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We propose to explore tandem junctions associating single crystalline silicon bottom cell (Eg = 1.12 eV) and wide bandgap (1.7 eV) CuIn0.75Ga0.25S2 (pure-sulfide CIGSu) top cell, using GaP intermediate layer. Our purpose is to grow CIGSu films under epitaxial conditions on GaP/Si(001) to improve the top cell efficiency, thanks to a reduction of the structural defects density detrimental for the cell performance, so that CIGSu/Si tandem cells can emerge as cost competitive for the next generation of PV modules. Record efficiency on standard AZO/ZnMgO/CdS/CIGSu/Mo/Glass solar cell and epitaxy of CIGSsu on GaP/Si are demonstrated.

Terahertz quantum cascade lasers (THz QCLs) in metal-metal (MM) ridge waveguides have been fabricated and hetero bonded on aluminum nitride (AlN) substrate as heat sink submount. Compared with the conventional structure of THz QCLs in MM waveguides on gallium arsenide (GaAs) as receptor substrate, AlN performs superior heat dissipation properties for thermal management due to its much higher thermal conductivity. The light–current density–voltage (L-J-V) characterization shows comparable maximum operating temperature (Tmax) at 93-95 K for both THz QCLs bonded on AlN and GaAs under short pulse injection (250 ns). However, as the injected pulse duration increases for THz QCLs on GaAs, the light intensity drops quickly, eventually leading to lasing quenching when the pulse duration is above 30 µs at 80 K (heat sink temperature). On the other hand, THz QCL on AlN shows much stronger light intensity and slower decrease with the increase of the pulse duration; for example, the light intensity is 100 times higher for the THz QCL on AlN (pulse duration of 40 µs) than THz QCL on GaAs (pulse duration of 30 µs) at the same measurement conditions at 80 K. This study shows suspected joule heating plays a great role on THz QCLs operating from long duty cycle towards continuous-wave (CW) mode, indicating AlN substrate as a high thermal conductivity material produces superior thermal management for heat extraction and dissipation.

A rising photonic platform, aluminum gallium arsenide on insulator (AlGaAsOI), has led to remarkable breakthroughs in integrated photonics over last few years. In this talk, we will introduce the key progress on this platform, including development of low loss AlGaAsOI waveguide, many record-breaking efficient nonlinear processes enabled by ultra-high Q resonators, as well as the recent demonstration of the brightest entangled photon pair generation on chip. We will discuss the potential AlGaAsOI holds for realizing high performance quantum photonics devices and fully integrated photonic quantum circuits in the future.

The purpose of this study was to evaluate the performance of mammography images acquired with a prototype Gallium Arsenide (GaAs) photon counting detector. The contrast to noise ratio was measured using different aluminum/PMMA phantoms of different thicknesses. In addition, microcalcification detection accuracy was evaluated using a receiver operating characteristic (ROC) study with three observers reading an ensemble of images for each case. For both studies, comparisons were made to a commercial mammography system. The contrast to noise ratio was estimated by imaging 18, 36 and 110 μm thick aluminum targets placed on top of 6 cm of PMMA plates and was found to be similar or better over a range of exposures. Similar task performance in detecting microcalcifactions was observed between the systems over a range of clinically applicable dose levels with a small increase in GaAs’s system at lower dose levels. The GaAs system was evaluated using a typical mammography X-ray spectrum provided by the Automatic Exposure Settings (AEC) of the commercial mammography system and using only one energy threshold (i.e, one energy window). Operating the GaAs detector with multiple energy windows (i.e., two energy windows) may provide improved performance for a given dose.

The paper uses secondary research to investigate various constructs and functional structures of GaN as a thirdgeneration semiconductor. A brief history of semiconductors is provided in terms of the generations that they occur. GaN was introduced in the 1990s, but its utility evolved until the 21st century. At the advent of its invention, Silicon (Si) and germanium (Ge) had been the most commonly used semiconductors. GaN presented unique advantages ranging from cost to size and utility. This was the frontier of new applications of semiconductors. The largest applications of GaN have been in LEDs, transducers, and transistors. GaN also has its limitations, which include its generally immobile energy band, and its substrate incompatibility. The future of GaN can be projected by factoring three main variables. These are cost, application/utility, and limitations.

Around 1970, the operation of semiconductor lasers that emit continuous light at room temperature was performed at Bell Labs by Izuo Hayashi and Morton B. Panish {1970 HAY}, independent of the results in the Soviet Union achieved by Zh. I. Alferov and coworkers {1969 ALF}. This was achieved by a method of forming gallium arsenide (GaAs) and gallium aluminum arsenide (GaAlAs), to which aluminum was added by crystal growth. In the fall of that year, Dr. Hayashi visited the Tokyo Institute of Technology by the invitation of Prof. Suematsu and gave a talk on the experimental results. The crystal growth of the “double heterostructure,” which is a sandwich structure of GaAlAs/GaAs /GaAlAs, performed by coinvestigator Panish was excellent. The heterostructure was patented by Herb Kromer in 1962 {1963 KROa, 1963 KROb}, and he was awarded the 2000 Nobel Prize in Physics for it. Most researchers were not aware of this patent. The demonstration by Hayashi and Panish showed the effectiveness of the double heterostructure, which revealed Kromer’s idea to the world.

Sb-based III-V semiconductors are a promising alternative to HgCdTe. They can be produced with a similar bandgap to HgCdTe, but take advantage of the strong bonding between group III and group V elements which leads to very stable materials, good radiation hardness, and high uniformity. In this paper, we will discuss the recent progress of our research and present the main contributions of the Center for Quantum Devices to the Sb-based 3th generation imagers.

Nonlinear optics is present in our daily life with many applications, e.g. light sources for microsurgery or green laser pointer. All of them use bulk materials such as glass fibres or crystals. Generating nonlinear effects from materials at the nanoscale can expand the applications to biology as imaging markers or sensors, and to optoelectronic integrated devices. However, the nonlinear emission efficiency of nanostructures is low due to their small volumes. In our work, we show strategies to enhance the second harmonic generation (SHG) at the nanoscale with the goal of developing nonlinear photonics devices for a broad spectral range. So far, the SHG from metallic and semiconductor nanostructures as gold or gallium arsenide has been successfully shown. However, the application range of these materials is generally limited to the visible-near-infrared range by their high absorption. We use metal oxides such as barium titanate (BTO) and lithium niobate (LNO) as an alternative platform for nanoscale nonlinear photonics in a broad spectral range. Both BTO and LNO are noncentrosymmetric materials with high refractive index and high energy band gaps, transparent down to the near-ultraviolet range. We demonstrate linear Mie resonances in BTO and LNO nanostructures, such as nanospheres or nanocubes. Further, we show that these resonances enhance the SHG emission from the nanostructures. We also perform simulations to understand the underlying mechanism of this enhancement. Finally, we explore fabrication methods for BTO and LNO nanostructures that will allow the controlled integration of BTO and LNO nanostructures for nonlinear metasurfaces.

Emerging applications in sensing, LIDAR, spectroscopy, and SWIR imaging require photodetectors operating at wavelengths beyond the range of silicon technology and that can be produced cost-effectively for very high-volume consumer and commercial markets. In this paper, Array Photonics, Inc. introduces a new generation of photodetectors designed to meet these requirements. We provide an update on PIN photodetectors and detector arrays based on our dilute nitride material (GaInNAsSb) grown epitaxially on and lattice matched to gallium arsenide (GaAs) substrates. We present our latest photodetector results demonstrating broadband operation from 450 nm to 1450 nm with peak responsivity of over 0.85 A/W at 1300 nm and dark current density of 3×10-5 A/cm2 at -1V bias voltage. These dilute nitride-on-GaAs photodetectors are now commercially available as single elements, 1-D arrays and small 2-D arrays and are referred to as eGaAs™ (extended GaAs) photodetectors. We also briefly discuss ongoing work to migrate from 4” (100 mm) to 6” (150 mm) GaAs wafers and the implementation of larger size 2-D arrays for imaging applications in the automotive and industrial markets.

Reduction of unwanted light reflection from a surface of a substance is very essential for the improvement of the performance of optical and photonic devices. Anti-reflection (AR) surface textures can be created on the surface of lenses and other optical elements to reduce the intensity of surface reflections. AR textures are indispensable in numerous applications, both low and high power, and are increasingly demanded on highly curved optical components. Nanofabrication involves the fabrication of devices at the nanometer scale. In this work, we used nanofabrication to design and fabricate nanostructures of squares and hexagons of different spatial pitch and gap width in Gallium Arsenide (GaAs). These structures have a gap of 300nm, 400nm, and pitch of 900nm, 1000nm and 1100nm. The fabrication process involves solvent cleaning, deposition of silicon oxide, soft and hard bake, photolithography and development. Both wet and dry etching were used to fabricate the expected structures. Results from scanning electron microscopy (SEM) to examine the shapes of the fabricated arrays are presented in this study. By combining dry and wet etches, we obtained the desired shapes and depth of hexagons and squares with rounded edges. We report detailed fabrication processes and their corresponding results at each step.

Travelling-wave electro-optic modulators designed for V-band space applications using gallium arsenide guided-wave technology are presented. The designs feature a low-loss folded optical configuration giving straight-line RF access at one end of the chip, with all optical I/O via the opposite end. This configuration enables the close-packed monolithic modulator arrays needed for phased-array applications, contributes to high modulation bandwidths with low ripple by eliminating directional change in the RF feed arrangements and facilitates compact packaging. While only 1550nm designs are reported here, the AlGaAs material system is versatile, permitting modulators to be realized for a wide range of optical wavelengths, with particular advantage in drive-power at shorter wavelengths. Both single MZ and monolithic dualparallel (IQ) modulators have been assessed up to 70GHz; bandwidths around 50GHz are achieved with low-frequency Vπ of 4.6V. Typically, the folded devices are half the length of conventional format modulators and can accommodate 4 device arrays in the same width package.

Since the very first demonstration of a vertical-cavity surface-emitting laser (VCSEL) incorporating subwavelength high refractive index contrast grating (HCG) membrane mirror in 2007 by the group of Prof. Chang-Hasnain, numerous research groups around the world have presented devices based on the same concept emitting at wavelengths from ~400 to 1550 nm manufactured in gallium nitride (GaN), gallium arsenide (GaAs) and indium phosphide (InP) material systems. On one hand, an open access to a VCSEL cavity through an air gap combined with a very low inertia of an HCG mirror opened a way for a large range of emission wavelengths in MEMS tunable VCSELs. On the other hand, an air gap in a cavity generally hinders heat and current flow, while the potentially rather fragile HCG membrane is prone to mechanical instability. We present electrically-injected VCSELs incorporating monolithic HCG (MHCG) mirrors. An MHCG mirror being a special case of an HCG mirror, keeps the extraordinary features of an HCG such as scalability with wavelength, ultra-low thickness and very large power reflectance, but doesn't have to be surrounded by a low refractive index material and hence can be monolithically integrated with an all-semiconductor VCSEL cavity. We present an extensive analysis of the impact of the MHCG parameters on the modal properties and thermal stability of single- and double-mode devices, with various oxide apertures. We additionally compare MHCG VCSELs and generic distributed Bragg reflector VCSELs in terms of modal properties and temperature stability based on measured data and the results of computer simulations.

Integrated quantum photonic circuits are promising for an on-chip realization of a quantum advantage. It is desirable to develop a platform which allows dense integration of functionalities, which includes sources, photon processing units and detectors on the single photon level. Among the different material platforms currently being investigated, direct-bandgap semiconductors and particularly gallium arsenide offer the widest range of functionalities, including single and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation, and single-photon detection. We summarize the potential and current status in the field of quantum integrated photonic components and circuits based on the GaAs technology platform.

Laser cooling of gallium arsenide is of high industrial and academic interest and has been actively investigated using different experimental methods based on steady-state concepts. We demonstrate for the first time an onset of transient cooling in GaAs after an impulsive excitation, verified by two independent methods of time-resolved spectroscopy. We observe that transient cooling lasts for about 100 ps, becoming overwhelmed on longer timescales by parasitic heating associated with the nonlocal character of the background absorption processes. In addition, new insights into the physics of the Urbach tail excitation, being at the heart of the laser cooling in semiconductors, are revealed.

Orientation-patterned gallium arsenide (OP-GaAs) and gallium phosphide (OP-GaP) have enabled exciting advances in frequency-combs for spectroscopy in the molecular fingerprint region beyond the transparency limits of quasi-phase matched (QPM) oxides like PPLN and PPKTP. These QPM semiconductors also offer much higher nonlinearities for pumping at 1-m (OP-GaP, d14 ~ 70 pm/V), 1.5m (OP-GaP, d14 ~ 35 pm/V), or 2m (OP-GaAs, d14 = 94 pm/V). In ferroelectric oxides like PPLN, the periodic QPM structure is created by the use of electric-field poling through a photo-lithographically defined insulator to reverse the polarity (and hence the sign of the nonlinear coefficient) of alternating domains. Nonlinear optical semiconductors like GaAs and GaP are not ferroelectric, however, so the QPM grating structure must is created instead by polar-on-nonpolar MBE whereby an inverted GaAs (GaP) epi-layer (grown on a on a thin, lattice-matched non-polar Ge (Si) layer) photolithographically patterned, etched, and regrown to produce thick QPM layers (t ~ 1mm) for in-plane laser pumping. A primary advantage of QPM is that the frequency conversion process can be engineered in various ways through the design and layout of the grating structure to achieve discrete and continuous wavelength tuning by translation across multiple adjacent gratings or fan gratings respectively. Tandem grating periods enable sequential processes such as photon recycling for enhanced efficiency, and chirped grating structures allow spectral tailoring of the frequency conversion process. While previously achieved in ferroelectric oxides, here we demonstrate the same novel structures in QPM semiconductors and discuss the implications for device design.

We demonstrate optical and electrical property enhancement of solar cells using a variety of dielectric nano-resonator array coatings. First, we study close-packed silicon dioxide (SiO2) nano-resonator arrays on top of silicon (Si) and gallium arsenide (GaAs) solar cells. From macroscale measurements and calculations, we find that absorptivity of solar cells can be improved by 20 % due to the resonant couplings of excited whispering gallery modes and the thin-film antireflection effect. Next, we image photocurrent enhancement at the nanoscale via near-field scanning photocurrent microscopy (NSPM). Strong local photocurrent enhancement is observed over each nano-resonator at wavelengths corresponding to the whispering gallery mode excitation. Finally, for better optical coupling to solar cells, we explore hybrid nano-resonator arrays combining multiple materials such as silicon dioxide, silicon nitride, and titanium dioxide. Due to higher number of photonic modes within such hybrid coatings, absorptivity is enhanced by more than 30 % in a Si solar cell.

This article studies stability control of laser wireless energy transfer, and experiment is presented. Based on transfer optical experiment, the experiment of broadband gallium arsenide (GaAs) cells and monocrystalline silicon (Si) cells photoelectric conversion ratio was tested. We comprehensively studied the factors that affect the conversion efficiency of photovoltaic cells. Different wave band, incident power, uniformity of power density, incident angle, and temperature were listed as main factors in our experiment. And uniformity of power density and temperature are found to be important for the efficiency of photocell conversion. With the relatively uniform power density at 808 nm, the highest photoelectric conversion ratio for GaAs photocell and Si photocell was measured to be 55% and 25% respectively, Besides, photoelectric conversion ratio was insensitive to angle that range ±10°. This work may provide experimental data accumulation to improve the conversion efficiency for long-distance wireless laser energy transmission and even solar power station in the near future.

Resonant high-index dielectric nanostructures have recently emerged as a new direction in nanophotonics, which might compliment and/or substitute conventional plasmonics in multiple application areas [1]. Major advantages of dielectric nanoantenna approach are low losses at optical frequencies and wide range of appropriate materials such silicon, germanium, gallium arsenide, titanium dioxide, and other semiconductors, which are well known and widely accepted by existing semiconductor industries. Apart from that, high-index dielectric nanostructures naturally possess strong optical magnetic and electric resonances, which open opportunities to observe novel effects related to optical magnetism as well as to interference of coherent electric and magnetic responses. Some of such new effects related to directional light scattering (also known as Kerker conditions), Huygens’ dielectric metasurfaces and generalized Brewster effect have already been demonstrated over the last few years [1]. In this talk, I will focus on application of resonant effects in dielectric nanoantennas and metasurfaces to design devices with unique functionalities. In particular I will show how resonance interference in dielectric metasurfaces can be applied to efficiently bend visible light at extremely high angles (>80 degrees). Based on this effect I will demonstrate flat lenses with free-space numerical aperture of ~0.99, which significantly exceed all flat and bulk optics analogues. I will also show how metasurfaces can be designed to operate simultaneously at all RGB wavelengths in the visible spectrum. References: 1) A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016). 2) R. Paniagua-Dominguez et al., “A metalens with near-unity numerical aperture”, arXiv:1705.00895 (2017). 3) E. Khaidarov et al., “Asymmetric nanoantennas for ultra-high angle broadband visible light bending”. Nano Letters (2017), DOI: 10.1021/acs.nanolett.7b02952.

In this work, we demonstrate two times enhancement in NEDT response of InAs/InGaAs/ GaAs dot-in-the-well (DWELL) structure implanted with hydrogen ions of 3 MeV energy and 5×1012 ions/cm2 fluence. Low temperature photoluminescence study shows emission peak at 1130 nm which corresponds to ground state transition between conduction to valence band. PL enhancement is observed in all hydrogen implanted samples indicating the passivation of defects/dislocations in the vicinity of QDs and surrounding layer. The spectral response peak was observed at 5 μm corresponding to the intersubband transition and measured upto 76 K. Next, 320×256 format infrared FPA was fabricated involving multistage lithography, wet etching, metal stack and bump deposition. The NEDT parameter, which represents minimum temperature difference that FPA based camera can resolve, improved from 239 mK( as-grown) to 129 mK ( implanted sample).

Through the European Defence Agency, the Joint Investment Programme on CBRN protection funded the project AMURFOCAL to address detection at stand-off distances with amplified quantum cascade laser technology in the longwave infrared spectral range, where chemical agents have specific absorptions features. An instrument was developed based on infrared backscattering spectroscopy. We realized a pulsed laser system with a fast tunability from 8 to 10 μm using an external-cavity quantum cascade laser (EC-QCL) and optical parametric amplification (OPA). The EC-QCL is tunable from 8 to 10 μm and delivers output peak powers up to 500 mW. The peak power is amplified with high gain in an orientation-patterned gallium arsenide (OP-GaAs) nonlinear crystal. We developed a pulsed fiber laser acousto-optically tunable from 1880 to 1980 nm with output peak powers up to 7 kW as pump source to realize an efficient quasi-phase matched OPA without any mechanical or thermal action onto the nonlinear crystal. Mixing the EC-QCL and the pump beams within the OP-GaAs crystal and tuning the pump wavelength enables parametric amplification of the EC-QCL from 8 to 10 μm leading to up to 120 W peak power. The output is transmitted to a target at a distance of 10 – 20 m. A receiver based on a broadband infrared detector comprises a few detector elements. A 3D data cube is registered by wavelength tuning the laser emission while recording a synchronized signal received from the target. The presentation will describe the AMURFOCAL instrument, its functional units and its principles of operation.

II-VI chalcogenides (e.g. ZnSe/S) doped with transition metal (TM) ions such as Cr, and Fe are arguably the materials of choice for fabrication of effective mid-IR gain media. TM:II-VI materials feature a favorable blend of laser spectroscopic parameters: a four-level energy structure, absence of excited state absorption, close to 100% quantum efficiency of fluorescence (for Cr doped II-VI media), broad mid-IR vibronic absorption and emission bands. This talk summarizes progress in fabrication of high quality Cr:ZnS/Se and Fe:ZnS/Se by cation vacancy and cation interstitial enhanced post growth thermal diffusion. We also describe recent breakthrough on recrystallization and effective doping of ZnS ceramics under hot isostatic pressing resulting in a large cm-scale monocrystalline domains formation and an increase of the Fe diffusion coefficient by three orders of magnitude. We report recent advances in high-power Cr:ZnS/Se and Fe:ZnSe laser systems, enabling a wide range of tunability (1.8-5.0µm) with output power levels of up to 140 W near 2500 nm, 32 W at 2940 nm, and 35 W at 4300 nm with corresponding optical efficiencies of 62%, 29%, and 35%. Current improvements of output characteristics of polycrystalline Cr:ZnS/Se oscillators in Kerr-Lens-Mode-Locked (KLM) regime are reported: up to 2 W output power at 75-1200 MHz repetition rate, up to 2 cycle pulse duration (16 fs) with efficiency of 20-25% with regards to Er-fiber laser pump power. The effects of efficient up-conversion of mid-IR fs pulses in the laser medium as well as supercontinuum generation are demonstrated. Further extension of mid-IR spectral coverage to 3-8 m is demonstrated by Cr:ZnS KLM laser pumped degenerate (subharmonic) parametric oscillators (OPOs) based on based on quasi-phase matching in orientation-patterned gallium arsenide, and random phase matching in polycrystalline ZnSe.

High-average power, ultra-broadband, mid-IR radiation can be generated in a nonlinear medium by illuminating it with a multi-line laser radiation. Propagation of a multi-line CO 2 laser beam in a nonlinear medium, e.g. gallium arsenide or chalcogenide, will generate directed, broadband, IR radiation in the atmospheric window (2-13 μm). A 3-D laser code for propagation in a nonlinear medium has been developed to incorporate extreme spectral broadening resulting from the beating of several wavelengths. The code has the capability to treat coupled forward and backward propagating waves. In addition, we include transverse and full linear dispersion effects. Methods for enhancing the spectral broadening are proposed and analyzed; in particular, grading the refractive index radially will tend to guide the CO 2 radiation and extend the interaction distance, allowing for enhanced spectral broadening. Finally, we show that the laser phase noise associated with the finite CO 2 linewidths can significantly enhance the spectral broadening. In a dispersive medium laser phase noise results in laser intensity fluctuations. These intensity fluctuations result in spectral broadening due to the self-phase modulation mechanism.

The combination of nonlinear and integrated photonics enables applications in telecommunication, metrology, spectroscopy, and quantum information science. Pioneer works in silicon-on-insulator (SOI) has shown huge potentials of integrated nonlinear photonics. However, silicon suffers two-photon absorption (TPA) in the telecom wavelengths around 1550 nm, which hampers its practical applications. To get a superior nonlinear performance, an ideal integrated waveguide platform should combine a high material nonlinearity, low material absorption (linear and nonlinear), a strong light confinement, and a mature fabrication technology. Aluminum gallium arsenide (AlGaAs) was identified as a promising candidate for nonlinear applications since 1994. It offers a large transparency window, a high refractive index (n approximate to 3.3), a nonlinear index (n2) on the order of 10(-17) m(2)W(-1), and the ability to engineer the material bandgap to mitigate TPA. In spite of the high intrinsic nonlinearity, conventional deep-etched AlGaAs waveguides exhibit low effective nonlinearity due to the vertical low-index contrast. To take full advantage of the high intrinsic linear and nonlinear index of AlGaAs material, we reconstructed the conventional AlGaAs waveguide into a high index contrast layout that has been realized in the AlGaAs-on-insulator (AlGaAsOI) platform. We have demonstrated low loss waveguides with an ultra-high nonlinear coefficient and high Q microresonators in such a platform. Owing to the high confinement waveguide layout and state-of-the-art nanolithography techniques, the dispersion properties of the AlGaAsOI waveguide can be tailored efficiently and accurately by altering the waveguide shape or dimension, which enables various applications in signal processing and generation, which will be reviewed in this paper.

To improve the power handling ability of NonlinearTransmission Lines (NLTLs), multiple barrier varactordevices are utilized. NLTLs have been designed andfabricated on GaAs wafers with a variety of stackedmulti-barrier structures.

There is increasing interest in the use of optical methods for managing RF signals in space, with applications for both ground-to-satellite and inter-satellite communications readily envisaged. The potential weight-saving of optical fiber over metallic waveguide or coaxial channels is very significant; moreover, there are obvious advantages to be gained from the enormous data capacity of multiplexed fiber links.

We present a hybrid photonic architecture using gallium arsenide photonic crystals coupled to silicon nitride waveguides. Chrome microheaters are integrated in the system for tuning the cavities. The combination of low-energy switching elements, combined with low loss photonic waveguides provides an ideal architecture for applications in dedicated optical computing and machine learning applications.

In recent years, there has been interest in lanthanide monopnictide (Ln-V) nanoparticles (especially ErAs) embedded within III-V semiconductors for photoconductive switches and photomixers for terahertz generation and detection. Photoconductive switches based on ErAs:GaAs have proven quite effective, especially when compared to conventional materials such as low temperature-grown GaAs (LT-GaAs) or radiation-damaged silicon on sapphire. At the same time, the ability to pump a photoconductive switch with 1064nm or 1550nm fiber-coupled lasers rather than titanium-sapphire lasers represents a critical step to wider adoption of terahertz spectroscopy and related technologies. Accordingly, we report on the growth and characterization of ErAs nanoparticles epitaxially embedded within GaBiXAs1-X. The incorporation of bismuth into III-V semiconductors has been shown to reduce the bandgap, and here, we demonstrate that such ErAs:GaBiAs nanocomposite materials have the requisite electrical and optical properties (i.e. appropriate bandgap, high dark resistance, high mobility, and short carrier lifetime) to be promising materials for photoconductive switches and photomixers operating at 1064nm and longer optical wavelengths. We will also discuss approaches to further extend this wavelength. Additionally, we will discuss our recent work on TbAs-containing materials in which the trap states associated with the nanoparticles can be saturated, providing carrier lifetimes that depend strongly on optical fluence. We believe these materials might provide a path to new terahertz device technologies.

In0.53Ga0.47As/InP single photon avalanche detectors (SPADs) have a high photon detection efficiency in the near-IR, however the dark count rate is prohibitively high at room temperature. A nanowire-based In0.3Ga0.7As/GaAs SPAD can significantly reduce the DCR through a nearly three order of magnitude reduction in bulk InGaAs volume, as well as by reducing the indium composition for operation at 1064 nm. As a first step, we have successfully grown axial InGaAs/GaAs heterostructures using catalyst-free selective-area epitaxy. We will present the electrical characterization of a vertically oriented nanowire array InGaAs/GaAs SPADs operating at 1064 nm and use 3-dimensional modeling to aid in the analysis.

II-VI compounds are promising materials for the fabrication of room-temperature terahertz devices due to their beneficial properties like as type-I conduction band alignment, high breakdown field strength (~331 kV/cm for ZnSe vs. ~80 kV/cm for GaAs), and higher values of the conduction band offset (1.5 eV for BeSe/ZnSe vs. 0.7 eV for AlAs/GaAs). In this paper we report on numerical study of the resonant tunneling transport in ZnBeSe/ZnSe/ZnBeSe symmetric and asymmetric resonant tunneling diodes (RTDs). The negative differential resistance feature is observed in the current-voltage characteristics of the ZnSe-based RTDs. It is found that the maximum of peak-to-valley ratio (PVR) of the current density is equal to 6.025 and 7.144 at 150 K, and to 1.120 and 1.105 at 300 K for the symmetric and asymmetric RTDs, respectively. The effect of barrier heights on the frequency and output power performance of RTD devices are studied and discussed.

Successful integration of ultrathin flexible or stretchable systems with new applications, such as medical devices and biodegradable electronics, have intrigued many researchers and industries around the globe to seek materials and processes to create high-performance, non-invasive and cost-effective electronics to match those of state-of-the-art devices. Nevertheless, the crucial concept of transmitting data or power wirelessly for such unconventional devices has been difficult to realize due to limitations of radio-frequency (RF) electronics in individual components that form a wireless circuitry, such as antenna, transmission line, active devices, passive devices etc. To overcome such challenges, these components must be developed in a step-by-step manner, as each component faces a number of different challenges in ultrathin formats. Here, we report on materials and design considerations for fabricating flexible and stretchable electronics systems that operate in the microwave level. High-speed flexible active devices, including cost effective Si-based strained MOSFETs, GaAs-based HBTs and GaN-based HEMTs, performing at multi-gigahertz frequencies are presented. Furthermore, flexible or stretchable passive devices, including capacitors, inductors and transmission lines that are vital parts of a microwave circuitry are also demonstrated. We also present unique applications using the presented flexible or stretchable RF components, including wearable RF electronics and biodegradable RF electronics, which were impossible to achieve using conventional rigid, wafer-based technology. Further opportunities like implantable systems exist utilizing such ultrathin RF components, which are discussed in this report as well.

Investigated were the opportunities of direct conversion of modulated laser radiation with mean power of 10–40 dBm for combined power and information transfer fiber-optic lines. Have been studied optical sensors based on common p-n AlGaAs/GaAs and n-p GaInP/GaAs structures, including the ones with multiple photovoltaic cells, providing acceptable efficiency values at optical-to-electrical conversion at wavelength 809–830 nm. Developed was a special circuit allowing extraction of the information signal at one time with power conversion. Shown, that at 30–35 dBm of incident power, laser power converters can demonstrate up to 55 % efficiency and 500 MHz bandwidth. Maximum laser source modulation depth in these modes shouldn’t exceed 3.5 %.

Three types of laser irradiating experiments on single junction GaAs solar cells with the same laser energy coupling intensity were carried out, which were irradiated by in-band (808 nm) and out-of-band (1.07 μm) continuous wave lasers respectively and simultaneously. On the basis of the changes of current-voltage characteristic curves of irradiated solar cells, the damage degrees could be divided into three stages which were gently, seriously and thoroughly damaged stages. The damage mechanism was studied from two aspects: output changes of solar cell equivalent circuit under different configuration settings, thermal analysis model. The results show that damage degrees of gently and thoroughly damaged stages is insensitive to irradiation intensity. However, the damage degree of seriously damaged stage is sensitive to irradiation intensity and this is regarded to be related to thermal decomposition of GaAs. Moreover, the increase of PN junction defects leads to performance degradation of irradiated solar cells. In conclusion, the thermal damage leads to the increase of PN junction defects, thus results in the performance degradation of cells.

A real-time method based on laser scattering technology was used to detect the interaction process of GaAs with a 1080 nm laser. The detector collected the scattered laser beam from the GaAs wafer. The main scattering sources were back surface at first, later turn into front surface and vapor, so scattering signal contained much information of the interaction process. The surface morphologies of GaAs with different irradiation times were observed using an optical microscope to confirm occurrence of various phenomena. The proposed method is shown to be effective for the real-time detection of GaAs. By choosing a proper wavelength, the scattering technology can be promoted in detection of thicker GaAs wafer or other materials.

This paper reports progress on a type of ultrafast photoconductive source that can be driven at 1550 nm but exhibits the robustness of GaAs (e.g., low-temperature-grown GaAs) driven at 780 nm. The approach is GaAs doped heavily with Er (≈4x1020 cm-3 or 2% atomic-Er-to-Ga fraction) such that ErAs nanoparticles form spontaneously during epitaxial growth by MBE. The nanoparticles are mostly spherical with a diameter of a few nm while the packing density is estimated as high as ~2.2x1019/cm3. Yet, the Er-doped GaAs epilayer maintains excellent structural quality and smooth surface morphology. A photoconductive switch coupled to a 4-turn square spiral antenna is fabricated and characterized. At least ~40 μW average THz power is generated when the device is biased at 75 V and pumped with a 1550-nm 90-fs-short pulsed laser having average power ~85 mW. This research is significant for 1550-nm-technologycompatible, cost-effective THz sources.

In view that enhancing near-infrared response of photocathodes is critical to the detection performance, we propose two technical approaches by changing the structure of buffer-layer underneath the active-layer, wherein one is to produce a graded band gap using the graded-composition structure, and the other is to produce a distributed Bragg reflector using the AlAs/GaAs supperlattice structure. Three types of reflection-mode GaAs photocathode samples grown by molecular beam epitaxy were prepared under the same condition. By comparison of activation photocurrent and spectral response among the three different samples, it is found that compared with the conventional sample, the samples with graded-composition and distributed Bragg reflector can obtain higher photocurrent and better response. The measured results of spectral response indicate that the samples without a distributed Bragg reflector exhibit a typical smooth spectral behavior, while the spectral response of the sample with a distributed Bragg reflector structure has a different resonance feature. The sample with the distributed Bragg reflector structure can obtain higher response than those without distributed Bragg reflector at some near-infrared wavelength positions. The peak positions of spectral response curve agree quite well with the dip positions in the reflectivity spectrum. This agreement demonstrates that the response enhancements are ascribed to the resonant absorption effect.

The type-I to type-II band alignment transition in InAlAsAs/AlGaAs/GaAs self-assembled quantum dots (QDs) is investigated when the Al-composition in QDs and barrier are changed. In particular, the In0.46Al0.54As/Ga0.46Al0.54As/GaAs QDs show unique optical properties. The PL peak energy has a blue-shift of >40 meV when the laser intensity increases by four orders of magnitude, indicating a type-II band alignment of the QDs. The formation of the type-II band alignment is explained by that the quantum-confinement effect pulls up the minimum electron energy level in the QDs and the Γ→X transition in the Ga0.46Al0.54As barrier. The time-resolved PL (TRPL) spectrum of QDs at peak wavelength exhibits a double-component decay behavior, suggesting the possibility of type-I and type-II band alignment coexistence in this QD sample. The continuum state of the QDs is also investigated. Emission associated with the continuum states of the QDs is directly observed in PL spectra. The PL excitation (PLE) and TRPL spectra reveal an efficient carrier relaxation from the AlGaAs barrier into the InAlAs QD ground state via the continuum states. The carrier recombination in the continuum states can compete with that in the QDs due to the long recombination lifetime in the type-II QDs. This feature of continuum state emission can not be observed for normal InGaAs/GaAs QDs with the type-I band structure.

Despite years of research and development, integrated laser sources remain a bottleneck for silicon photonics (SiPh). Integration of lasers into SiPh can be categorized as hybrid, heterogeneous, or monolithic. Hybrid approaches are the most mature. One example is the co-packaging of lasers with micro-optics and subsequent coupling of laser light to silicon waveguides. More scalable hybrid approaches include butt coupling of lasers and silicon waveguides without the use of micro-optics. This could be accomplished with two chips mounted side by side on a common carrier or by flip-chip bonding of laser chips into recesses adjacent to silicon waveguides. Heterogeneous approaches involve the intimate merging of traditionally incompatible materials and subsequent co-fabrication of these materials to form devices. This approach allows for best-in-class materials selection, however, co-fabrication requires complex fabrication processes. The term monolithic ordinarily refers to a single substrate and materials compatible with the substrate material. Germanium on silicon could be considered a monolithic approach, as could growth of III-V materials (such as indium phosphide (InP) and gallium arsenide) on silicon. This paper summarizes a novel 3D hybrid integration approach that is scalable, low cost, reliable, and that demonstrates superior thermal performance. The approach is based on flip-chip bonding and vertical coupling between InP and silicon waveguides. For the InP waveguide, vertical emission is achieved with a total internal reflection turning mirror. For the silicon waveguide, vertical coupling is achieved with a grating coupler. The InP chip is flip-chip bonded directly to the silicon substrate providing an effective heat sink.

Orientation patterned GaAs and GaP crystals are increasingly being used for frequency conversion of laser beams into desired wavelengths. The ternary alloy InGaAs has smaller band gap energy compared to GaAs and is expected to have a nonlinear optical coefficient that is higher than that of GaAs. We will present the results of measurements of the second order nonlinear optical coefficient of InGaAs, along with recent measurements of GaAs and GaP obtained through second harmonic generation of a tunable carbon dioxide laser in the 9.2 to 10.6 μm range. The results will be compared to available values obtained at other wavelengths [1,2] Keywords: nonlinear optics, frequency conversion, second harmonic generation REFERENCES [1] T. Skauli, K. L. Vodopyanov, T. J. Pinguet, A. Schober, O. Levi, L. A. Eyres, M. M. Fejer, J. S. Harris, B. Gerard, L. Becouarn, and E. Lallier, G. Arisholm, “Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation”, Optics Letters , Vol. 27, No. 8, 628, (2002) [2] I. Shoji, T. Kondo, A. Kitamoto, M. Shirane, and R. Ito, “Absolute scale of second-order nonlinear-optical coefficients”, J. Opt. Soc. Am. B, Vol. 14, No. 9, 2268, 1997

Ga(AsBi) quantum well (QW) active regions are an alternate to dilute-nitride QWs for achieving lasers in the telecom wavelength regions (λ~1.3-1.55μm) on GaAs substrates. Ludewig et al first reported the successful operation of Ga(AsBi) single quantum well laser in 2013 [1] with low threshold current densities, Jth=1.56kA/cm2 where (AlGa)As was used as a barrier material for low Bi-content QWs to improve the electron confinement in the conduction band and reduce thermally activated carrier leakage from the QW. We implement here the use of tensile-strained Ga(AsP) as a QW barrier material, providing carrier confinement as well as potential for strain-balancing. Laser structures employing a single GaAs0.976Bi0.024 quantum well (SQW) with either GaAs0.8P0.2, Al0.15Ga0.85As, or GaAs barrier materials were grown by MOVPE on a nominally singular (001) GaAs substrate Ridge waveguide lasers, 25μm-wide and 1mm-long ridge, were fabricated and characterized under pulsed current conditions. The threshold current densities for devices are 5.9kA/cm2 and 5.8kA/cm2 for GaAsP barriers and Al0.15Ga0.85As barriers respectively, with a lasing wavelength of 960nm. Devices with GaAs barriers only lased at higher currents for a short wavelength transition ~900nm. While threshold currents are relatively high, no post growth thermal annealing was performed on these laser materials. Thermal annealing studies will be presented indicating significant improvement in QW luminescence and reduction in Jth can be achieved after the post-growth in-situ annealing. [1] Ludewig, P., Knaub, N., Hossain, N., Reinhard, S., Nattermann, L., Marko, I. P., and Volz, K. 2013. Appl. Phys. Lett., 102(24), 242115.

High temperature stability and high feedback-noise tolerance of the quantum dot lasers are advantageous features for application to silicon photonics. A silicon optical interposer with the bandwidth-density of 15Tbps/cm2 at 125 °C was demonstrated using flip-chip bonding method. Moreover, we report the first demonstration of a hybrid silicon quantum dot (QD) laser, evanescently coupled to a silicon waveguide. InAs/GaAs QD laser structures with thin AlGaAs lower cladding layers were transferred, by means of direct wafer bonding, onto silicon waveguides defining cavities with adiabatic taper structures and distributed Bragg reflectors (DBRs). The laser operates at temperatures up to 115 °C under pulsed current conditions, with a characteristic temperature T0 of 303 K near room temperature. Furthermore, by reducing the width of GaAs/AlGaAs mesa down to 8 μm, continuous-wave operation is realized at 25 °C.

High reflection dielectric distributed Bragg reflector (DBR) can be used with high Q optical cavity to narrow down the spectrum optical source, for experimental quantum electro-dynamics, etc. To construct a free space optical cavity for a local oscillator of the state-of-the-art optical frequency standards, concave mirrors are used as one of the end mirrors of the cavity. Usually, the high reflection DBR is fabricated by depositing dielectric materials on a glass substrate. However, the ultimate stability of the optical cavity is limited by the thermal noise of dielectric DBR. To overcome this problem, a crystalline DBR was proposed to stabilize the optical cavity, which can reduce thermal noise. In this study, we fabricated crystalline DBR by GaAs/AlAs compound semiconductor on a concave GaAs substrate. Although a traditional semiconductor substrate has atomically flat surface, we fabricated a concave surface with a curvature radius of 1000 mm on the GaAs substrate by optical quality polishing. Then, we carried out wet etching and introduced it in vacuum chamber for molecular beam epitaxy (MBE). In the MBE growth chamber, we carried out thermal cleaning with As4 at a substrate temperature of 600°C. Next, the GaAs/AlAs DBR structure was grown at 580°C. The evaluation of surface roughness was conducted by atomic force microscopy, which showed a roughness of 0.165 nm in 1 × 1 um measurement such that a very smooth surface can be obtained.

Quantum cascade (QC) lasers opens new prospects for powerful sources operating at THz frequencies. Up to now the best THz QC lasers are based on intersubband emission in GaAs/AlGaAs quantum well (QW) heterostructures. The maximum operating temperature is 200 K, which is too low for wide-spread applications. This is due to the rather low LO-phonon energy (36 meV) of GaAs-based materials. Indeed, thermal activation allows non-radiative path through electron-phonon interaction which destroys the population inversion. Wide band gap materials such as ZnO have been predicted to provide much higher operating temperatures because of the high value of their LO-phonon energy. However, despite some observations of intersubband absorption in c-plane ZnO/ZnMgO quantum wells, little is known on the fundamental parameters such as the conduction band offset in such heterostructures. In addition the internal field inherent to c-plane grown heterostuctures is an handicap for the design of QC lasers and detectors. In this talk, we will review a systematic investigation of ZnO/ZnMgO QW heterostructures with various Mg content and QW thicknesses grown by plasma molecular beam epitaxy on low-defect m-plane ZnO substrates. We will show that most samples exhibit TM-polarized intersubband absorption at room temperature linked either to bound-to-quasi bound inter-miniband absorption or to bound-to bound intersubband absorption depending on the Mg content of the barrier material. This systematic study allows for the first time to estimate the conduction band offset of ZnO/ZnMgO heterostructures, opening prospects for the design of QC devices operating at THz frequencies. This was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement #665107.

State of the art InGaP2/GaAs/In0.28Ga0.72As inverted metamorphic (IMM) solar cells have achieved impressive results, however, the thick metamorphic buffer needed between the lattice matched GaAs and lattice mismatched InGaAs requires significant effort and time to grow and retains a fairly high defect density. One approach to this problem is to replace the bottom InGaAs junction with an Sb-based material such as 0.73 eV GaSb or ~1.0 eV Al0.2Ga0.8Sb. By using interfacial misfit (IMF) arrays, the high degree of strain (7.8%) between GaAs and GaSb can be relaxed solely by laterally propagating 90° misfit dislocations that are confined to the GaAs-GaSb interface layer. We have used molecular beam epitaxy to grow GaSb single junction solar cells homoepitaxially on GaSb and heteroepitaxially on GaAs using IMF. Under 15-sun AM1.5 illumination, the control cell achieved 5% efficiency with a WOC of 366 mV, while the IMF cell was able to reach 2.1% with WOC of 546 mV. Shunting and high non-radiative dark current were main cause of FF and efficiency loss in the IMF devices. Threading dislocations or point defects were the expected source behind the losses, leading to minority carrier lifetimes less than 1ns. Deep level transient spectroscopy (DLTS) was used to search for defects electrically and two traps were found in IMF material that were not detected in the homoepitaxial GaSb device. One of these traps had a trap density of 7 × 1015 cm-3, about one order of magnitude higher than the control cell defect at 4 × 1016 cm-3.

The subband features E ‒ and E + for the conduction band of III-V dilute nitride alloys make them promising for intermediate band solar cell application. However, presence of bandgap states can limit the two-step photon absorption activity, a necessary requirement for IBSC functionality. A model analysis is performed to characterize the density of states. The sub-band tails states are characterized using a temperature-dependent map of photo-modulated reflectance spectroscopy for GaNAs thin films grown on GaAs substrates using molecular beam epitaxy. The effect of indium and antimony incorporation on the subband features were investigated. Marked improvements in the thin films were observed both for the lower ( E ‒ ) and the upper ( E+ ) conduction bands (CB) when In was introduced with marginal enhancement by Sb. These improvements are associated with suppression of tail states below both the E ‒ and E + bands. Sb rather mainly plays a surfactant role improving the abruptness of the GaNAs/GaAs hetero-interface.

The flawed surface of GaAs/GaAlAs heterointerface after wet etching by H 2 O 2 and NH 4 OH based etch ant was studied in this work. The results showed that the surface of GaAs/GaAlAs heterointerface had convex point, etching pits, pinhole, fog point, and friction scratches were investigated with a etch step measurement. And imprinting the main reasons for the formation of the etching surface defects of GaAs/GaAlAs are the poor quality of epitaxial materials, the contamination of materials surface, the unclear interface of oxidation and doping, the inhomogeneity of concentration and the operation errors. The selective etching of the GaAs/GaAlAs material eliminates some flaws and improves the quality of the etching surface of the GaAs/GaAlAs material.

The electronic structure and optical properties of pure and P-doped cubic-blende gallium arsenide (GaAs) for different P constants (x=0, 0.125, 0.25, 0.375) have been studied by the first-principles projected augmented plane potential approach based on the density functional theory and the generalized gradient approximation method. It shows that the P-doped material has a smaller lattice constant, which resulted in a local lattice distortion. The minimum of the conduction band moves to high energy level and the band gaps gradually become wide with gradual increase concentration of P impurity. The dielectric function are calculated based on Kramers-Kroning relations. The optical property studied from the calculated absorption coefficients shows that the adsorption peaks change obviously in the visible light wavelength area for the P-doped GaAs system.

To strive for the goal of further improving the overall performance of low-light-level Gen.Ⅲ image intensifier tube, modifications and innovations in the making of GaAs photocathode are already underway revolving around the basis of existing research, through which the sensitivity of GaAs photocathode is considerably improved from 1200μA/lm to above 1800μA/lm, 2000μA/lm (typical value), and it won’t drop within the 1000hrs’ storage inside the station according to the experiment on the photoemission stability of high-sensitivity GaAs photocathode. In short, highly distinguished characteristics of high sensitivity GaAs photocathode like wide response range, superior quantum efficiency and 1.06μm infrared response wavelength, promise its remarkable significance in both the enhancement of the overall performance and the prolongation of the operational life-span of low-lightlevel Gen.Ⅲ image intensifier tube.

Substrate-emitting GaAs based oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with top-surface high-frequency ground-source-ground contact pads are designed, fabricated, and characterized. The devices are composed of standard top and bottom epitaxially-grown AlGaAs distributed Bragg reflectors (DBRs). The top (p)DBR is capped with p-contact Ti then Au thin-film metals for uniform current injection and laser emission is through the GaAs substrate. The devices are realized on a single epitaxial wafer with n-ohmic-contacts placed on a thick (n+)GaAs buffer layer beneath the bottom (n)DBR and alternatively with the n-ohmic-contacts placed on an (n)GaAs intra-cavity layer lying within the same bottom (n)DBR. Static device parameters including threshold current and rollover current, differential resistance, peak optical output power, and wall-plug efficiency are extracted for VCSELs with oxide-aperture diameters ranging from about 3 to 9-µm and at different temperatures. At room temperature threshold currents are achieved from the sub-mA range up to about 3.5-mA with maximum output powers exceeding 15-mW. Increasing the temperature up to 85 °C slightly increases the threshold current while the peak output power is about halved. The differential resistance at the thermal rollover current is comparable for standard and intra-cavity n-metal-contacts. Small-signal analysis is performed for different bias currents, temperatures, oxide-aperture diameters, and the two n-contact options. Under optimal bias conditions the 3-dB bandwidth exceeds 15 GHz. Direct current modulation-based on-off keying signal generation is investigated from 10 to 40-Gb/s. The influence of an anti-reflection-coated substrate, a thinned substrate, and the combination of both is investigated and discussed.