Semiconductor Metamaterials Research Articles

A brief report on nanophotonics and metamaterials landscape in India

AbstractHere, we describe a set of research results in the domain of Nanophotonics and Metamaterials that represent the broad N &M landscape in India. These results were presented in an online BRICS meeting, and were collated based on the criteria deemed appropriate for the said forum. Results presented at the meeting encompass various areas, including nano-optics, nano-opto-mechanics, integrated photonic devices, plasmonics, metal-enhanced fluorescence, bio relevant photonics and metamaterials. Research topics such as Anderson localization of light, exceptional points in non-Hermitian systems, manipulation of nanoscale mechanical motion, efficient mode coupling in integrated photonics etc are discussed. Furthermore, miniaturized SPR sensors, coupling between metal nanostructures and semiconductor quantum dots, biosensing applications, metamaterials and random lasing, and customizable optical functionalities for sensing, and energy conversion are also elaborated upon. In the end, a brief listing of more recent selected publications is presented. This review article highlights the diverse and promising avenues in nanophotonics and metamaterials research in India.

Topological Darkness: How to Design a Metamaterial for Optical Biosensing with Ultrahigh Sensitivity.

Due to the absence of labels and fast analyses, optical biosensors promise major advances in biomedical diagnostics, security, environmental, and food safety applications. However, the sensitivity of the most advanced plasmonic biosensor implementations has a fundamental limitation caused by losses in the system and/or geometry of biochips. Here, we report a "scissor effect" in topologically dark metamaterials which is capable of providing ultrahigh-amplitude sensitivity to biosensing events, thus solving the bottleneck sensitivity limitation problem. We explain how the "scissor effect" can be realized via the proper design of topologically dark metamaterials and describe strategies for their fabrication. To validate the applicability of this effect in biosensing, we demonstrate the detection of folic acid (vitamin important for human health) in a wide 3-log linear dynamic range with a limit of detection of 0.22 nM, which is orders of magnitude better than those previously reported for all optical counterparts. Our work provides possibilities for designing and realizing plasmonic, semiconductor, and dielectric metamaterials with ultrasensitivity to binding events.

Narrow Linewidth Terahertz Filter Based on Gold-Coated Polymer Plates With Corrugations

Terahertz (THz) devices, especially for narrowband filters, have been widely investigated over the past decades, but mostly based on semiconductor materials or metamaterials. Here, we experimentally and numerically demonstrate a waveguide-type narrowband THz filter, which is realized by two parallel plates with corrugations. The corrugated plates are fabricated by sputtering a layer of gold after laser ablation of polymer sheets. The laser periodically etches the groove and produces a wide groove in the middle, which destroys the periodicity of the structure and forms a defect. The periodicity provides a forbidden band, in which THz waves cannot propagate, and the defect leads to an additional transmission in the forbidden band. This additional transmission occurs in the middle of the gap and has a very narrow linewidth, which is a good candidate for THz filtering. The achieved linewidth and the extinction ratio are about 1.5 GHz and 29 dB, respectively, limited by our experimental system, which are further optimized in numerical simulations. The proposed fabrication method is very efficient in THz waveguide devices, which can be easily integrated in applicable THz systems.

On the Study of Advanced Nanostructured Semiconductor-Based Metamaterial

Tunable metamaterials belonging to the class of different reconfigurable optical devices have proved to be an excellent candidate for dynamic and efficient light control. However, due to the consistent optical response of metals, there are some limitations aiming to directly engineer electromagnetic resonances of widespread metal-based composites. The former is accomplished by altering the features or structures of substrates around the resonant unit cells only. In this regard, the adjusting of metallic composites has considerably weak performance. Herein, we make a step forward by providing deep insight into a direct tuning approach for semiconductor-based composites. The resonance behavior of their properties can be dramatically affected by manipulating the distribution of free carriers in unit cells under an applied voltage. The mentioned approach has been demonstrated in the case of semiconductor metamaterials by comparing the enhanced propagation of surface plasmon polaritons with a conventional semiconductor/air case. Theoretically, the presented approach provides a fertile ground to simplify the configuration of engineerable composites and provides a fertile ground for applications in ultrathin, linearly tunable, and on-chip integrated optical components. These include reconfigurable ultrathin lenses, nanoscale spatial light modulators, and optical cavities with switchable resonance modes.

Understanding and Control of Compressively Buckled Semiconductor Thin Films

We report the controllable buckling of free-standing thin-film semiconductor metamaterials using a thin-walled structure spanning $\mathrm{Au}$ grid supports. The buckling is developed by compressing the $\mathrm{Au}$ grids, increasing the internal air pressure during the bonding of $\mathrm{Au}$ pads on the semiconductor to the grids, resulting in upward deformation. The stiffness of the free-standing semiconductor beam is controlled by the grid line spacing, as verified for a wide range of out-of-plane deformations, ranging from nearly flat to microns for grid line spacings from 20 to 150 \textmu{}m, respectively. We also observe telephone-cord and domelike buckling as the grid line spacings and layer thicknesses are varied. Finite element analysis quantitatively predicts the shape and magnitude of the film deflection. We propose strategies to apply the distorted free-standing metamaterials for thermal energy harvesting, optical reflectors, and pressure sensors.

Applications of chip-scale semiconductor metamaterials based on plasmon-induced transparency in modulation and sensing

We propose and simulate the tunable plasmon-induced transparency (PIT) phenomenon of semiconductor-based H-shaped chip-scale metamaterials. Numerical analysis shows that the PIT phenomenon is caused by the destructive interference between two bright modes, and the equivalent Lorentz model also proves its physical mechanism appropriately. In addition, in practical applications, changing the polarization angle can adjust the group delay, and the maximum group delay is 41.92 ps; changing the temperature can adjust the transmission peak frequency of the PIT effect, which can be applied to temperature sensing and thermo-optic switches. The amplitude modulation depth can reach 97.8%. The application of this chip-scale semiconductor metamaterial in modulators and sensors opens up new ways.

Investigation of tunable Fano resonances based on the InSb metamaterials

Based on the hybrid semiconductive InSb metamaterials (MMs), we investigated the tunable Fano resonances in the terahertz regime, including the effects of carrier concentrations of InSb layer, environment temperatures and operation frequencies. The results manifested that an obvious Fano resonance was observed by using the heterostructure of InSb bars, the peak value of Fano resonance reached more than 0.97 with a high [Formula: see text]-factor of larger than 50. By changing the carrier concentrations of InSb layer, the propagation properties of semiconductor MM structures can be effectively modulated, the amplitude modulation of Fano resonance can reach more than 80%. The results are helpful for designing novel tunable terahertz devices with high [Formula: see text]-factor, e.g. modulators, sensors and antenna.

A novel graphene based tunable semiconductor metamaterial: A mathematical analysis

Abstract. In this article we have proposed a novel graphene based tunable semiconductor metamaterial which can be effectively tuned in the long wavelength infrared region of the electromagnetic spectrum by only changing the chemical potential of graphene via a gate voltage without needing to vary the doping concentration of semiconductor. The previously reported semiconductor metamaterial constructed from doped InGaAs and intrinsic AlInAs layers shows all angle negative refraction Hoffman et al.. However, it cannot be tuned without changing the doping concentration of semiconductor and changing doping concentration makes the material lossy. Since Graphene possesses tunable surface conductivity which can be tuned effectively by changing the chemical potential of graphene, we have proposed a novel structure where graphene sheet is inserted between the InGaAs and AlInAs layers. Through rigorous mathematical analysis we have shown that by changing only the chemical potential, without needing to modify the structural properties, it is possible to tune the spectral region of permittivity where negative refraction occurs which in turns gives tunability to iso-frequency wave vector dispersion, transmittance, reflectance and absorption coefficient. The proposed method would simplify the tuning process of semiconductor metamaterials. This unique graphene based tunable semiconductor metamaterial would be an attractive feature in the rapid and continuously developing semiconductor industry.

High sensitivity refractive index and temperature sensor based on semiconductor metamaterial perfect absorber in the terahertz band

We propose theoretically and numerically a highly sensitive refractive index and temperature sensor based on semiconductor metamaterials in the terahertz range. We demonstrate that the metamaterial sensor is a perfect absorber which absorption rate is 99.9% and because of including a square-shaped ring has a remarkable feature that is polarization independent of the incident light. The perfect absorber can be operated as a refractive index sensor with a sensitivity of 146600 nm/RIU. More importantly, the perfect absorber can be operated as a temperature sensor with a sensitivity of 7144 nm/K. The metamaterial structure has considerable potential in the chemical and biological applications because of having a high resolution.

Direct-tuning methods for semiconductor metamaterials

Among various tunable optical devices, tunable metamaterials have exhibited their excellent ability to dynamically manipulate lights in an efficient manner. However, for unchangeable optical properties of metals, electromagnetic resonances of popular metallic metamaterials are usually tuned indirectly by varying the properties or structures of substrates around the resonant unit cells, and the tuning of metallic metamaterials has significantly low efficiency. In this paper, a direct-tuning method for semiconductor metamaterials is proposed. The resonance strength and resonance frequencies of the metamaterials can be significantly tuned by controlling free carriers’ distributions in unit cells under an applied voltage. This direct-tuning method has been verified in both two-dimensional and three-dimensional semiconductor metamaterials. In principle, the method allows for simplifying the structure of tunable metamaterials and opens the path to applications in ultrathin, linearly-tunable, and on-chip integrated optical components (e.g., tunable ultrathin lenses, nanoscale spatial light modulators and optical cavities with resonance modes switchable).

Circularly polarized light detection using chiral hybrid perovskite

Circularly polarized light (CPL) detection is required in various fields such as drug screening, security surveillance and quantum optics. Conventionally, CPL photodetector needs the installation of optical elements, imposing difficulties for integrated and flexible devices. The established CPL detectors without optical elements rely on chiral organic semiconductor and metal metamaterials, but they suffer from extremely low responsivity. Organic-inorganic hybrid materials combine CPL-sensitive absorption induced by chiral organics and efficient charge transport of inorganic frameworks, providing an option for direct CPL detection. Here we report the CPL detector using chiral organic-inorganic hybrid perovskites, and obtain a device with responsivity of 797 mA W-1, detectivity of 7.1 × 1011 Jones, 3-dB frequency of 150 Hz and one-month stability, a competitive combined feature for circularly polarized light detection. Thanks to the solution processing, we further demonstrate flexible devices on polyethylene terephthalate substrate with comparable performance.

Thermo-optical applications of a novel terahertz semiconductor metamaterial design

In this paper, a novel semiconductor metamaterial design based on electronically induced reflection is proposed, and its thermo-optic applications at the terahertz frequency are investigated. The analytical results show that the peak resonance wavelength position depended very sensitively on the temperature of the structure. The room-temperature operation up to 9 μmK at T=295 K is achieved, which is more than the other values in the literature. It is also shown that by increasing the temperature, the emission decreases, which is promising for thermal regulation, thermal tagging, and labeling applications. Furthermore, we demonstrate numerically that the thermal modulating application can be realized in the proposed semiconductor metamaterial. We achieved 15.4% for the modulation depth and 5.14% for the amplitude modulation depth, which are great values. In general, the work has numerically proved that the thermo-optical design used has very good prospects for various negative differential thermo-optic emission technologies. Furthermore, this semiconductor-based metamaterial structure can develop a path in narrow-band thermo-optic modulating and sensing applications and the like in the future.

Optimization of cubic GaN/AlGaN quantum cascade structures for negative refraction in the THz spectral range

In this work we theoretically investigate a possibility to use cubic nitride based multi-layer periodic nanostructure as a semiconductor metamaterial. The structure design is based on an active region of a quantum cascade laser optimized to achieve optical gain in the Terahertz (THz) spectral range. In particular, we test the GaN/AlGaN quantum well configurations, which should exhibit important advantages compared to GaAs-based structures, namely room temperature operation without the assistance of magnetic field and lower doping densities. Our numerical rate-equations model is solved self-consistently and it takes into account electron-longitudinal optical phonon scattering between all the relevant states among the adjacent periods of the structure. A global optimization routine, specifically genetic algorithm is then used to generate new gain-optimized structures. This work confirms the advantages of cubic GaN designs over GaAs ones, namely feasibility of negative refraction at room temperature without the assistance of magnetic field while keeping the doping densities of the same order of magnitude.

Intersubband plasmons induced negative refraction at mid-IR frequency in heterostructured semiconductor metamaterials

In this contribution, we report on negative refraction effect occurring in layered semiconductors. The origin of this effect is attributed to the presence of intersubband plasmon resonance induced by the electronic confinement of the electrons in thick quantum wells. Relying on the effective medium theory, we analyse both the in plane and the out of plane effective optical properties of highly doped ZnO/ZnMgO semiconductor material. We theoretically show and experimentally demonstrate that thicknesses and doping levels of each layer can be carefully chosen to feature strong intersubband transitions, leading to type 1 and type 2 hyperbolic response. Understanding the optical properties of intersubband materials in the frame of hyperbolic materials would shed new light on which physical mechanisms are controlling the radiative decay of intersubband plasmon excitations. This approach could be further utilized to designing efficient mid-IR sources.

Investigation of graphene-supported tunable asymmetric terahertz metamaterials

By integrating a graphene layer with asymmetric split-ring metamaterial (MM) metal resonators, we investigated tunable propagation properties in the terahertz regime, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that a sharp inductor-capacitor (LC) resonance can be observed at low frequency for the asymmetric MM structure, and its Q factor can reach more than 17.5. With the help of a graphene layer, the optical response is modulated efficiently. For instance, if the Fermi level changes in the range of 0.01–0.3 eV, for the semiconductor MM structure, the modulation depths (MDs) of amplitude and frequency are 27.0% and 43.4%, respectively. In addition, the resonant curves of indium antimonide (InSb) MMs can be modulated by changing the temperature; the amplitude MD is 56.2% as the temperature changes in the range of 350–800 K. The Q factor of the InSb MM structure is about 44.6. The results are helpful for designing novel graphene-based tunable terahertz devices, e.g., filters and modulators.

Ultra low-loss super-resolution with extremely anisotropic semiconductor metamaterials

We investigate the mechanisms for the reduction of losses in doped semiconductor multilayers used for the construction of uniaxial metamaterials and show that maximizing the mean scattering time of the doped layers is key to spectrally isolating losses and maximizing anisotropy. By adjusting the layer thickness ratio of the multilayer, we show that the spectral regions of extreme anisotropy can be separated from those of high loss. Using these insights and coupled with realistic semiconductor growth parameters, we demonstrate an InAs-based superlens with an excellent loss factor α ≈ 52mm-1 and maximum perpendicular permittivity, ε⊥ > 250. By tuning the doping concentration, we show that such a system can be designed to operate anywhere in the region λ0 ≈ 5 to 25μm. We find that such a structure is capable of deep sub-wavelength imaging (< λ0/15) at superlens thicknesses up to ∼85μm (∼8λ0).

Surface waves supported by the nanostructured semiconductor metamaterials

We discover a new kind of surface wave on semiconductor nanostructured metamaterial, which crosses the light line with a substantial portion at lower frequencies lying above the free space light line. Interestingly, the propagation of such surface wave is found to be sensitive to the parameters of the semiconductor. Furthermore, the Ferrel-Berreman modes are observed under the certain conditions, opening a gateway toward device fabrications.

Goos–Hänchen effect in semiconductor metamaterial waveguide and its application as a biosensor

We investigate Goos–Hanchen (GH) effect in a prism waveguide coupling structure with semiconductor metamaterial (SMM) of ZnGaO/ZnO multilayer and explore the possibility as a biosensor. The GH effect in three different waveguides and their performances as a refractive index sensor to detect glycerol concentration in water are analyzed. The SMM brings a periodic property of GH shift peaks which is not found in other waveguides. It is also verified that setting coupling layer of the prism waveguide coupling structure as sensing area is an effective method to significantly increase the sensitivity to refractive index variation. A schematic diagram for the biosensor configuration is designed, and the sensitivity distribution for different glycerol water index is given. Calculation results show that in the proposed biosensor the maximum sensitivity reaches 3.2 × 106 μm/RIU and resolution reaches 1.6 × 10−7 (around 1.33306) with high sensitive position sensitive detector.

Near-Infrared Multichannel Filter in a Finite Semiconductor Metamaterial Photonic Crystal

A near-infrared (NIR) multichannel filter based on the use of a finite 1-D semiconductor metamaterial (MTM) photonic crystal (PC) is proposed. We consider a PC $\mathrm{air}/(\mathrm{AB})^{N}/\mathrm{air}$ , where $N$ is the stack number, A is a dielectric layer, and B is a semiconductor MTM made of Al-doped ZnO (AZO) and ZnO. Resonant transmission peaks can be found in the frequency region where the permittivity of AZO/ZnO is negative. It is found that the channel number is equal to $N-1$ for a given $N$ and that resonant channels are located in a passband of the photonic band structure. Additionally, the channel positions are tunable, i.e., they can be tuned by the thicknesses of A and B, the filling factor of AZO, and the incidence angle as well. The design of NIR tunable multichannel filter is of technical use for semiconductor optoelectronics.

Dual Metamaterial With Large Birefringence

Strong birefringence and a large phase delay are highly desirable for high-efficiency and compact wave plates. In order to enhance the phase delay, we combine a semiconductor metamaterial (SMM) and split-ring resonators (SRRs) into a novel dual metamaterial, which exhibits two types of resonance response, i.e., one type is mainly induced by the SMM for one polarization component of the incident wave, and the other is mainly induced by the SRRs for the other orthogonal polarization component. The unique resonance characteristics lead to large birefringence and, hence, a considerable phase delay, enabling the realization of a very compact quarter-wave plate in the middle-infrared spectrum. The concept of the dual metamaterial has the potential for developing ultracompact high-performance microoptical/nanooptical components.