolyte/solvent pair. Therefore, by knowing the effective bandgap, we can explain the published experimental measurements of the dependence of capacitance and screening length on temperature. For electrolytes commonly used in ultracapacitor applications, the effective bandgap is estimated to be on the order of a few 100 meV.