Semiconductor Sources Research Articles

Nanoring Tamm cavity in the telecommunications O band

Quantum and classical telecommunications require efficient sources of light. Semiconductor sources, owing to the high refractive index of the medium, often exploit photonic cavities to enhance the external emission of photons into a well-defined optical mode. Optical Tamm States (OTSs) in which light is confined between a distributed Bragg reflector and a thin metal layer have attracted interest as confined Tamm structures are readily manufactureable broadband cavities. Their efficiency is limited however by the absorption inherent in the metal layer. We propose a nanoring Tamm structure in which a nanoscale patterned annular metasurface is exploited to reduce this absorption and thereby enhance emission efficiency. To this end, we present designs for a nanoring Tamm structure optimized for the telecommunications O band and demonstrate a near doubling of output efficiency (35%) over an analogous solid disk confined Tamm structure (18%). Simulations of designs optimized for different wavelengths are suggestive of annular coupling between the Tamm state and surface plasmons. These designs are applicable to the design of single photon sources, nano-LEDs, and nanolasers for communications.

Performance Investigation of 17 Level Reduced Switch Count Multilevel Inverter

The primary objective of this paper is to introduce a 17-level multilevel inverter with only eight power switches and three diodes that can be suitable for electric vehicle applications. This setup utilizes three distinct unequal DC sources to create the 17 levels of output voltage waveforms. The modes of operations of the proposed topology have been discussed in detail. The calculation of conduction losses, switching losses, efficiency, total standing voltage, and cost function per level for the suggested inverter has been elaborated. Due to more semiconductor power switches, diodes, capacitors, driver circuits, and DC sources in typical inverters, switching losses, costs, and harmonic distortion are increased. The nearest-level control technique has been utilized to control the switching elements of the recommended configuration. The performance comparison of various multilevel inverter topologies has also been discussed. The suggested multilevel inverter provides a higher efficiency of 98.60%, cost function of 3.6 for a weight coefficient of 1, improved power quality, and higher reliability. A reduction in the power switches significantly reduces the convolution of switching circuitry. The total harmonic distortion produced by this inverter is 3.49%, which comes under the IEEE standard of 5%.

High-rate intercity quantum key distribution with a semiconductor single-photon source

Quantum key distribution (QKD) enables the transmission of information that is secure against general attacks by eavesdroppers. The use of on-demand quantum light sources in QKD protocols is expected to help improve security and maximum tolerable loss. Semiconductor quantum dots (QDs) are a promising building block for quantum communication applications because of the deterministic emission of single photons with high brightness and low multiphoton contribution. Here we report on the first intercity QKD experiment using a bright deterministic single photon source. A BB84 protocol based on polarisation encoding is realised using the high-rate single photons in the telecommunication C-band emitted from a semiconductor QD embedded in a circular Bragg grating structure. Utilising the 79 km long link with 25.49 dB loss (equivalent to 130 km for the direct-connected optical fibre) between the German cities of Hannover and Braunschweig, a record-high secret key bits per pulse of 4.8 × 10−5 with an average quantum bit error ratio of ~ 0.65% are demonstrated. An asymptotic maximum tolerable loss of 28.11 dB is found, corresponding to a length of 144 km of standard telecommunication fibre. Deterministic semiconductor sources therefore challenge state-of-the-art QKD protocols and have the potential to excel in measurement device independent protocols and quantum repeater applications.

Phosphides‐Based Terahertz Quantum‐Cascade Laser

Due to their high optical phonon energies GaInP/AlGaInP heterostructures are a promising active medium to solve the problem of creating compact semiconductor sources with an operating frequency range of 5.5–7 THz. In this work, the temperature dependences of gain and absorption at 6.4–6.9 THz have been calculated for a GaInP/AlGaInP‐based quantum‐cascade laser (QCL) with two quantum wells in the cascade and a metal–metal waveguide. The dielectric function and mode losses for a 10 μm thick Au–Au waveguide, based on ternary InGaP and quaternary AlGaInP semiconductors, have been investigated in details. A laser structure that provides a mode gain of over 100 cm−1 with a maximum operating temperature about 100 K is proposed. The results of this study open the way to the development of a QCL for operation in a significant part of the GaAs phonon absorption band region, which is inaccessible for existing QCLs.

High-resolution X-ray diffraction to probe quantum dot asymmetry

The symmetry of nanostructures forming an active part of optoelectronic devices severely impacts their properties. It is crucial for the design of polarization-insensitive semiconductor optical amplifiers or sources of entangled photon pairs. We show how quantum dot symmetry can be measured, including atomic force microscopy and polarization-resolved spectroscopy. We discuss the drawbacks of the typical approaches for nanostructure symmetry detection and propose a way to determine quantum dot geometrical aspect ratio based on high-resolution X-ray diffraction. The offered method provides a non-destructive insight into crystal lattice disturbances reflecting in-plane quantum dot geometrical aspect ratio.

Optimization of threshold characteristics of Hg0·8Cd0·2Te -based laser under interband breakdown in a lateral electric field

HgCdTe is promising as a material to solve a problem of development of semiconductor sources in mid- and far-infrared range due to small direct band gap. Since the compound materials HgTe and CdTe are closely lattice matched, it is possible to design a wide variety of multilayer structures based on HgCdTe. In this paper we calculate and optimize the parameters of the Hg0·8Cd0·2Te/Cd0·7Hg0·3Te separate-confinement double heterostructure which are required for lasing. It is shown that lasing at a wavelength of 10 μm for the optimal active region thickness (∼90 nm) and resonator length (∼2 mm) occurs when a lateral electric field of more than 0.96 kV/cm is applied at a temperature of 77 K. This corresponds to a small voltage of ∼10 V at a distance between metal contacts of 100 μm and the threshold current of ∼30 A.

Large-Scale Terahertz Sensor Array Module With Antenna-Coupled Microbolometers on Glass Substrate With Sigma–Delta ADC Readout ASIC

We describe the design, fabrication and demonstration of a terahertz sensor array module, designed to operate over 250-350GHz. The antenna coupled microbolometer was fabricated on a glass substrate with an integrated array of pixel switches and row multiplexing circuitry implemented with LTPS (Low Temperature PolySilicon) thin film transistors. While other microbolometer arrays have been reported for the upper Terahertz bands, we focus on lower frequencies where adequate semiconductor sources are available potentially enabling important medical and security applications. The devices were fabricated in a Gen 3.5 flat panel manufacturing facility implementing what we call Large Area MEMS Platform (LAMP) surface micromachining process, providing a path to low-cost manufacturing. Individual pixels were defined on a 0.7mm pitch across an array of 128x128 pixels in this first demonstration. Since flat panel fabrication capabilities use large, single-shot reticle masks and large glass substrates, physically larger arrays can be manufactured without mask stitching. An ROIC (readout integrated circuit) was demonstrated to support the THz sensor panel with 648 input channels, each providing an independent sigma delta ADC with excellent uniformity and 12 effective number of bits. An early demonstration of the sensor array is described, imaging a metallic knife hidden in a cardboard envelope.

On-chip generation of hybrid polarization-frequency entangled biphoton states

We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement, allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation. Our AlGaAs device is based on type-II spontaneous parametric downconversion in a counterpropagating phase-matching scheme in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization–frequency entangled photons at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong–Ou–Mandel interference (raw visibility 70.1 % ± 1.1 % ) of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization–frequency space.

Assessing neurotoxicity risk through electroretinography with reduced light irritation intensity

The article is devoted to questions of the risk assessment of human neurotoxicity caused by the negative influence of free radicals of nanostructures, using electrophysiological methods of research – electroretinography with low intensity of light irritation. It has been established that the negative influence of toxins (chemical compounds of industrial and household purposes, nanomaterials as a source of free radicals) leads to changes in the parameters of electroretinosignal (ERS) in the early stages of detection of neurotoxicity. The use of advanced electroretinography (by decreasing the intensity of light irritation) and the use of a low intensity stimulation semiconductor source is substantiated. The ERS was obtained in the required range of values of light irritation, and morphological parameters were determined for further detection of ERS in admixture with noise, and for evaluating the characteristic change of the form of ERS under the influence of neurotoxicity.

Thin active region HgCdTe-based quantum cascade laser with quasi-relativistic dispersion law.

HgCdTe is promising as a material to solve a problem of the development of semiconductor sources with an operational frequency range of 6-10 THz due to the small optical phonon energies and electron effective mass. In this study, we calculate the dependence of the metal-metal waveguide characteristics on the number of cascades for the 3-well design HgCdTe-based quantum cascade laser at 8.3 THz. It is shown that four cascades are sufficient for lasing at a lattice temperature of 80 K due to the large gain in the active medium. The results of this study provide a way to simplify the fabrication of thin active region HgCdTe-based quantum cascade lasers for operation in the range of the GaAs phonon Reststrahlen band inaccessible to existing quantum cascade lasers.

Design of a Controller Algorithm for Cascaded H- Bridge Multilevel Inverter System for Reduced THD and Improved Performance

Abstract: Multi-level inverter have huge advantages than the conventional inverter. This paper proposes 17 level cascaded multilevel inverter with minimum number of semiconductor switches and DC sources. A new controller is designed to trigger the switches of semiconductor devices to obtained the required output. To control the switching sequence of the metal oxide semiconductor field effect transistor(MOSFET) an embedded code is developed. 3- level, 5 -level ,17 -level and 27 -level cascaded H Bridge multi-level inverters are modelled on MATLAB/SIMULINK and Total Harmonic distortion (THD) of each level are compared to show the improved performance. Keywords: H-bridge, multilevel inverter, symmetrical DC-sources, asymmetrical H bridge topology

Direct Modulation and Free-Space Transmissions of up to 6 Gbps Multilevel Signals With a 4.65-$\mu$m Quantum Cascade Laser at Room Temperature

A roadmap for future wireless communications is expected to exploit all transmission-suitable spectrum bands, from the microwave to the optical frequencies, to support orders of magnitude faster data transfer with much lower latency than the deployed solutions nowadays. The currently under-exploited mid-infrared (mid-IR) spectrum is an essential building block for such an envisioned all-spectra wireless communication paradigm. Free-space optical (FSO) communications in the mid-IR region have recently attracted great interest due to their intrinsic merits of low propagation loss and high tolerance of atmospheric perturbations. Future development of viable mid-IR FSO transceivers requires a semiconductor source to fulfill the high bandwidth, low energy consumption, and small footprint requirements. In this context, quantum cascade laser (QCL) appears as a promisingtechnological choice. In this work, we present an experimental demonstration of a mid-IR FSO link enabled by a 4.65-μm directly modulated (DM) QCL operating at room temperature. We achieve a transmission data rate of up to 6 Gbps over a 0.5-m link distance. This achievement is enabled by system-level characterization and optimization of transmitter and receiver power level and frequency response and assisted with advanced modulation and digital signal processing (DSP) techniques. This work pushes the QCL-based FSO technology one step closer to practical terrestrial applications, such as the fixed wireless access and the wireless mobile backhaul. Such a QCL-based solution offers a promising way towards the futuristic all-spectra wireless communication paradigm by potentially supporting the whole spectrum from the MIR to the terahertz (THz).

Tailoring solid-state single-photon sources with stimulated emissions.

The coherent interaction of electromagnetic fields with solid-state two-level systems can yield deterministic quantum light sources for photonic quantum technologies. To date, the performance of semiconductor single-photon sources based on three-level systems is limited mainly due to a lack of high photon indistinguishability. Here we tailor the cavity-enhanced spontaneous emission from a ladder-type three-level system in a single epitaxial quantum dot through stimulated emission. After populating the biexciton (XX) of the quantum dot through two-photon resonant excitation, we use another laser pulse to selectively depopulate the XX state into an exciton (X) state with a predefined polarization. The stimulated XX-X emission modifies the X decay dynamics and improves the characteristics of a polarized single-photon source, such as a source brightness of 0.030(2), a single-photon purity of 0.998(1) and an indistinguishability of 0.926(4). Our method can be readily applied to existing quantum dot single-photon sources and expands the capabilities of three-level systems for advanced quantum photonic functionalities.

Broadly tunable lens-coupled nonlinear quantum cascade lasers in the sub-THz to THz frequency range

Room-temperature terahertz (THz) quantum cascade laser sources with intracavity difference-frequency nonlinear mixing are electrically pumped monolithic semiconductor laser sources operating in the 0.6–6 THz spectral range. We report widely tunable, low-frequency THz quantum cascade laser sources using a lens-coupled Cherenkov waveguide scheme. Based on a watt-class high-power, λ ∼ 13.7 μm quantum cascade laser, the monolithic THz source is strongly coupled with a high-resistivity silicon lens, which causes a major increase in the THz coupling efficiency and demonstrates significant performance improvements. A room-temperature 1.5 THz device produces a 0.2 mW peak output power with a high-quality beam pattern. Improved THz outcoupling efficiency using the lens-coupled scheme enabled the demonstration of a high-performance external-cavity semiconductor THz source that is tunable from 420 GHz to 2 THz. The external-cavity, lens-coupled device configuration can technically be assembled into a butterfly-style package for a thumb-sized, widely frequency tunable THz semiconductor source.

Electrical Properties of Compositional Al<sub>2</sub>O<sub>3</sub> Supplemented HfO<sub>2</sub> Thin Films by Atomic Layer Deposition

With advanced research for dielectrics including capacitors in DRAMs, decoupling filters in microcircuits and insulating gates in transistors, a lot of demand for the new challenging of high-k materials in semiconductor industries has been emerged. This study explores and addresses the experimental approach for composite materials with one of the major concerns of high capacitance, and low leakage, as well as ease of integration technology. The characteristics of Al2O3 supported HfO2 (AHO) thin films for a series of different Hf ratios with Al2O3 dielectrics by atomic layer deposition demonstrated as a candidate material. A composite AHO films with the homogeneous compositions of Al and Hf atoms into the Al-Hf-O mixed oxide system could stabilize the polycrystalline structure with increasing of dielectric constant (k) and decreasing of leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. 70 nm thick AHO thin films with different composition of Al and Hf contents were prepared by atomic layer deposition technique on titanium nitride (TiN) and silicon dioxide (SiO2) coated Si substrates. Photolithography and metal lift-off technique were used for the device fabrication of the metal-insulator-metal (MIM) capacitor structures. AHO films on TiN/SiO2/Si were measured by semiconductor analyzer and source/ measure system with probe station in the voltage range from -5 to 5 V with a frequency range from 10 kHz to 1 MHz were used to conduct capacitance-voltage (C-V) measurements with low/medium frequency range and current-voltage (I-V) measurements. It was found that Au/AHO/TiN/SiO2/Si MIM capacitors demonstrate a capacitance density of 1.5 - 4.5 fF/μm2 at 10 kHz, a loss tangent of 0.02 - 0.04 at 10 kHz, dielectric constant of 11.7 - 35.5 depending on the composition and a low leakage current of 1.7 × 10-9 A/cm2 at 0.5 MV/cm at room temperature. The acquired experimental results could show the possibility of compositional alloy thin films that could potentially replace or open new market for high-k challenges in semiconductor technology.

Improving the quality of active millimeter wave standoff imaging by incorporating the cross-polarized scattering wave.

In this paper, we study the feasibility of incorporating the cross-polarized scattered wave in active standoff millimeter-wave imaging in order to improve the edge detection and background suppression for metallic objects. By analyzing the scattering from a perfectly conducting (PEC) patch of a simple geometrical shape we show that the edge diffraction is the major source of cross-polarized scattering. A similar scattering behavior is also observed for a PEC patch placed on a dielectric medium. Hence, the cross-polarized scattered field conveys valuable information about the edges of the object. In addition, the cross-polarized scattering can be utilized to resolve the object from an unstructured reflective background. To put these ideas to the test, a standoff imaging system composed of a continuous-wave (CW) semiconductor source, a focal plane array detector (camera), and collimating and objective lenses at 95 GHz is utilized to image the co- and cross-polarized reflection from metallic patches both in the presence and in the absence of a background medium. In agreement with theory, the experiments reveal that the edges of the object can be enhanced and reflections from a smooth background medium can be suppressed by using the cross-polarized scattering. In this regard, the conducted experiments on the metallic patches placed on the human body also yield promising results.

A New Multilevel Inverter Topology with Reduced DC Sources

The component count for the multilevel inverter has been a research topic for the last few decades. The higher number of power semiconductor devices and sources leads to a higher power loss with the complex control requirement. A new multilevel inverter topology employing the concept of half-Bridge modules is suggested in this paper. It requires a lower number of dc sources and power components. The inverter is controlled using a fundamental frequency switching scheme. With the basic unit being able to produce 13 level voltage waveforms with three dc voltage sources, higher-level inverter configuration has also been discussed in the paper. The performance of the topology is analyzed in the aspects of circuit parameters and found better when compared to similar topologies proposed in recent literature. The comparison provided in the paper set the benchmark of the proposed topology in terms of lower component requirements. The topology is also optimized with two voltage fixing algorithms for maximizing the number of levels for the given number of IGBTs, drivers and dc sources, and the observations are presented. The efficiency analysis gives the peak efficiency as 98.5%. The simulations were carried out using the PLECS software tool and validated using a prototype rated at 500 W. The results with several test conditions have been reported and discussed in the paper.

Flexible entanglement-distribution network with an AlGaAs chip for secure communications

Quantum communication networks enable applications ranging from highly secure communication to clock synchronization and distributed quantum computing. Miniaturized, flexible, and cost-efficient resources will be key elements for ensuring the scalability of such networks as they progress towards large-scale deployed infrastructures. Here, we bring these elements together by combining an on-chip, telecom-wavelength, broadband entangled photon source with industry-grade flexible-grid wavelength division multiplexing techniques, to demonstrate reconfigurable entanglement distribution between up to 8 users in a resource-optimized quantum network topology. As a benchmark application we use quantum key distribution, and show low error and high secret key generation rates across several frequency channels, over both symmetric and asymmetric metropolitan-distance optical fibered links and including finite-size effects. By adapting the bandwidth allocation to specific network constraints, we also illustrate the flexible networking capability of our configuration. Together with the potential of our semiconductor source for distributing secret keys over a 60 nm bandwidth with commercial multiplexing technology, these results offer a promising route to the deployment of scalable quantum network architectures.

Zn(II)-tetracarboxy-phthalocyanine-Sensitized TiO2 Thin Films as Antimicrobial Agents under Visible Irradiation: a Combined DFT and Experimental Study.

In this article, we studied the antimicrobial activity of TiO2 sensitized by the Zn(II)-tetracarboxy-phthalocyanine (TcPcZn) complex using TiO2-Degussa P25 as a semiconductor source. The TiO2 thin films were deposited by the doctor blade method and were sensitized by the chemisorption process. The obtained compounds were characterized using Fourier transform infrared spectroscopy, UV–vis spectrophotometry, Raman spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy. Furthermore, we studied the stability of the adsorbed sensitizer on the semiconductor surface by using the density functional theory (DFT). Additionally, we determined the antimicrobial activity of TcPcZn–TiO2 against methicillin-resistant Staphylococcus aureus (MRSA). The Raman and optical results confirmed the sensitizing process. The TcPcZn–TiO2 thin films showed radiation absorption in the visible range of the electromagnetic spectrum (600–750 nm), and the dye anchored on the TiO2 surface had a band gap of 1.58 eV. The DFT study showed that TcPcZn supported on any phase of Degussa P25 is stable, making them suitable to act as catalysts in the proposed reactions. Finally, the TcPcZn–TiO2 thin films reached 76.5% of inhibition activity against MRSA.

New isostructural halide double perovskites Cs2GeNiX6 (X= Cl, Br) for semiconductor spintronics and thermoelectric advancements

The depletion of fossil fuels and tremendous increase in environmental pollution in the current era has turned the attention of the world's scientists to explore renewable alternative energy resources. Within the first principle calculations, from the Density Functional Theory (DFT) a compact overview on various physical properties of halide perovskites Cs2GeNiX6 (X ​= ​Cl, Br) has been summed up. The obtained values of relaxed lattice constants from the well-known Birch-Murnaghan equation and bond lengths are identical with previously reported values. The calibration of sophisticated Hubbard potential (GGA ​+ ​U) claims Cs2GeNiX6 (X ​= ​Cl, Br) have semiconducting nature with a total magnetic moment of 2 ​μB. Elastically and mechanically alloys are characterized to be stable via checked from their respective cubic elastic packages which display brittle/ductile strength. The flexibility of these perovskite structures suppresses the lattice thermal conductivity, which promotes an exclusive thermoelectric response. The occurrence of such properties in these layered structures lends their broad range of applications in semiconductor spintronics and power technology sources.