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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A method is provided for the fabrication of a photovoltaic device which possesses an efficient collector system for the conduction of the current generated by incident photons to the external circuitry of the device.
The ultimate objective of the thin-film program at NASA GRC is development of a 20 percent AM0 thin-film device technology with high power/weight ratio. Several approaches are outlined to improve overall device efficiency and power/weight ratio. One approach involves the use of very lightweight flexible substrates such as polyimides (i.e., Kapton(Trademark)) or metal foil. Also, a compound semiconductor tandem device structure that can meet this objective is proposed and simulated using Analysis of Microelectronic and Photonic Structures (AMPS). AMPS modeling of current devices in tandem format indicate that AM0 efficiencies near 20 percent can be achieved. And with improvements in materials, efficiencies approaching 25 percent are achievable. Several important technical issues need to be resolved to realize these complex devices: development of a wide bandgap material with good electronic properties, development of transparent contacts, and targeting a 2-terminal device structure (with more complicated processing and tunnel junction) or 4-terminal device. Recent progress in the NASA GRC program is outlined.
ZnBeO and ZnCdSeO alloys have been disclosed as materials for the improvement in performance, function, and capability of semiconductor devices. The alloys can be used alone or in combination to form active photonic layers that can emit over a range of wavelength values. Materials with both larger and smaller band gaps would allow for the fabrication of semiconductor heterostructures that have increased function in the ultraviolet (UV) region of the spectrum. ZnO is a wide band-gap material possessing good radiation-resistance properties. It is desirable to modify the energy band gap of ZnO to smaller values than that for ZnO and to larger values than that for ZnO for use in semiconductor devices. A material with band gap energy larger than that of ZnO would allow for the emission at shorter wavelengths for LED (light emitting diode) and LD (laser diode) devices, while a material with band gap energy smaller than that of ZnO would allow for emission at longer wavelengths for LED and LD devices. The amount of Be in the ZnBeO alloy system can be varied to increase the energy bandgap of ZnO to values larger than that of ZnO. The amount of Cd and Se in the ZnCdSeO alloy system can be varied to decrease the energy band gap of ZnO to values smaller than that of ZnO. Each alloy formed can be undoped or can be p-type doped using selected dopant elements, or can be n-type doped using selected dopant elements. The layers and structures formed with both the ZnBeO and ZnCdSeO semiconductor alloys - including undoped, p-type-doped, and n-type-doped types - can be used for fabricating photonic and electronic semiconductor devices for use in photonic and electronic applications. These devices can be used in LEDs, LDs, FETs (field effect transistors), PN junctions, PIN junctions, Schottky barrier diodes, UV detectors and transmitters, and transistors and transparent transistors. They also can be used in applications for lightemitting display, backlighting for displays, UV and visible transmitters and detectors, high-frequency radar, biomedical imaging, chemical compound identification, molecular identification and structure, gas sensors, imaging systems, and for the fundamental studies of atoms, molecules, gases, vapors, and solids.
While conventional homoepitaxy forms high-quality epitaxial layers, the limited set of material systems for commercially available wafers restricts the range of materials that can be grown homoepitaxially. At the same time, conventional heteroepitaxy of lattice-mismatched systems produces dislocations above a critical strain energy to release the accumulated strain energy as the film thickness increases. The formation of dislocations, which severely degrade electronic/photonic device performances, is fundamentally unavoidable in highly lattice-mismatched epitaxy. Herein, we introduce a unique mechanism of relaxing misfit strain in heteroepitaxial films that can enable effective lattice engineering. We have observed that heteroepitaxy on graphene-coated substrates allows for spontaneous relaxation of misfit strain owing to the slippery graphene surface while achieving single-crystalline films by reading the atomic potential from the substrate. This spontaneous relaxation technique could transform the monolithic integration of largely lattice-mismatched systems by covering a wide range of the misfit spectrum to enhance and broaden the functionality of semiconductor devices for advanced electronics and photonics.
The selenium substitution strategy was applied to develop two new A′-DAD-A′-type small molecular acceptors. The resulting selenium-incorporated molecules exhibit red-shifted absorption and an enhanced photon response, leading to high device efficiencies of over 16%.
Trapped magnetic vortices in niobium introduce microwave losses that degrade the performance of superconducting resonators. While such losses have been extensively studied above 1 K, we report here their direct quantification in the millikelvin and low-photon regime relevant to quantum devices. Using a high-quality factor 3D niobium cavity cooled through its superconducting transition in controlled magnetic fields, we isolate vortex-induced losses and find the resistive component of the sensitivity to trapped flux S to be approximately 2 n Ω/mG at 10 mK and 6 GHz. The decay rate is initially dominated by two-level system (TLS) losses from the native niobium pentoxide, with vortex-induced degradation of T 1 occurring above B trap ∼ 50 mG. In the absence of the oxide, even 10 mG of trapped flux limits performance, Q 0 ∼ 10 10 , or T 1 ∼ 350 ms, underscoring the need for stringent magnetic shielding. The resistive sensitivity, S, decreases with temperature and remains largely field-independent, whereas the reactive component, S′, exhibits a maximum near 0.8 K. These behaviors are well modeled within the Coffey–Clem framework in the zero-creep limit, under the assumption that vortex pinning is enhanced by thermally activated processes. Our results suggest that niobium-based transmon qubits can tolerate vortex-induced dissipation at trapped field levels up to several hundred mG, but achieving long coherence times still requires careful magnetic shielding to suppress lower-field losses from other mechanisms.
In the 4th generation of X-ray light sources, including Free-Electron Lasers (FEL) and Diffraction-Limited Storage Rings (DLSR), the emittance of the electron beam is small or negligible compared to the emittance of the photon beam produced by insertion devices, thus generating coherent beams of light. Over the next few years, several lightsource facilities will be built or upgraded to produce X-ray beams of unprecedented coherent flux. Delivering these exceptional beams to the sample chambers requires beamline optical systems that are designed to preserve the wavefront properties. Our goal in the Advanced Light Source upgrade project (ALS-U) is to create a new class of beamlines that reach diffraction-limited X-ray optical quality through tightly integrated, efficient optical systems, diagnostics, and adaptive mirrors, thus providing users with new scientific capabilities offered by coherent X-ray light interactions with matter. Herein we describe aspects of the beamlines’ design as they enter the project’s final design phase.
Controlling interlayer excitons in Van der Waals heterostructures holds promise for exploring Bose-Einstein condensates and developing novel optoelectronic applications, such as excitonic integrated circuits. Despite intensive studies, several key fundamental properties of interlayer excitons, such as their binding energies and interactions with charges, remain not well understood. Here we report the formation of momentum-direct interlayer excitons in a high-quality MoSe 2 /hBN/MoSe 2 heterostructure under an electric field, characterized by bright photoluminescence (PL) emission with high quantum yield and a narrow linewidth of less than 4 meV. These interlayer excitons show electrically tunable emission energy spanning ~180 meV through the Stark effect, and exhibit a sizable binding energy of ~81 meV in the intrinsic regime, along with trion binding energies of a few millielectronvolts. Remarkably, we demonstrate the long-range transport of interlayer excitons with a characteristic diffusion length exceeding 10 μm, which can be attributed, in part, to their dipolar repulsive interactions. Further, spatially and polarization-resolved spectroscopic studies reveal rich exciton physics in the system, such as valley polarization, local trapping, and the possible existence of dark interlayer excitons. Furthermore, the formation and transport of tightly bound interlayer excitons with narrow linewidth, coupled with the ability to electrically manipulate their properties, open exciting new avenues for exploring quantum many-body physics, including excitonic condensate and superfluidity, and for developing novel optoelectronic devices, such as exciton and photon routers.
Trapped magnetic vortices in niobium introduce microwave losses that degrade the performance of superconducting resonators. While such losses have been extensively studied above 1 K, we report here their direct quantification in the millikelvin and low-photon regime relevant to quantum devices. Using a high-quality factor 3D niobium cavity cooled through its superconducting transition in controlled magnetic fields, we isolate vortex-induced losses and find the resistive component of the sensitivity to trapped flux S to be approximately 2 nOhm/mG at 10 mK and 6 GHz. The decay rate is initially dominated by two-level system (TLS) losses from the native niobium pentoxide, with vortex-induced degradation of T1 occurring above Btrap~50 mG. In the absence of the oxide, even 10 mG of trapped flux limits performance, Q0 ~ 1010, or T1 ~350 ms, underscoring the need for stringent magnetic shielding. The resistive sensitivity, S, decreases with temperature and remains largely field-independent, whereas the reactive component, S , exhibits a maximum near 0.8 K. These behaviors are well modeled within the Coffey Clem framework in the zero-creep limit, under the assumption that vortex pinning is enhanced by thermally activated processes. Our results suggest that niobium-based transmon qubits can tolerate vortex-induced dissipation at trapped field levels up to several hundred mG, but achieving long coherence times still requires careful magnetic shielding to suppress lower-field losses from other mechanisms
Research toward practical implementation of the Intensified Charge Coupled Device (ICCD) as a photon-counting array detector for astronomy is reported. The first area of concentration was to determine the rate and extent of the lifetime limiting damage to the CCD caused by the impact of high energy electrons, and to find whether various methods of annealing the damage were productive. The second effort was to determine the performance of the ICCD in a photon-counting mode to produce extended dynamic range measurements. There are two main effects that appear as the practical results of the electron damage to the CCD. One is an increase in the leakage current, i.e., the normal thermal generation of charge carriers in the silicon that provides a background dark signal that adds to the light produced image. In an undamaged CCD, the leakage current is usually fairly uniform across the photosensitive area of the silicon chip, with the exception of various bright pixels which have an anomalous leakage current well above the overall level.
SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than plus or minus 10 deg.) sapphire (0001) substrate can be used to improve epitaxial relationships better by providing attractive atomic steps in the epitaxial process.
The function of the infrared gas transducer used during extravehicular activity (EVA) in the current space suit is to measure and report the concentration of carbon dioxide (CO2) in the ventilation loop. The next generation portable life support system (PLSS) requires highly accurate CO2 sensing technology with performance beyond that presently in use on the International Space Station extravehicular mobility unit (EMU). Further, that accuracy needs to be provided over the full operating pressure range of the suit (3 to 25 psia). Accommodation within space suits demands that optical sensors meet stringent size, weight, and power requirements. A laser diode (LD) sensor based on infrared absorption spectroscopy is being developed for this purpose by Vista Photonics, Inc. Version 1.0 prototype devices were delivered to NASA Johnson Space Center (JSC) in September 2011. The prototypes were upgraded with more sophisticated communications and faster response times to version 2.0 and delivered to JSC in July 2012. The sensors incorporate a laser diode based CO2 channel that also includes an incidental water vapor (humidity) measurement. The prototypes are controlled digitally with an field-programmable gate array microcontroller architecture. Based on the results of the iterative instrument development, further prototype development and testing of instruments were performed leveraging the lessons learned where feasible. The present development extends and upgrades the earlier hardware for the advanced PLSS 2.5 prototypes for testing at JSC. The prototypes provide significantly enhanced accuracy for water vapor measurement and eliminate wavelength drift affecting the earlier versions. Various improvements to the electronics and gas sampling are currently being advanced including the companion development of engineering development units that will ultimately be capable of radiation tolerance. The combination of low power electronics with the performance of a long wavelength laser spectrometer enables multi-gas sensors with significantly increased performance over that presently offered in the EMU.
Kinetic inductance detectors (KID) have received increased interest due to their relative ease of fabrication, low noise, and scalability to large format arrays required by next generation of astronomical telescopes. The development of KIDs has progressed rapidly, with very low noise equivalent power demonstrated by several groups and KIDs arrays implemented in several ground-based and air-borne instruments. In this paper, we describe a new fabrication process which consists of a membrane isolated KID incorporating a phononic bandgap structure tuned to block recombination phonons from escaping to the thermal bath. This architecture is designed to increase the quasi-particle lifetime and results in increased responsivity to signal photons and lower noise. These devices have been fabricated as lumped-element resonators with hafnium inductors and Nb capacitors on low stress silicon nitride and silicon-on-insulator membranes. We discuss the fabrication process, which uses a combination of sub-micron laser based direct write lithography and nanoscale electron beam lithography.
This is the final report for this project. The major objectives were to develop full models and standard cells of CMOS silicon photomultipliers (SiPM) for neutron detection applications. Specifically, the research seeks to replace photomultiplier tubes, used in neutron detection applications, with SiPMs containing integrated readout electronics fabricated in standard CMOS processes. The detectors improve on the detection efficiency, readout speed, resolution (sensitivity), and spatial resolution of current systems. In particular, this work involved collaboration with the instrument and detector group at ORNL who build detectors based on discrete commercially available PMTs and SiPMs. The SiPM detectors developed in this work are based on Perimeter Gated Single Photon Avalanche Diodes (PGSPAD). These devices have tunable breakdown voltage which affects other performance characteristics of the detectors. The ability of the detectors to have integrated readout and tune the noise floor and dynamic range in addition to offering a method for non-uniformity compensation in a compact form significantly impacts the imaging research field and includes the nuclear sciences field, circuits and systems field in addition to varied fields such as geography and biology/medicine.
Damage by radiation healed rapidly. Feature provides continuous, rapid recovery of devices from degradation caused by hot electrons, photons, and ionizing radiation. Several candidate sites for palladium film catalysts, inserted during manufacture as integral parts of devices. Paladium films made by evaporation, sputtering, or chemical-vapor deposition. If additional storage required, thick layer of palladium plated on inside of package surrounding device. Hydrogen stored by exposing palladium to hydrogen gas just before package sealed hermetically.
Epitaxial layers with varying donor concentration profiles were grown on silicon substrate wafers using chemical vapor deposition (CVD) techniques, and solid state photomultiplier (SSPM) devices were fabricated from the wafers. Representative detectors were tested in a low background photon flux, low temperature environment to determine the device characteristics for comparison to NASA goals for astronomical applications. The SSPM temperatures varied between 6 and 11 K with background fluxes in the range from less than 5 x 10 to the 6th power to 10 to the 13th power photons/square cm per second at wavelengths of 3.2 and 20 cm. Measured parameters included quantum efficiency, dark count rate and bias current. Temperature for optimal performance is 10 K, the highest ever obtained for SSPMs. The devices exhibit a combination of the lowest dark current and highest quantum efficiency yet achieved. Experimental data were reduced, analyzed and used to generate recommendations for future studies. The background and present status of the microscopic theory of SSPM operation were reviewed and summarized. Present emphasis is on modeling of the avalanche process which is the basis for SSPM operation. Approaches to the solution of the Boltzmann transport equation are described and the treatment of electron scattering mechanisms is presented. The microscopic single-electron transport theory is ready to be implemented for large-scale computations.
A proposal has been made to exploit the special wavelength-dispersive characteristics of devices of the type described in One-Dimensional Photonic Crystal Superprisms (NPO-30232) NASA Tech Briefs, Vol. 29, No. 4 (April 2005), page 10a. A photonic crystal is an optical component that has a periodic structure comprising two dielectric materials with high dielectric contrast (e.g., a semiconductor and air), with geometrical feature sizes comparable to or smaller than light wavelengths of interest. Experimental superprisms have been realized as photonic crystals having three-dimensional (3D) structures comprising regions of amorphous Si alternating with regions of SiO2, fabricated in a complex process that included sputtering. A photonic crystal of the type to be exploited according to the present proposal is said to be one-dimensional (1D) because its contrasting dielectric materials would be stacked in parallel planar layers; in other words, there would be spatial periodicity in one dimension only. The processes of designing and fabricating 1D photonic crystal superprisms would be simpler and, hence, would cost less than do those for 3D photonic crystal superprisms. As in 3D structures, 1D photonic crystals may be used in applications such as wavelength-division multiplexing. In the extended-range configuration, it is also suitable for spectrometry applications. As an engineered structure or artificially engineered material, a photonic crystal can exhibit optical properties not commonly found in natural substances. Prior research had revealed several classes of photonic crystal structures for which the propagation of electromagnetic radiation is forbidden in certain frequency ranges, denoted photonic bandgaps. It had also been found that in narrow frequency bands just outside the photonic bandgaps, the angular wavelength dispersion of electromagnetic waves propagating in photonic crystal superprisms is much stronger than is the angular wavelength dispersion obtained by use of conventional prisms and diffraction gratings and is highly nonlinear.
CCD imaging arrays were evaluated for a photon counting astronomical sensor. Results show noise corresponding to less than 100 rms electrons and gains of approximately 1000 at 10kV accelerating voltage (greater than 5000 at 25kV). Measured charge transfer efficiencies are in excess of 0.9999, signal saturation levels are as high as 990000 electrons per pixel and peak quantum efficiencies are greater than 75%. Successful proximity focussed intensified charge coupled devices (ICCD) have been fabricated, although problems still exist with contamination and possible structural failures in the CCD's during tube manufacture.