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Funding Information: This project was primarily supported by the National Key R&D Program of China (Grant 2018YFA0307200), the National Natural Science Foundation of China (Grants 91950119, 61905196, and 62090033), Key Research and Development Program in Shaanxi Province of China (Grant 2020JZ-10), and the Fundamental Research Funds for the Central Universities (Grants 310201911cx032, 3102019JC008, and D5000210905). The authors also thank the Analytical & Testing Center of NPU for their assistance in device fabrication and characterizations. Publisher Copyright: © 2022 American Chemical Society. Two-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe2p-i-n homojunction fabricated directly on a silicon photonic crystal (PC) waveguide, which enables on-chip photodetection with ultralow dark current, high responsivity, and fast response speed. The adopted silicon PC waveguide is electrically split into two individual back gates to selectively dope the top regions of the MoTe2 channel in p- or n-types. High-quality reconfigurable MoTe2 (p-i-n, n-i-p, n-i-n, p-i-p) homojunctions are realized successfully, presenting rectification behaviors with ideality factors approaching 1.0 and ultralow dark currents less than 90 pA. Waveguide-assisted MoTe2 absorption promises a sensitive photodetection in the telecommunication O-band from 1260 to 1340 nm, though it is close to MoTe2's absorption band-edge. A competitive photoresponsivity of 0.4 A/W is realized with a light on/off current ratio exceeding 104 and a record-high normalized photocurrent-to-dark-current ratio of 106 mW-1. The ultrasmall capacitance of p-i-n homojunction and high carrier mobility of MoTe2 promise a high dynamic response bandwidth close to 34.0 GHz. The proposed device geometry has the advantages of employing a silicon PC waveguide as the back gates to build a 2D material p-i-n homojunction directly and simultaneously to enhance light-2D material interaction. It provides a potential pathway to develop 2D material-based photodetectors, laser diodes, and electro-optic modulators on silicon photonic chips.

Two-dimensional (2D) materials, featuring distinctive electronic and optical properties and dangling-bond-free surfaces, are promising for developing high-performance on-chip photodetectors in photonic integrated circuits. However, most of the previously reported devices operating in the photoconductive mode suffer from a high dark current or a low responsivity. Here, we demonstrate a MoTe

A compact electrical source capable of generating surface plasmon polaritons would represent a crucial step for on-chip plasmonic circuitry. The device fabrication of plasmonic actuator based on Au/SiO2/n++Si tunnel junction and performance have been reported in [ACS photonics, 2021, 8, 7, 1951–1960]. This work focuses on the underlying mechanisms of electroluminescence. The n-type Si samples were doped with concentrations ranging from 1.6 × 1015 cm−3 to 1.0 × 1020 cm−3. A low voltage of 1.4 V for intense light emission was achieved at the highest concentration. The electrical/spectral characteristics and energy band diagrams calculation show two distinct behaviors indicating two distinct mechanisms of light emission are at work in the heavily doped versus the lightly doped Si. In the heavily doped case, the light output is correlated to tunneling current and the subsequent conversion of surface plasmons to photons, while that for the lightly doped case is due to indirect band-to-band recombination in silicon. The results are validated by numerical simulation which indicates that the heavy doping of the n++-Si is necessary to achieve surface plasmon generation via electron tunneling due to the presence of band tail states and their effect on lowering the barrier height.

Light emission from metal-insulator-semiconductor junctions (MISJs) has been explored for decades as a possible on-chip light source; however it is not clear whether the mechanism of light emission is plasmonic in nature or is dominated by electroluminescence. Previous studies only investigated silicon with low doping levels, but here we show that only highly doped silicon allows us to excite surface plasmon polaritons (SPPs) in MISJs via inelastic tunneling. This paper describes the mechanism of charge transport and light emission from silicon-based Au-SiO2-nSi MISJs as a function of the doping level Nd varying from 1.6 × 1015 cm-3 to 1.0 × 1020 cm-3. At low doping levels (Nd ∼1015 cm-3), the MISJs behave as Schottky diodes, and the mechanism of light emission involves a radiative recombination of electrons and holes from minority carrier injection under high applied bias (>5.5 V). With increasing doping levels, the current-voltage characteristics of the MISJs change, resulting in symmetrical current-voltage curves with parabolic conductance behavior characteristic of quantum mechanical tunneling. MISJs with the highest doping level (Nd ∼1020 cm-3) are dominated by quantum mechanical tunneling, and light emission originates from radiative decay of surface plasmon polaritons (SPPs) via scattering at threshold voltages as low as 1.5 V. Our simulations indicate that tunneling over the thin SiO2 barrier between the Au and highly doped nSi excites a hybrid-SPP mode localized to the Au whose dispersion depends on the effective index induced by the SiO2-nSi interface. Our studies show that Si needs to be sufficiently doped to be conductive enough to enable SPP excitation via inelastic tunneling.

A CMOS-compatible plasmonic waveguide with a metal or metal-like strip sandwiched in-between dielectrics has been proposed for intra-chip communication in the more-than-Moore era. A sequence of numerical models has been presented to evaluate the plasmonic waveguide performance. For device-level consideration, we demonstrated through simulations that Cu (1450 nm pitch) and PLD-TiN (900 nm pitch) plasmonic waveguides symmetrically sandwiched by SiO₂ with much smaller and hence denser interconnects,are promising candidates for use in global wires for the asynchronous communication. This design of plasmonic waveguide can bridge the CMOS circuitry and high-speed communication at optical frequencies within chip. For a system-level assessment, both of them have the same bandwidth throughput of∼19.8 Gbps. The other performance parameters of Cu and PLD-TiN plasmonic waveguides are respectively, signal latency of ∼0.18 ps and 0.19 ps,energy dissipation per computing bit of ∼2.5×10⁻³ fJ/bit and 3.8×10⁻³ fJ/bit, and 25% crosstalk coupling length of 155μm and 125μm. These findings suggest that plasmonic waveguide for intra-chip communication surpass those of existing electronic interconnects for all the categories of performance parameters. National Research Foundation (NRF) Published version This research was supported by National Research Foundation Singapore project of Integration of Electrically Driven Plasmonic Components in High Speed (NRF2016_CRP001_111).

The physical origin of epsilon-near-zero (ENZ) optical nonlinearity lies in the hot-electron dynamics, in which electron scattering plays an important role. With the damping factor defined by hot electron scattering time, the Drude model could be extended to modeling ENZ optical nonlinearity completely. We proposed a statistical electron scattering model that takes into account the effect of electron distribution in a nonparabolic band and conducted the investigation on indium tin oxide (ITO) with femtosecond-pump continuum-probe experiment. We found that ionized impurity scattering and acoustic phonon scattering are the two major scattering mechanisms, of which the latter had been neglected before. They dominate at low-energy and high-energy electrons, respectively, and are weakened or boosted for high electron temperature, respectively. The electron energy–dependent scattering time contributed from multiple scattering mechanisms shows the electron density–dependent damping factor. The comprehensive understanding of electron scattering in ITO will help to develop a complete model of ENZ optical nonlinearity.

To develop methods to generate, manipulate, and detect plasmonic signals by electrical means with complementary metal-oxide-semiconductor (CMOS)-compatible materials is essential to realize on-chip electronic-plasmonic transduction. Here, electrically driven, CMOS-compatible electronic-plasmonic transducers with Al-AlOX -Cu tunnel junctions as the excitation source of surface plasmon polaritons (SPPs) and Si-Cu Schottky diodes as the detector of SPPs, connected via plasmonic strip waveguides of Cu, are demonstrated. Remarkably, the electronic-plasmonic transducers exhibit overall transduction efficiency of 1.85 ± 0.03%, five times higher than previously reported transducers with two tunnel junctions (metal-insulator-metal (MIM)-MIM transducers) where SPPs are detected based on optical rectification. The result establishes a new platform to convert electronic signals to plasmonic signals via electrical means, paving the way toward CMOS-compatible plasmonic components.

Integrating multiple properties in a single system is crucial for the continuous developments in electronic devices. However, some physical properties are mutually exclusive in nature. Here, we report the coexistence of two seemingly mutually exclusive properties-polarity and two-dimensional conductivity-in ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin films at the LaAlO$_3$/Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ interface at room temperature. The polarity of a ~3.2 nm Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin film is preserved with a two-dimensional mobile carrier density of ~0.05 electron per unit cell. We show that the electronic reconstruction resulting from the competition between the built-in electric field of LaAlO$_3$ and the polarization of Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ is responsible for this unusual two-dimensional conducting polar phase. The general concept of exploiting mutually exclusive properties at oxide interfaces via electronic reconstruction may be applicable to other strongly-correlated oxide interfaces, thus opening windows to new functional nanoscale materials for applications in novel nanoelectronics., Comment: Main text: 25 pages, 4 figures Supplementary note: 19 pages, 11 figures

International audience; Electro-optic modulators are among the most important building blocks in optical communication networks. Lithium niobate, for example, has traditionally been widely used to fabricate high-speed optical modulators due to its large Pockels effect. Another material, barium titanate, nominally has a 50 times stronger r-parameter and would ordinarily be a more attractive material choice for such modulators or other applications. In practice, barium titanate thin films for optical waveguide devices are usually grown on magnesium oxide due to its low refractive index, allowing vertical mode confinement. However, the crystal quality is normally degraded. Here, a group of scandate-based substrates with small lattice mismatch and low refractive index compared to that of barium titanate is identified, thus concurrently satisfying high crystal quality and vertical optical mode confinement. This work provides a platform for nonlinear on-chip optoelectronics and can be promising for waveguide-based optical devices such as Mach-Zehnder modulators, wavelength division multiplexing, and quantum optics-on-chip.

Microring resonators, as a fundamental building block of photonic integrated circuits, are well developed into numerous functional devices, whose performances are strongly determined by microring’s resonance lineshapes. We propose a compact structure to reliably realize Lorentzian, Fano, and electromagnetically induced transparency (EIT) resonance lineshapes in a microring. By simply inserting two air-holes in the side-coupled waveguide of a microring, a Fabry-Perot (FP) resonance is involved to couple with microring’s resonant modes, showing Lorentzian, Fano, and EIT lineshapes over one free spectral range of the FP resonance. The quality factors, extinction ratios (ERs), and slope rates (SRs) in different lineshapes are discussed. At microring’s specific resonant wavelength, the lineshape could be tuned among these three types by controlling the FP cavity’s length. Experiment results verify the theoretical analysis well and represent Fano lineshapes with ERs of about 20 dB and SRs over 280 dB/nm. The reliably and flexibly tunable lineshapes in the compact structure have potentials to improve microring-based devices and expand their application scopes.

High quality GaN was grown on 200 mm Si (111) substrates by using AlN and 3 step-graded AlxGa1-xN as the buffer layer in a metalorganic chemical vapor deposition system. We have investigated the influence of NH3 pre-flow time on the threading dislocation density (TDD) of AlN, AlGaN buffer layers and GaN layers. It was observed that the compressive stress introduced into the buffer layer and GaN is dependent on the nitridation time. The lowest TDD for GaN obtained in our samples was ~1 × 109 cm−2 for screw type and 3.2 × 109 cm−2 for edge type dislocations, as obtained from atomic force microscopy and further confirmed by high resolution X-ray diffraction analysis. The threading dislocations generated in the first buffer layer (AlN) during its nucleation are found to influence the TDD in the subsequent layers. Samples without an intentional nitridation step exhibit higher TDD compared to the samples with optimal nitridation time. Longer nitridation time also leads to poor crystalline quality likely because of amorphous SiNx formation at the interface.

Two diketopyrrolopyrrole- (DPP) and thienothiophene-based donor–acceptor (D–A) type conjugated polymers are separately synthesized using Stille coupling reactions with Pd(PPh3)4 and PdCl2(PPh3)2 catalytic systems, respectively. The influence of the catalyst employed on the structural regularity of the resulting polymers, and their subsequent electrochromic (EC) performances are investigated. Marked differences in the optical contrasts, switching times, coloration efficiencies and redox stabilities of the polymers are uncovered. For example, polymer P1, which is prepared using Pd(PPh3)4 as a catalyst, exhibited a larger optical contrast and coloration efficiency by 40% and 79%, respectively, and a faster coloration time by 55%, at 825 nm, than its counterpart polymer P2, which is prepared using PdCl2(PPh3)2. The intrinsic optical, electrochemical and morphological properties of the polymers are characterized, revealing that the physical conformation and packing of the polymer chains are the main factors causing the discrepancy in EC performances.

We report on the growth of In0.30Ga0.70As channel high electron mobility transistor (HEMT) epi-layers on a 200-mm Si substrate by metal-organic-chemical-vapor-deposition. The HEMT layers were grown on the Si substrate by using a ~3- ${\mu }\text{m}$ thick epitaxial buffer composing of a Ge layer, a GaAs layer, and a compositionally graded and strain relaxed InAlAs layer. The optimized epitaxy has a threading dislocation density of less than $2 {\times } 10^{{7}}$ cm−2 and a root mean square surface roughness of ~6.7 nm. The device active layers include a ${ {\delta } }$ -doped InAlAs bottom barrier, a ~15-nm thick InGaAs channel, a ~8-nm InGaP top barrier layer and a heavily doped InGaAs contact layer. MOSHEMTs with channel length down to 130 nm were fabricated. The devices achieve a peak transconductance of ${\sim }450 ~{\mu }\text{S}/ {\mu }\text{m}$ at ${V} _{ D}$ of 0.5 V. The peak effective mobility ( ${\mu }_{\text {eff}}$ ) in a device with a channel length of 20 $ {\mu }\text{m}$ device channel was ~3700 cm2/ $\text{V} {\cdot }\text{s}$ .

Self-assembled growth of SrTi0.87Fe0.13O3−δ (STF)/ZnO vertical nanocomposite films by combinatorial pulsed laser deposition is described. The nanocomposite films form vertically aligned columnar epitaxial nanostructures on SrTiO3 substrates, in which the STF shows room-temperature magnetism. The magnetic properties are discussed in terms of strain states, oxygen vacancies, and microstructures. The nanocomposites exhibit magneto-photoluminescent coupling behavior that the near-band-edge emission of ZnO is shifted as a function of magnetic field.

Broadband antireflection coatings for terahertz (THz) components are extremely important in the application of THz technology. We present an in-depth materials study on the broadband antireflection design based on the concept of impedance matching. Several selected conductive materials are tested and compared. They can all be used as THz broadband antireflection coatings regardless of their nature of conductivity. We provide a facile method to approximately predict the impedance matching condition for various conductive materials based on their dc real conductivity. The theoretical predications are in good agreement with experimental results and published data. Doped metal oxides or polymers are recommended as good candidates for fabricating antireflection coating in THz range. The thickness-independent dc real conductivity enables better control on individual tuning parameter—film thickness. Given a substrate, THz transmission in antireflection coating has a theoretical upper limit which is further reduced with non-negligible imaginary conductivity.

To improve the bonding yield and the brightness of the final integrated Si-CMOS + GaN LED wafers, two issues have to be addressed. The first problem is the surface protrusions such as melt-back etching and hillocks which are the common surface imperfections on the surface of GaN/Si substrates. This prevents the direct contact of the two wafers and results in unbonded area. To address this, a CMP process that using conventional SiO 2 slurry with the addition of diamond nanoparticles is carried out on the GaN (LED)-on-Si wafer prior to the bonding to the Si-CMOS wafer. The second issue is that the Si substrate of the GaN LED wafer absorbs photons which lowers the light emitting efficiency of the LEDs. We address this issue by transferring the Si-CMOS + GaN LED films from the Si (111) wafer onto a transparent quartz substrate. By addressing these issues, a high bonding yield and high brightness of Si-CMOS + GaN LED on quartz substrate can be realized.

Plasmonic nanocavities enable extreme light-matter interaction by pushing light down to the nanoscale. The dipolar feature of bright modes allows coupling with the external excitation from free space but results in a radiating background, whereas nonradiating dark plasmon modes can hardly be excited. Here, we report for the first time on strong coupling between dark plasmon and anapole modes in a hybrid metal-dielectric nanostructure. With the aid of vanishing dipole characteristics of the anapole and dark plasmons, the hybrid modes exhibit minimum far-field scattering and maximum near-field enhancement. The dark mode coupling in the metal-dielectric nanostructure offers a nonradiating air cavity with greatly improved field enhancement in a broadened band, thus providing a background-free experimental platform for spectroscopic applications. The proposed approach to dark plasmon excitation, i.e., via anapole, may boost practical exploitation of dark plasmons by allowing linearly polarized light illumination and scalable arrays of individual nanostructure units.

Optical nonlinearity due to intraband transitions (which is important for the application of epsilon-near-zero nonlinearity in metasurfaces and active plasmonics) requires a model to fully predict the spectrum, for design considerations. The extended Drude model, presented here, serves this purpose. It further elucidates the origin of the nonlinearity to be due to both band nonparabolicity and temperature-dependent mobility. The model matches experiment well for the representative compound indium tin oxide, and simplifies the description of spectrally resolved optical nonlinearities of transparent conductive oxides.

Tandem solar cells consisting of perovskite and silicon sub-cells are very promising for low-cost electricity generation due to low fabrication cost and high efficiency potential. Due to the limited active area of perovskite top cells available at the moment, the fabrication of small-area passivated contact n-type monoPolyTM silicon solar cells customized for tandem applications is investigated by scaling down from 6-inch full-size solar cells fabricated using industrial tools. The directly fabricated small-area silicon solar cells have an efficiency of 33% for the wavelength range 750 - 1100 nm of the AM1.5G solar spectrum. By optimizing both perovskite and silicon sub-cells, an energy conversion efficiency of 24.9% was achieved for perovskite on silicon four-terminal tandem cells.

To improve the bonding yield and the brightness of the final integrated Si-CMOS + GaN LED wafer, two issues need to be addressed. The first problem is the surface protrusions such as melt-back etching and hillocks which are the common surface imperfections on the surface of GaN/Si substrates. This prevents the direct contact of the two wafers and create unbonded area. To address this, a CMP process that using conventional SiO 2 slurry with additional diamond nanoparticles is carried out on the GaN (LED)-on-Si wafer prior to the bonding to the Si-CMOS wafer. The second issue is the Si substrate of the GaN LED wafer absorbs photons which lowers the light emitting efficiency of the LEDs. We address this issue by transferring the Si-CMOS + GaN LED films from the Si (111) wafer to a transparent quartz substrate. By addressing these issues, a high bonding yield and high brightness of Si-CMOS + GaN LED on quartz substrate is realized.

Thermal nanoimprint lithography was utilized as an efficient method to directly create periodic nanostructures on the conjugated polymer films that were synthesized from 2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, 3,3-bis((tetradecyloxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine and thieno[3,2-b]thiophene monomers. This type of nanopatterned polymer film with 275 nm features was achieved by the use of a direct, top-down thermal nanoimprinting method, and then fabricated into absorption/transmission type electrochromic devices. The nanopatterned devices displayed considerably better overall electrochromic performance than their non-nanostructured pristine counterpart as evidenced by the improvement of up to 20% in switching speed, coloration efficiency as well as enhanced colored-to-transmissive optical contrast. The improvement in electrochromic performance could be ascribed to the increased exposed polymer surface area induced upon nano-structuring of the conjugated polymer films, which was demonstrated by the fact that the increase in the imprint depth from 100 to 130 nm led to a further improvement in the electrochromic performance such as shorter switching speeds and higher coloration efficiency. In addition, unlike the pristine un-patterned polymer film which displays an identical hue regardless of the viewing angle, the nanoimprinted films gave different hues under different viewing angles because of the ability of the nanogratings to diffract ambient white light, potentially opening up the path to many interesting applications.

The growth of Gallium nitride on sapphire substrate generated a high density of threading dislocations in the order of ~108-109 /cm2. In this work, porous GaN template with different pore sizes was generated using Anodized Alumina oxide mask prepared by anodization with set voltage ranging from 40 V to 100V. Inductive coupled plasma etching generated porous GaN using the oxide mask. The etched pores have an estimated depth of 150 nm and the pores diameter range from 35 nm to 150 nm. Regrowth of GaN with embedded air voids provide a strain relaxed overgrown GaN layer with dislocation annihilation at the voids region. High resolution X-ray rocking curves at the symmetrical plane (002), (004) and (006) was obtained for the overgrown GaN demonstrate a significant reduction in FWHM for overgrown GaN on porous GaN template as compared to conventional GaN template. Dislocation density reduction estimated using Ayer model revealed an order of magnitude reduction of screw and mixed dislocation to higher order of 107cm-2 for overgrown on porous GaN with size of 70 nm to 100nm. Pits density counts which can be correlated to threading dislocations in the materials shows that the regrowth GaN samples on strain relief GaN has an order of magnitude lower pits density as compared to that conventional GaN sample.

Deep level traps in the low dislocation density, 5.1 × 107 cm−2, semi-polar GaN (11–22), grown on patterned sapphire substrate was characterized for the first time using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS). DLTS revealed two deep levels ET1 = EC − 0.24 eV and ET2 = EC − 0.41 eV in the semi-polar GaN layer. The dominant trap ET1 = EC − 0.24 eV with a density of 6.1 × 1014 cm−3, is documented in c-plane and m-plane GaN. It is attributed to VN. DLOS revealed two deep level traps ET3 = EC − 1.20 eV and ET4 = EC − 3.26 eV. The dominant level ET4 = EC − 3.26 eV is also observed in non-polar m-plane GaN grown on sapphire and it is attributed to CN acceptor-like state. The total trap density of the semi-polar GaN is about 2 × 1016 cm−3, which is comparable with that found in c-plane GaN.

Graphene nano-ribbon waveguides with ultra-short plasmon wavelength are a promising candidate for nanoscale photonic applications. Graphene edge plasmons are the fundamental and lowest losses mode. Through finite element method, edge plasmons show large effective refractive index and strong field confinement on nanoscale ribbons. The edge plasmons follow a k 1/2 dispersion relation. The wavelengths of the edge plasmons and center plasmons differ by a fixed factor. The width of edge plasmon is inversely proportional to wave vector of edge plasmon k edge . Edge defects associate with graphene nano-ribbon induce extra losses and reduce the propagation length. Cut-off width of edge plasmons reduces with increasing frequency. Cut-off width of center plasmon is enlarged by edge component but the enlargement effect diminishing with the increase of k edge . The results are important for the application of graphene plasmon towards ultra-compact photonic devices.

In this investigation, we report an Au/Si hot electron infrared detector fabricated on an SOI substrate. The simulation and experimental results show that Fabry–Perot cavity resonance on the SOI substrate and the surface plasmons excited by the Au nanostructures enhance the photo absorption in Au. Spectral response peaks of the hot electron photocurrent occur in the infrared band at a photon energy much smaller than the bandgap energy of Si. A maximum photocurrent was obtained at an annealing time of 90 s of the nanostructured Au film, and the SEM image showed the formation of a connected semi-island structure during the annealing. This hot electron device paves the way for extending infrared detection wavelength of SOI based detectors.

Light emission from inelastic electron tunneling has been demonstrated for 40 years. The ultrafast response rate and the ultracompact footprint make it promising for high-speed miniaturized light sources. But the application of the tunnel junction is limited by extremely low external quantum efficiency due to the low proportion of inelastic tunneling electron and wave vector mismatch between surface plasmons and photon emission. Here, we present a plasmonic-enhanced metal-insulator-semiconductor (MIS) junction coupled to a silicon waveguide with a coplanar electrode connected to a nanoantenna. The proposed tunnel junction can be fabricated using existing semiconductor planar processes to achieve controllable barrier thickness and quality for vertical current injection. Finally, an electrically driven light source with a radiation power nearly 8000 times higher than the spontaneous emission power in free space is shown to be achievable with the new structure at an operating wavelength of 1.31 µm. It is 510-fold higher than that of typical planar MIS junctions.

Plasmonic color filters are expected to be candidates for application to complementary metal–oxide–semiconductor (CMOS) image sensor arrays with reduced pixel size, owing to the subwavelength mode volume of plasmons. Designs of metallic gratings based on the guided-mode resonance effect suffer from the sideband transmission issue due to high-order diffraction. Here, we propose a plasmonic color filter structure based on a hetero-metal-insulator-metal grating. The guided mode, in resonance with the second-order diffraction, is highly attenuated by the forbidden band, such that the sideband transmission can be suppressed. As calculated by using the transfer matrix method and the finite-difference time-domain method, the Al-ZnO-Ag waveguide-based structure presents a color filter characteristic with the peak transmittance greater than 70% and the peak wavelength tunable in the visible light band. It may find application in displays, image sensors, and biomedical imaging technologies.

We report an aluminum nitride on insulator platform for mid-infrared (MIR) photonics applications beyond 3 μm. Propagation loss and bending loss are studied, while functional devices such as directional couplers, multimode interferometers, and add/drop filters are demonstrated with high performance. The complementary metal-oxide-semiconductor-compatible aluminum nitride offers advantages ranging from a large transparency window, high thermal and chemical resistance, to piezoelectric tunability and three-dimensional integration capability. This platform can have synergy with other photonics platforms to enable novel applications for sensing and thermal imaging in MIR.

A plasmon-induced hot-electron photodetector based on silicon nanopillar array is developed. The nanostructure is fabricated by reactive ion etching with a monolayer of self-assembled polystyrene nanosphere in hexagonal close-packed lattice as the mask. Light absorption and hot-electron generation are mainly enhanced by the surface plasmon polaritons formed at the surface of the gold film on the nanopillar sidewalls. The photoresponse spans two telecom wavebands, viz. the range of 1250-1600 nm, and has a value of 2.5 mA W-1 at 1310 nm. The proposed silicon nanopillar-based hot-electron infrared detector has great potentials for device integration in silicon photonics relying on the economic large-area fabrication process.

Leveraging on plasmonic hot electrons is regarded as an emerging strategy for electron–hole separation toward efficient photovoltaics and photocatalysis, but its application in electron–hole recombination for illumination is rarely explored. Herein, a significantly improved ultraviolet luminescence is reported from Cu-doped ZnO nanowires (NWs) through dopant mediated generation and transfer of plasmonic hot electrons. Through coupling the Cu dopants-correlated green luminescence in Cu-doped ZnO NWs with the localized surface plasmon resonance of Au nanoparticles (NPs), UV emission from the NWs is enhanced by a factor of ≈280 and its lifetime drops from 2.45 ns to about 18 ps after covering the NWs with Au NPs. Moreover, robust UV emission sustains from room temperature to low temperature. This work extends the applications of plasmonic hot electrons and provides an appealing route toward achieving intense, ultrafast, and temperature-robust luminescence, which holds great potential in light-emitting diode and laser diodes for illumination, optical communication, and biomedical applications.

In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In0.1Ga0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al0.2Ga0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.

The research on electrochromic conjugated polymers (ECPs) and their devices has gone a long way. They can now perform with a multitude of color variations, high optical contrasts, rapid switching speeds and low power consumption. This review traces the progress of color control, synthetic methods, and the development of building blocks for ECPs. The advances in the integration and optimization of electrochromic devices (ECDs) in terms of their constituting components are presented. The potential of ECDs in numerous applications through the illustration of several prototypes is then highlighted. Finally, the challenges associated with the prospective commercialization of the said devices are discussed.

During recent years, Terahertz (THz) electronics has attracted much attention in the applications of medical, biological and industrial imaging, broadband communication etc. A GaN high-electron-mobility transistor (HEMT) is promising to work as a THz detector due to its high breakdown field, high carrier density and high temperature operation ability etc. Here we report a quasistatic self-mixing model to describe the main features of the THz response in a GaN HEMT. The model can explain not only the magnitude, but also the polarity of the photocurrent. Based on this model, we improve the gate design in GaN HEMTs from traditional symmetric pads to novel asymmetric pads. This novel gate design has been proved to be able to improve the THz detection responsivity by one order of magnitude.

Neutral-state black diketopyrrolopyrrole (DPP)-based conjugated polymers with the colour channels a* from −3 to 0 and b* from −2 to −7 are achieved by incorporating an additional donor segment – dialkoxythiophene (DalkOT), which leads to the enhancement in blue-wavelength absorption. The polymers display black-to-transmissive grey electrochromic switching with good redox stability.

InGaN/Si multijunction solar cells form a cost-effective approach for full-spectrum photovoltaics. However, heteroepitaxial InGaN films with high In content are highly defective. To overcome this, nanostructured InGaN growth is explored in this work. Ordered arrays of In x Ga 1− x N nanopyramids were grown by metalorganic chemical vapor deposition on AlN(0001)/Si(111) substrates in a selective area heteroepitaxy approach. The effect of growth temperature and pressure on the morphology, structure and photoluminescence of the nanopyramids, and their In content x were studied. Reduction in temperature increases x but temperatures x can be improved. This also enhances the growth rate and improves nanopyramid size uniformity. Nanopyramid arrays generally exhibit greater lattice tilt than their control films due to dislocation bending. While lattice twist is increased with higher x , it is offset by epitaxial lateral overgrowth. Compared to control films, nanopyramid samples consistently yielded higher x , lower average reflectance (

A series of 4,9-dihydro-s-indecano[1,2-b:5,6-b’]dithiophene containing conjugated polymers with thiophene, 2,2׳-bithiophene, and thieno[3,2-b]thiophene as co-monomers was synthesized through Stille coupling reaction with good yields as well as high molecular weights. The physical and electrochemical properties of the resulting polymers were fully characterized. The polymers displayed exceptional solubility in common organic solvents. The polymers were fabricated as the electrochromic layer in absorption/transmission type electrochromic devices. Upon oxidation, the polymer films switched from a dark red to a grayish hue, displaying optical contrasts of about 20% and 40% in the visible and near-infrared (NIR) regions respectively, as well as reasonable ambient stabilities. In particular, the polymers exhibited rapid sub-second coloration times with exceptionally high coloration efficiencies of up to 1066 cm2/C in the visible region. Contrary to the traditional electrochromic conjugated polymers that typically show prolonged optical memory, these polymers exhibited a tendency to quickly lose their optical memory.

GaN-on-Silicon growth by MOCVD is wildly discussed in the context of stress and strain management. The low bow AlGaN/GaN structure grew on 200mm Si(111) wafer was demonstrated in this study. After using the sapphire pits on the normal flat susceptor, the wafer bow and residual stress decrease to 21.27um and 0.28GPa tensile stress. The GaN quality and the Rs in HEMT also got huge improvement. The sub-micron devices also show the comparable results in DC and small signal characteristics.