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At least 307 records · Page 17

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DOE OSTI2022

Significant improvement of conversion efficiency by passivation of low-angle grain boundaries in flexible low-cost single-crystal-like GaAs thin-film solar cells directly deposited on metal tape

We develop an easily implementable yet effective process to achieve high power conversion efficiency in newly-developed flexible single-crystal-like GaAs thin-film photovoltaic solar cells on cheap metal tape. We study various techniques on the fabricated devices to passivate the defect states associated with dangling bonds at low-angle grain boundaries (LA-GBs) existing in the single-crystal-like GaAs material. We report that sulfur by trioctylphosphine sulfide (TOP:S) solution treatment can partially but effectively passivate the defect states at the LA-GBs to increase all the solar cell performance parameters of open-circuit voltage VOC (33.2%), short-circuit current JSC (19.5%), and fill factor FF (25.8%), resulting in the improvement of the power conversion efficiency more than double. The material and device characterizations and numerical modeling are performed to propose a mechanism, also suggesting that the power conversion efficiency higher than 20%, which is an important target milestone in emerging solar cell technologies, can be achieved. This work presents the first effective passivation of the bulk defects in GaAs at the device level and can also offer a solution for other photonic and electronic devices using non-single-crystalline GaAs films for flexible electronics.

36 MATERIALS SCIENCE↗

NASA NTRS2009

Silicon Nanowire Growth at Chosen Positions and Orientations

It is now possible to grow silicon nanowires at chosen positions and orientations by a method that involves a combination of standard microfabrication processes. Because their positions and orientations can be chosen with unprecedented precision, the nanowires can be utilized as integral parts of individually electronically addressable devices in dense arrays. Nanowires made from silicon and perhaps other semiconductors hold substantial promise for integration into highly miniaturized sensors, field-effect transistors, optoelectronic devices, and other electronic devices. Like bulk semiconductors, inorganic semiconducting nanowires are characterized by electronic energy bandgaps that render them suitable as means of modulating or controlling electronic signals through electrostatic gating, in response to incident light, or in response to molecules of interest close to their surfaces. There is now potential for fabricating arrays of uniform, individually electronically addressable nanowires tailored to specific applications. The method involves formation of metal catalytic particles at the desired positions on a substrate, followed by heating the substrate in the presence of silane gas. The figure illustrates an example in which a substrate includes a silicon dioxide surface layer that has been etched into an array of pillars and the catalytic (in this case, gold) particles have been placed on the right-facing sides of the pillars. The catalytic thermal decomposition of the silane to silicon and hydrogen causes silicon columns (the desired nanowires) to grow outward from the originally catalyzed spots on the substrate, carrying the catalytic particles at their tips. Thus, the position and orientation of each silicon nanowire is determined by the position of its originally catalyzed spot on the substrate surface, and the orientation of the nanowire is perpendicular to the substrate surface at the originally catalyzed spot.

Getty, Stephanie A.↗

NASA NTRS2016

Photonic Integrated Circuit (PIC) Device Structures: Background, Fabrication Ecosystem, Relevance to Space Systems Applications, and Discussion of Related Radiation Effects

Electronic integrated circuits are considered one of the most significant technological advances of the 20th century, with demonstrated impact in their ability to incorporate successively higher numbers transistors and construct electronic devices onto a single CMOS chip. Photonic integrated circuits (PICs) exist as the optical analog to integrated circuits; however, in place of transistors, PICs consist of numerous scaled optical components, including such "building-block" structures as waveguides, MMIs, lasers, and optical ring resonators. The ability to construct electronic and photonic components on a single microsystems platform offers transformative potential for the development of technologies in fields including communications, biomedical device development, autonomous navigation, and chemical and atmospheric sensing. Developing on-chip systems that provide new avenues for integration and replacement of bulk optical and electro-optic components also reduces size, weight, power and cost (SWaP-C) limitations, which are important in the selection of instrumentation for specific flight projects. The number of applications currently emerging for complex photonics systems-particularly in data communications-warrants additional investigations when considering reliability for space systems development. This Body of Knowledge document seeks to provide an overview of existing integrated photonics architectures; the current state of design, development, and fabrication ecosystems in the United States and Europe; and potential space applications, with emphasis given to associated radiation effects and reliability.

Body of Knowledge (BOK)↗

NASA NTRS1992

An overview of silicon carbide device technology

Recent progress in the development of silicon carbide (SiC) as a semiconductor is briefly reviewed. This material shows great promise towards providing electronic devices that can operate under the high-temperature, high-radiation, and/or high-power conditions where current semiconductor technologies fail. High quality single crystal wafers have become available, and techniques for growing high quality epilayers have been refined to the point where experimental SiC devices and circuits can be developed. The prototype diodes and transistors that have been produced to date show encouraging characteristics, but by the same token they also exhibit some device-related problems that are not unlike those faced in the early days of silicon technology development. Although these problems will not prevent the implementation of some useful circuits, the performance and operating regime of SiC electronics will be limited until these device-related issues are solved.

Neudeck, Philip G.↗

DOE OSTI2024

Controlling structure and interfacial interaction of monolayer TaSe2 on bilayer graphene

Abstract Tunability of interfacial effects between two-dimensional (2D) crystals is crucial not only for understanding the intrinsic properties of each system, but also for designing electronic devices based on ultra-thin heterostructures. A prerequisite of such heterostructure engineering is the availability of 2D crystals with different degrees of interfacial interactions. In this work, we report a controlled epitaxial growth of monolayer TaSe 2 with different structural phases, 1 H and 1 T , on a bilayer graphene (BLG) substrate using molecular beam epitaxy, and its impact on the electronic properties of the heterostructures using angle-resolved photoemission spectroscopy. 1 H -TaSe 2 exhibits significant charge transfer and band hybridization at the interface, whereas 1 T -TaSe 2 shows weak interactions with the substrate. The distinct interfacial interactions are attributed to the dual effects from the differences of the work functions as well as the relative interlayer distance between TaSe 2 films and BLG substrate. The method demonstrated here provides a viable route towards interface engineering in a variety of transition-metal dichalcogenides that can be applied to future nano-devices with designed electronic properties.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Smart Meter Pinging and Reading Through AMI Two-Way Communication Networks to Monitor Grid Edge Devices and DERs

Today’s power distribution system is changing to a power-electronics-enabled distribution system, especially with the increasing penetration of distributed energy resources (DERs). To monitor and manage those electronic devices and DERs at the grid edge, the advanced metering infrastructure (AMI) with two-way communications presents great potential. At present, extensive research explores the upstream communication from smart meters to electric utilities (e.g., meter reading) but few examine the downstream communication from the utilities to smart meters (e.g., meter pinging). This article discusses the AMI two-way communication and its recent industrial practice in the U.S., especially for applying the smart meter pinging functionality to monitor grid-edge devices and DERs. This paper then develops the two-way communication model and the network calculus method to quantify the impact of the two-way communication on the AMI network. In the end, the proposed method is validated with ns-3 simulation using the modified 13-node test feeder and real-world feeder systems.

24 POWER TRANSMISSION AND DISTRIBUTION↗

NASA NTRS1995

Storing Data In Circulating Electrons

Proposed memory device contains electrons traveling in circular orbit in vacuum. Orientations of electron spins (up or down) represents binary ones or zeros, respectively. Assuming length of each memory element 100 times classical fictitious electron radius, device theoretically capable of storing 446 gigabytes of data per meter of circumference of orbit.

Eastman, Ted R.↗

NASA NTRS1999

Silicon Carbide Being Developed for High-Definition Television (HDTV) Transmitter Modules

Through a Space Act Agreement, the NASA Lewis Research Center has helped develop the base silicon carbide (SiC) epitaxial growth technology for Westinghouse's efforts to bring silicon carbide products to the marketplace. SiC is a high-temperature, high-voltage semiconductor that can deliver greater than three times the power of conventional silicon devices. The technology was initially disclosed in the 1994 R&T report. NASA Lewis High Temperature Integrated Electronics and Sensors (HTIES) team is developing SiC as a material for advanced semiconductor electronic device applications because SiC-based electronics and sensors can operate in hostile environments where conventional silicon-based electronics cannot function. SiC transmitters hold great promise for television stations because they can convert broadcasts from analog to digital signals. A modular solid-state design provides broadcasters with an option to gradually add modules, increasing the power of their transmitters as they expand their high-definition television (HDTV) coverage. Using these high-power transistors will significantly reduce the space needed for high-power transmitters at television stations and will offer a solid-state solution, reducing long-term maintenance costs. Thus, transmitter manufacturers will be able to abandon their reliance on tube-based technology for high-power transmitters and will be able to build smaller, high-power, solid-state transmitters.

Costello, Donald E.↗

NASA NTRS1985

Defects in silicon effect on device performance and relationship to crystal growth conditions

A relationship between material defects in silicon and the performance of electronic devices will be described. A role which oxygen and carbon in silicon play during the defects generation process will be discussed. The electronic properties of silicon are a strong function of the oxygen state in the silicon. This state controls mechanical properties of silicon efficiency for internal gettering and formation of defects in the device's active area. In addition, to temperature, time, ambience, and the cooling/heating rates of high temperature treatments, the oxygen state is a function of the crystal growth process. The incorporation of carbon and oxygen into silicon crystal is controlled by geometry and rotation rates applied to crystal and crucible during crystal growths. Also, formation of nucleation centers for oxygen precipitation is influenced by the growth process, although there is still a controversy which parameters play a major role. All these factors will be reviewed with special emphasis on areas which are still ambiguous and controversial.

Jastrzebski, L.↗

DOE OSTI2025

In-device Battery Failure Analysis

Lithium-ion batteries are indispensable power sources for a wide range of modern electronic devices. However, battery lifespan remains a critical limitation, directly affecting the sustainability and user experience. Conventional battery failure analysis in controlled lab settings may not capture the complex interactions and environmental factors encountered in real-world, in-device operating conditions. Here, this study analyzes the failure of commercial wireless earbud batteries as a model system within their intended usage context. Through multiscale and multimodal characterizations, the degradations from the material level to the device level are correlated, elucidating a failure pattern that is closely tied to the specific device configuration and operating conditions. The findings indicate that the ultimate failure mode is determined by the interplay of battery materials, cell structural design, and the in-device microenvironment, such as temperature gradients and their fluctuations. This holistic, in-device perspective on environmental influences provides critical insights for battery integration design, enhancing the reliability of modern electronics.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Thermal Conductivity of β-Phase Ga 2 O 3 and (Al x Ga 1– x ) 2 O 3 Heteroepitaxial Thin Films

Heteroepitaxy of β-phase gallium oxide (β-Ga 2 O 3 ) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of ($\bar{2}01$)-oriented β-Ga 2 O 3 heteroepitaxial thin films were investigated. Unintentionally doped β-Ga 2 O 3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward $\langle$$11\bar{2}0$$\rangle$ via metal–organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga 2 O 3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga 2 O 3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga 2 O 3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye–Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga 2 O 3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga 2 O 3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga 2 O 3 /sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown ($\bar{2}01$)-oriented β-(Al x Ga 1–x ) 2 O 3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(Al x Ga 1–x ) 2 O 3 films exhibit lower thermal conductivities (2.8–4.7 W/m∙K) than the β-Ga 2 O 3 thin films. The dominance of the alloy disorder scattering in β-(Al x Ga 1–x ) 2 O 3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga 2 O 3 and (Al x Ga 1–x ) 2 O 3 thin films and lays the groundwork for the thermal modeling and design of β-Ga 2 O 3 electronic and optoelectronic devices.

36 MATERIALS SCIENCE↗

NASA NTRS1998

Electronic Properties of Carbon Nanotubes and Junctions

Metallic and semiconducting Single Wall Carbon Nanotubes (CNT) have recently been characterized using scanning tunneling microscopy (STM) and the manipulation of individual CNT has been demonstrated. These developments make the prospect of using CNT as molecular wires and possibly as electronic devices an even more interesting one. We have been modeling various electronic properties such as the density of states and the transmission coefficient of CNT wires and junctions. These studies involve first calculating the stability of junctions using molecular dynamics simulations and then calculating the electronic properties using a pi-electron tight binding Hamiltonian. We have developed the expertise to calculate the electronic properties of both finite-sized CNT and CNT systems with semi-infinite boundary conditions. In this poster, we will present an overview of some of our results. The electronic application of CNT that is most promising at this time is their use as molecular wires. The conductance can however be greatly reduced because of reflection due to defects and contacts. We have modeled the transmission through CNT in the presence of two types of defects: weak uniform disorder and strong isolated scatterers. We find that the conductance is affected in significantly different manners due to these defects Junctions of CNT have also been imaged using STM. This makes it essential to derive rules for the formation of junctions between tubes of different chirality, study their relative energies and electronic properties. We have generalized the rules for connecting two different CNT and have calculated the transmission and density of states through CNT junctions. Metallic and semiconducting CNT can be joined to form a stable junction and their current versus voltage characteristics are asymmetric. CNT are deformed by the application of external forces including interactions with a substrate or other CNT. In many experiments, these deformation are expected to occur naturally. We will present some preliminary results of our calculations of the modification of CNT electronic properties as a result of deformations.

Anantram, M. P.↗

NASA NTRS1993

Electron Microscopy of Natural and Epitaxial Diamond

Semiconducting diamond films have the potential for use as a material in which to build active electronic devices capable of operating at high temperatures or in high radiation environments. Ultimately, it is preferable to use low-defect-density single crystal diamond for device fabrication. We have previously investigated polycrystalline diamond films with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and homoepitaxial films with SEM-based techniques. This contribution describes some of our most recent observations of the microstructure of natural diamond single crystals and homoepitaxial diamond thin films using TEM.

Posthill, J. B.↗

NASA NTRS2014

Structural Assembly for Cold Plate Cooling

A device including a structural member having a heat spreader and an electronic device mounted directly to a first surface of the heat spreader of the structural member. The device also includes a cold plate mounted directly to the first surface of the heat spreader of the structural member.

Zaffetti, Mark A.↗

DOE OSTI2020

Growth and characterization of homoepitaxial β-Ga 2 O 3 layers

ß-Ga 2 O 3 is a next-generation ultra-wide bandgap semiconductor (E g = 4.8 eV to 4.9 eV) that can be homoepitaxially grown on commercial substrates, enabling next-generation power electronic devices among other important applications. Analyzing the quality of deposited homoepitaxial layers used in such devices is challenging, in part due to the large probing depth in traditional x-ray diffraction (XRD) and also due to the surface-sensitive nature of atomic force microscopy (AFM). Here, a combination of evanescent grazing-incidence skew asymmetric XRD and AFM are investigated as an approach to effectively characterize the quality of homoepitaxial ß-Ga 2 O 3 layers grown by molecular beam epitaxy at a variety of Ga/O flux ratios. Accounting for both structure and morphology, optimal films are achieved at a Ga/O ratio of ~1.15, a conclusion that would not be possible to achieve by either XRD or AFM methods alone. Finally, fabricated Schottky barrier diodes with thicker homoepitaxial layers are characterized by J-V and C-V measurements, revealing an unintentional doping density of 4.3×10 16 cm -3 - 2×10 17 cm -3 in the epilayer. These results demonstrate the importance of complementary measurement methods for improving the quality of the ß-Ga 2 O 3 homoepitaxial layers used in power electronic and other devices.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Competition between magnetic order and charge localization in Na 2 IrO 3 thin crystal devices thin crystal devices

Spin orbit assisted Mott insulators such as sodium iridate (Na 2 IrO 3 ) have been an important subject of study in recent years. In these materials, the interplay of electronic correlations, spin-orbit coupling, crystal field effects, and a honeycomb arrangement of ions bring exciting ground states, predicted in the frame of the Kitaev model. The insulating character of Na 2 IrO 3 has hampered its integration to an electronic device, desirable for applications, such as the manipulation of quasiparticles interesting for topological quantum computing. Here we show through electronic transport measurements supported by angle-resolved photoemission spectroscopy (ARPES) experiments, that electronic transport in Na 2 IrO 3 is ruled by variable range hopping and it is strongly dependent on the magnetic ordering transition known for bulk Na 2 IrO 3 , as well as on external electric fields. Furthermore, electronic transport measurements allow us to deduce a value for the localization length and the density of states in our Na 2 IrO 3 thin crystal devices, and offer an alternative approach to study insulating 2D-materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Interplay of electronic structure, magnetism, strain, and defects in carbide $\mathrm{MX}$enes

We report the two-dimensional (2D) magnetic and semiconducting materials, including carbide MXenes, are in high demand for magneto-electronic devices and applications. Here, we report a first-principles study of electronic structure and magnetism of a Ti 2 C MXene, its derivatives Ti 2 CT 2 (T = -F, -O, -OH, -H), and the effect of single vacancy defects (25% C, 12.5% O, and 12.5% and 5.5% Ti) and transition metal (V, Cr, Mn, and Co) dopings. The MAX phase Ti 2 AlC is a non-magnetic (NM) metal which upon removal of Al layer forms a pristine Ti 2 C MXene with A-type antiferromagnetic (AFM) semiconductor having reliable transition temperature (T N = 41K) predicted by the Heisenberg model. All the functionalized MXenes are stable as NM metal except for Ti 2 CO 2 which remains semiconducting with NM ground state. The significant effect of spin–orbit coupling (SOC) is evident in the band structure forming Dirac-like cones and band inversions near the Fermi level. Depending upon the type of vacancy defects Ti 2 CO 2 is NM metal and ferromagnetic (FM) metal. The transition metal (TM) doped MXenes fulfill FM Stoner criterion. The V- and Co-doped MXenes are metals, whereas Cr- and Mn-doped are half-metal and semiconductor.

2D magnetism↗

DOE OSTI2023

SiC Microchannel Heat Sinks for High Heat Flux Dissipation of 1 kW/cm 2

Thermal management has become a major barrier in the development of high-power micro-devices. Microchannel heat sinks (MCHS) are a promising method to dissipate high heat fluxes from high power density devices. Reducing the thermal resistance will reduce the temperature increase of the electronic device, allowing for higher powers to be achieved while maintaining a safe operating temperature. This paper reports on the use of silicon carbide (Sic) microchannels to dissipate high heat fluxes up to 1 kW/cm 2 over a footprint of 0.25 cm 2 . The use of high aspect ratio and decreased hydraulic diameter channels has allowed for very low thermal resistances to be achieved at higher heat duties compared to previous studies. The experiments performed resulted in heater temperatures of less than 60 °C and thermal resistances as low as 0.024 cm 2 . ° $C$/W between the heater surface and fluid inlet temperature. In conclusion, the demonstrated thermal performance of the SiC MCHS is an encouraging means for dissipating heat from high power density microelectronic devices.

42 ENGINEERING↗