Search

The emergence of optical Internet of Things (optical-IoT) for sixth-generation (6G) networks has been envisaged to relieve the bandwidth congestion in the conventional radio frequency (RF) channel, and to support the ever-increasing number of smart devices. Among the plethora of device innovations deemed essential for fortifying the development, herein we report on the visible-to-near-infrared color-conversion luminescent-dyes based on lead sulphide quantum dots (PbS QDs), so as to achieve an eye-safe high-speed optical link. The solution-processed PbS QDs exhibited strong absorption in the visible range, radiative recombination lifetime of 6.4 μs, as well as high photoluminescence quantum yield of up to 88%. Our proof-of-principle demonstration based on an orthogonal frequency-division multiplexing (OFDM) modulation scheme established an infrared data transmission of 0.27 Mbit/s, readily supporting an indoor optical-IoT system, and shed light on the possibility for PbS-integrated transceivers in supporting remote access control of multiple nodes. We further envisaged that our investigations could find applications in future development of solution-processable PbS-integrated luminescent fibers, concentrators, and waveguides for high-speed optical receivers. [ABSTRACT FROM AUTHOR]

An effective strategy based on optical tunneling is developed to significantly improve the efficiency of quantum dots light-emitting diodes (QLEDs) and perovskite light-emitting diodes (PeLEDs). Contrary to the common impression that the hole transport layers (HTL) with low refractive index will severely confine lights according to Snell's law, optical tunneling unlocks a channel to extract the lights through HTL. In this work, we demonstrate the light beyond the critical angle still has a chance to penetrate into the substrate and finally emit outside the device. An optical tunneling model is also presented here to quantitatively describe the light extraction through optical tunneling and reveal related factors. Applying a thin HTL (thickness = 10 nm) and a high-index substrate (refractive index = 2) in the typical device architecture (Glass/ITO/PEDOT:PSS/EML/TPBi/LiF/Al), substrate modes can be improved from 18% to 60%. Therefore, optical tunneling followed by EES is believed to be a cost-effective strategy to enhance light extraction efficiency. This work unravels the potential to further significantly improve the efficiency of QLEDs and PeLEDs. [ABSTRACT FROM AUTHOR]

Colloidal nanoplatelets (NPLs) are a kind of two-dimensional nano-material with an atomically flat surface, leading to an ultra-narrow emission linewidth of 8~12 nm. In this article, we fabricated green light-emitting diodes (LEDs) based on CdSe/CdS core/crown NPLs. This device exhibited an electroluminescence (EL) at 521 nm with a full-width at half maximum (FWHM) of 15 nm and a maximum luminance of 4684 cd/m2. Such narrow EL FWHM indicates that the core/crown NPLs can achieve an ultrapure green LED with 124.7% of National Televison System Committee (NTSC), realizing a high color saturation and wide color gamut display. [ABSTRACT FROM AUTHOR]

We propose a liquid-crystal-based reconfigurable chiral metasurface absorber and numerically investigate its chiro-optical properties. The chiral metasurface absorber consists of a metal–insulator–metal structure with the substrate, which can strongly absorb a circularly polarized wave of one spin state and reflects that of the opposite spin, resulting a strong circular dichroism (CD). A birefringent liquid crystal (LC) is exploited to serve as the insulator layer in the metal–insulator–metal structure. We could then vary the circular state of the incident light by controlling the alignment of the LC molecules, hence inversing the CD. The simulation results show that the CD will change the sign as the LC molecules are realigned from 0° to 90°. The absorption efficiency for the specific circularly polarized wave is larger than 80% and the CD is nearly 70%. The simple and compact design of our proposed chiral metasurface absorber is especially favorable for integration, and such a reconfigurable chiral absorber could find many potential applications in biological detection/sensing, polarimetric imaging, and optical communications. [ABSTRACT FROM AUTHOR]

We report for the first time the synthesis of quasi-two-dimensional (2D) perovskite nanoplates by incorporating 2D TMA2PbBr4(C4H9NH3, TMA) into formamidinium (FA) based 3D perovskite nanocrystals via the facile solution-processed method. In this way, we achieve morphology evolved quasi-2D perovskite TMA2(FA)n− 1PbnBr3n+ 1. The steady-state photoluminescence is blueshifted as the perovskite is dimensionally tuned from 3D to 2D, which is normally attributed to the structure relaxation. The optical properties of quasi-2D perovskite nanoplates can also be achieved by tuning the acidity of the reaction precursor. The proposed configuration and growth mechanism of quasi-2D TMA2(FA)n− 1PbnBr3n+ 1perovskite with differentnvalues has been further confirmed by Raman spectroscopy. This study opens up opportunities for fundamental research on the synthesis and characterization of quasi-2D perovskite nanoplates and introduces a new family of quasi-2D solution-processed perovskites for optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this letter, a compact 60-GHz on-chip bandpass filter is presented using an integrated passive devices technology on a GaAs substrate. An E-shaped dual-mode resonator and stepped impedance resonator were adopted in this design for a compact size and sharp cut-off response. Two controllable transmission zeros are obtained on the both sides of the passband achieving a good frequency selectivity. The main size of the filter is only $0.58 \times 0.4$ mm2. The presented filter has a center frequency of 60 GHz, with a 3 dB fractional bandwidth of 14.8 GHz from 52.6 to 67.4 GHz. The insertion loss of the filter is only 1.2 dB, and the return loss is lower than −10 dB within the passband. Good agreement is achieved between the measured results and the simulated ones. [ABSTRACT FROM AUTHOR]

In this paper, the ambient doping effect on negative/positive bias temperature instability (NBTI/PBTI) of single layer graphene field effect transistors (FETs) is investigated. In ambient air, the \Delta Vth of NBTI is comparable with that of PBTI under the same stress voltage at room temperature. The \Delta Vth of NBTI appears insensitive to temperature, while the \Delta Vth of PBTI increases significantly with rising temperatures, due to the thermally activated charging of ambient doped defects at the graphene/SiO2 interface. This effect also results in an abnormal recovery of NBTI. In an ambient vacuum, the \Delta Vth is much less than that in ambient air. In addition, the \Delta Vth of both NBTI and PBTI decreases substantially for higher temperatures in the vacuum. The adsorbed molecules are mainly responsible for the \Delta Vth under BTI stress and the back-gated graphene FETs in the air. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) make an important class of optoelectronic devices, increasingly used in lighting and displays. Conventional InGaN/GaN LEDs of c-orientation exhibit strong internal polarization fields and suffer from significantly reduced radiative recombination rates. A reduced polarization within the device can improve the optical matrix element, thereby enhancing the optical output power and efficiency. Here, we have demonstrated computationally that the step-doping in the quantum barriers is effective in reducing the polarization-induced fields and lowering the energy barrier for hole transport. Also, we have proven experimentally that such InGaN/GaN LEDs with Si step-doped quantum barriers indeed outperform LEDs with wholly Si-doped barriers and those without doped barriers in terms of output power and external quantum efficiency. The consistency of our numerical simulation and experimental results indicate the effects of Si step-doping in suppressing quantum-confined stark effect and enhancing the hole injection, and is promising in improving the InGaN/GaN LED performance. [ABSTRACT FROM PUBLISHER]

This paper proposes some novel substrate-integrated waveguide (SIW) bandpass filters combined with planar resonators. According to specific topologies, microstrip lines with different electrical lengths are introduced into their designs. Their corresponding phase-shift characteristics are used to obtain the desired couplings between SIW cavities and the microstrip resonator. Two third-order filter samples are realized. One has a single transmission zero below the passband and the other possesses a quasi-elliptic response. Further, a fourth-order filter is developed by effectively superpositing two individual third-order topologies. It shows better frequency selectivity and flat in-band group delay, with good agreement between the measured and the simulated S-parameters. Their compactness and high rejection in the stopbands make them very suitable for system-on-package. [ABSTRACT FROM AUTHOR]

Large-scale rationally designed periodic Si nanopillar (SiNP) arrays of varying diameters and heights have been fabricated by a top-down method. The impacts of the structural parameters (e.g., diameter/periodicity/height) on the reflectance and absorption of the SiNP array have been extensively studied, and the results are in agreement with our theoretical prediction of Li Owing to the notably enhanced light absorption of the optimized SiNP array, a short-circuit current density Jsc of 34.3 \mA/cm^2 was obtained on an axial p-n SiNP array surface-textured solar cell, which is the highest to date among reported Si nanowire/SiNP-based solar cells. Jsc is significantly boosted compared to that of the untextured solar cell (18.1 \mA/cm^2), which implies that the SiNP array is a promising texturing technology for thin-film photovoltaic application. [ABSTRACT FROM PUBLISHER]

A Sn-doped \Ga2\O3 thin film was deposited on a \n^+-Si substrate by metal–organic chemical vapor deposition. The \Ga2\O3 film was found to be amorphous-like and exhibited n-type conduction with Sn doping. Room-temperature electroluminescence was clearly observed from the \Sn:Ga2\O3/\n^{+}-Si diode, including an ultraviolet (UV) emission at \sim370 nm, a yellow emission at \sim580 nm, and a red emission at \sim680 nm. The UV emission is assigned to the transition from \SnGa donor to the VGa acceptor, whereas the visible emissions were assigned to be related to the dangling bond defects. [ABSTRACT FROM PUBLISHER]

Inkjet-printed In-Ga-Zn oxide (IGZO) thin-film transistors (TFTs) with bottom-gate bottom-contact device architecture are studied in this paper. The impact of the IGZO film thickness on the performance of TFTs is investigated. The threshold voltage, field-effect mobility, on and off drain current, and subthreshold swing are strongly affected by the thickness of the IGZO film. With the increase in film thickness, the threshold voltage shifted from positive to negative, which is related to the depletion layer formed by the oxygen absorbed on the surface. The field-effect mobility is affected by the film surface roughness, which is thickness dependent. Our results show that there is an optimum IGZO thickness, which ensures the best TFT electrical performance. The best result is from a 55-nm-thick IGZO TFT, which showed a field-effect mobility in the saturation region of 1.41 \cm^2/\V\cdot\s, a threshold voltage of 1 V, a drain current on/off ratio of approximately \4.3 \times \10^7, a subthreshold swing of 384 mV/dec, and an off-current level lower than 1 pA. [ABSTRACT FROM AUTHOR]

We shall present a cosensitized solar cell with sequentially assembled CdS quantum dots (QDs) and black dye on a flower-like ZnO rod nanostructure. As revealed by UV-vis absorption spectrum and scanning electron microscopy CdS QDs and black dye can be effectively adsorbed onto a flower-like ZnO nanorod array. Besides acting as a sensitizer, CdS QDs layer helps to prevent formation of Zn^2+/dye complex. CdS QDs also provide intermediate energy levels for excited electron transfer from black dye to ZnO film. A power conversion efficiency as high as 3.26% was achieved for CdS QD and black dye cosensitized ZnO photoanode under the illumination of one Sun (AM1.5G, 100 mW/cm^2). [ABSTRACT FROM PUBLISHER]

An 85 to 110 GHz high efficiency, high output power frequency doubler is presented in this letter. The traveling-wave topology is used to generate even harmonics and suppress odd harmonics effectively. The output fundamental and 4th harmonic reflectors are applied to enhance the efficiency, conversion gain and fundamental rejection. The measured results show a peak conversion gain of 3.2 dB and peak efficiency of 11.2% with a saturated output power of 9 dBm at 100 GHz. The doubler exhibits higher than 30 dB fundamental rejection from 85 to 110 GHz with a compact chip size of 1.5\,\times\,0.9 mm^2. [ABSTRACT FROM PUBLISHER]

In this letter, we report a solution-processed hafnium indium zinc oxide (HIZO) thin-film transistors (TFTs) with an Al-doped ZrO2 (AZO) gate dielectric. The AZO thin films were identified as an amorphous phase up to the annealing temperature of 600 ^\circC and had a smooth surface with root-mean-square roughness of <0.35~nm . The relative dielectric constant of AZO thin film annealed at 400 ^\circC is 19.67. And HIZO TFTs with AZO gate oxide exhibited a high saturation field-effect mobility of 18.1 cm^2 /Vs, a small subthreshold swing of 0.4 V/decade, and a high ON/OFF ratio of 10^7 , which can satisfy the backplate requirements for flat panel displays. [ABSTRACT FROM AUTHOR]

A novel broadband compact lumped-element balun with a tail inductor is proposed in this letter. The employment of tail inductor improves amplitude and phase balances for better broadband performance. Furthermore, compared with baluns utilizing conventional micro-strip approaches or second-order lattice topology, this proposed topology offers significant circuit size reduction. Theoretical analysis of the optimized tail inductor value is presented to improve operation bandwidth. The concept is realized and validated by a 2.45 GHz balun with surface mounted devices (SMD). The measured results illustrate an amplitude balance less than 0.5 dB and a phase balance less than \pm 6^\circ in a 36.7% bandwidth. The insertion loss is around 3.6 dB while the return loss of the unbalance port is better than 15 dB in the whole working frequency range. The core circuit occupies only 2 mm \times 2.5 mm limited by SMD size. [ABSTRACT FROM PUBLISHER]

A set of miniaturized dual-band bandpass filters is presented with a quadruple-folded substrate integrated waveguide (SIW) implemented into each design. They were fabricated using standard low temperature co-fired ceramic (LTCC) technology. The bandwidths of both passbands of the filters are adjustable independently by changing the geometrical parameters of the coupling structure. Two filter samples are demonstrated with central frequencies located at 2.4/5.2 and 2.4/5.7 GHz, respectively, and their measured S-parameters agree well with the simulated ones. [ABSTRACT FROM PUBLISHER]

A compact substrate integrated waveguide (SIW) filter with defected ground structure (DGS) is proposed. The DGS is etched on the ground plane of the SIW cavity, and it behaves as a resonator. Under such condition, better frequency selectivity contributed to three transmission zeros is obtained, and two of them are located at the lower stopband. The proposed filter, fabricated using standard printed circuit board technology, has the advantages of compactness, good spurious suppression characteristics and low cost. Its measured S-parameters agree well with the simulated ones. [ABSTRACT FROM PUBLISHER]