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At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS2006

SiC Field Effect Transistor Technology Demonstrating Prolonged Stable Operation at 500 C

While there have been numerous reports of short-term transistor operation at 500 degree C or above, these devices have previously not demonstrated sufficient long-term operational durability at 500 degree C to be considered viable for most envisioned applications. This paper reports the development of Silicone Carbi field effect transistors capable of long-term electrical operation at 500 degree C. A 6H-SiC MESFET was packaged and subjected to continuous electrical operation while residing in a 500 degree C oven in oxidizing air atmosphere for over 2400 hours. The transistor gain, saturation current (IDSS), and on-resistance (RDS) changed by less than 20% from initial values throughout the duration of the biased 500 degree C test. Another high-temperature packaged 6H-SiC MESFET was employed to form a simple one-stage high-temperature low-frequency voltage amplifier. This single-stage common-source amplifier demonstrated stable continuous electrical operation (negligible changes to gain and operating biases) for over 600 hours while residing in a 500 degree C air ambient oven. In both cases, increased leakage from annealing of the Schottky gate-to-channel diode was the dominant transistor degradation mechanism that limited the duration of 500 degree C electrical operation.

Neudeck, Philip G.↗

DOE OSTI2020

Electrical injection and transport in Teflon-diluted hole transport materials

Diluting small molecule organic semiconductor hole transport materials with Teflon AF (TAF) dramatically increases their thermal/morphological stability while counterintuitively also increasing the current density in hole-only diodes. Here, we explore the origin of this current enhancement in co-evaporated blends of TAF and N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD) and find that it results from improved hole injection and not from a mobility enhancement due to semiconductor dilution effects. Whereas electroabsorption measurements indicate that an interface dipole shift of up to 0.5 eV (depending on TAF concentration) aides hole injection at the indium-tin-oxide anode, time-of-flight and temperature-dependent current-voltage measurements show that the mobility of 25 vol% TAF:NPD blends decreases by roughly an order of magnitude relative to neat NPD despite having slightly lower energetic disorder. For comparison, diluting with 25 vol% high density polyethylene achieves a similar reduction in energetic disorder but only decreases the mobility by a factor of two. Furthermore, these results highlight the tradeoff between reducing energetic disorder and frustrating percolation in diluted organic semiconductors, and represent a step toward thermally-evaporated polymer-small molecule composites that maintain high mobility while offering improved morphological stability and lower refractive index for organic light emitting diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Top-Performing Photovoltaic Cells Compared to the Shockley–Queisser Limit

Top-performing single-junction and two-terminal tandem devices that include at least one polycrystalline cell are compared with each other and their ideal limits. The parameters of open-circuit voltage, short-circuit current, and fill-factor are individually compared to the Shockley–Queisser limit to investigate where different technologies have room to improve. Technologies, such as silicon and cadmium telluride have the most room for improvement in open-circuit voltage currently utilizing 87% and 81% of their maxima, respectively. Detailed diode and fill-factor loss analysis is presented for single-junction devices to give further insight on how they compare and where efficiency is lost. Single-crystal technologies demonstrate a fill-factor closer to the Shockley–Queisser limit than polycrystalline devices. The high diode quality factor of polycrystalline devices is the leading cause of the decreased fill-factor. Similar analysis on tandem cells with at least one thin-film cell shows that although their efficiency exceeds that of the single-junction cells, the fraction of their ideal efficiency is smaller. Here, by comparing parameters to the Shockley–Queisser limit, it becomes clearer where certain technologies have the potential for improvement.

High efficiency↗

DOE OSTI2023

Sensitive and robust thin film X-ray detector using 2D layered perovskite diodes

A radiation detector includes a p-i-n architecture including a p-type contact layer, an n-type contact layer, and an intrinsic layer between the p-type contact layer and the n-type contact layer. The intrinsic layer includes a thin film comprising a highly crystalline 2D layered perovskite material. The radiation detectors according to embodiments of the present disclosure generate high open circuit voltages, have good detecting photon density limits and high sensitivities, and can be self-powered.

Tsai, Hsinhan↗

NASA NTRS2010

Solar cell circuit and method for manufacturing solar cells

The invention is a novel manufacturing method for making multi-junction solar cell circuits that addresses current problems associated with such circuits by allowing the formation of integral diodes in the cells and allows for a large number of circuits to readily be placed on a single silicon wafer substrate. The standard Ge wafer used as the base for multi-junction solar cells is replaced with a thinner layer of Ge or a II-V semiconductor material on a silicon/silicon dioxide substrate. This allows high-voltage cells with multiple multi-junction circuits to be manufactured on a single wafer, resulting in less array assembly mass and simplified power management.

Mardesich, Nick↗

DOE OSTI2020

A sensitive and robust thin-film x-ray detector using 2D layered perovskite diodes

Solid-state radiation detectors, using crystalline semiconductors to convert radiation photons to electrical charges, outperform other technologies with high detectivity and sensitivity. Here, we demonstrate a thin-film x-ray detector comprised with highly crystalline two-dimensional Ruddlesden-Popper phase layered perovskites fabricated in a fully depleted p-i-n architecture. It shows high diode resistivity of 10 12 ohm·cm in reverse-bias regime leading to a high x-ray detecting sensitivity up to 0.276 C Gy air –1 cm –3 . Such high signal is collected by the built-in potential underpinning operation of primary photocurrent device with robust operation. The detectors generate substantial x-ray photon–induced open-circuit voltages that offer an alternative detecting mechanism. Furthermore, our findings suggest a new generation of x-ray detectors based on low-cost layered perovskite thin films for future x-ray imaging technologies.

47 OTHER INSTRUMENTATION↗

NASA NTRS1984

Space-charge behavior of 'Thin-MOS' diodes with MBE-grown silicon films

Basic theoretical and experimental characteristics of a novel 'Thin-MOS' technology, which has promising aspects for integrated high-frequency devices up to several hundred gigahertz are presented. The operation of such devices depends on charge injection into undoped silicon layers of about 1000-A thickness, grown by molecular beam epitaxy on heavily doped substrates, and isolation by thermally grown oxides of about 100-A thickness. Capacitance-voltage characteristics measured at high and low frequencies agree well with theoretical ones derived from uni and ambipolar space-charge models. It is concluded that after oxidation the residual doping in the epilayer is less than approximately 10 to the 16th/cu cm and rises by 3 orders of magnitude at the substrate interface within less than 100 A and that interface states at the oxide interface can be kept low.

Lieneweg, U.↗

NASA NTRS2007

324GHz CMOS VCO Using Linear Superimposition Technique

Terahertz (frequencies ranged from 300GHz to 3THz) imaging and spectroscopic systems have drawn increasing attention recently due to their unique capabilities in detecting and possibly analyzing concealed objects. The generation of terahertz signals is nonetheless nontrivial and traditionally accomplished by using either free-electron radiation, optical lasers, Gunn diodes or fundamental oscillation by using III-V based HBT/HEMT technology[1-3]... We have substantially extended the operation range of deep-scaled CMOS by using a linear superimposition method, in which we have realized a 324GHz VCO in 90nm digital CMOS with 4GHz tuning range under 1V supply voltage. This may also pave the way for ultra-high data rate wireless communications beyond that of IEEE 802.15.3c and reach data rates comparable to that of fiber optical communications, such as OC768 (40Gbps) and beyond.

voltage controlled oscillators (VCO)↗

DOE OSTI2023

Implanted Guard Ring Edge Termination With Avalanche Capability for Vertical GaN Devices

Edge termination is the key building block in power devices to enable near-ideal, avalanche breakdown voltage (BV). Here, this work presents the design, fabrication, and physics of a GaN guard ring (GR) edge termination formed by selective-area nitrogen implantation through an epitaxial p-GaN layer. The fabrication of this termination only includes a single implantation step that does not require precise control of implant depth, rendering a large process latitude. The selective-area implantation produces p-GaN rings that are separated by the implanted, semi-insulating regions. The number and spacing of the p-type rings are found to determine the BV of the vertical GaN p-n diode. The 16-ring structure enables a BV of 1800 V, being 88% of the theoretical 1-D parallel-plane limit. Avalanche characteristics are observed in devices with a large variety of GR designs. Finally, we present a comprehensive survey on the efficiency, fabrication complexity, real estate, and avalanche capability of various edge termination techniques that have been reported in vertical GaN devices. The high efficiency (among the highest reported in avalanche-capable GaN terminations), simple and robust fabrication process, and uniform avalanche capability make this implanted GR a promising edge termination for high-voltage GaN devices.

42 ENGINEERING↗

NASA NTRS2013

Narrow Line X-Ray Calibration Source for High Resolution Microcalorimeters

We are developing a narrow line calibration source for use with X-ray microcalorimeters. At energies below 300 electronvolts fluorescent lines are intrinsically broad, making calibration of high resolution detectors difficult. This source consists of a 405 nanometers (3 electronvolts) laser diode coupled to an optical fiber. The diode is pulsed to create approximately one hundred photons in a few microseconds. If the pulses are short compared to the rise time of the detector, they will be detected as single events with a total energy in the soft X-ray range. Poisson fluctuations in photon number per pulse create a comb of X-ray lines with 3 electronvolts spacing, so detectors with energy resolution better than 2 electronvolts are required to resolve the individual lines. Our currently unstabilized diode has a multimode width less than 1 nanometer, giving a 300 electronvolt event a Full width at half maximum (FWHM) less than 0.1 electronvolts. By varying the driving voltage, or pulse width, the source can produce a comb centered on a wide range of energies. The calibration events are produced at precisely known times. This allows continuous calibration of a flight mission without contaminating the observed spectrum and with minimal deadtime.

high resolution detectors↗

NASA NTRS1973

Effects of nuclear radiation on a high-reliability silicon power diode. 4: Analysis of reverse bias characteristics

The effects of nuclear radiation on the reverse bias electrical characteristics of one hundred silicon power diodes were investigated. On a percentage basis, the changes in reverse currents were large but, due to very low initial values, this electrical characteristic was not the limiting factor in use of these diodes. These changes were interpreted in terms of decreasing minority carrier lifetimes as related to generation-recombination currents. The magnitudes of reverse voltage breakdown were unaffected by irradiation.

Been, J. F.↗

NASA NTRS1983

Thin wire pointing method

A method is described for forming sharp tips on thin wires, in particular phosphor bronze wires of diameters such as one-thousandth inch used to contact micron size Schottky barrier diodes, which enables close control of tip shape and which avoids the use of highly toxic solutions. The method includes dipping an end of a phosphor bronze wire into a dilute solution of sulfamic acid and applying a current through the wire to electrochemically etch it. The humidity in the room is controlled to a level of less than 50%, and the voltage applied between the wire and another electrode in the solutions is a half wave rectified voltage. The current through the wire is monitored, and the process is stopped when the current falls to a predetermined low level.

Green, G.↗

NASA NTRS1975

Effects of processing on the carrier lifetime in silicon solar cells

Measurements were taken to determine the effects that solar cell processing steps have on the minority carrier lifetime in silicon. The experimental work included measurements of diffusion lengths of the silicon at various stages of cell fabrication, of solar cell properties, and of the PN junction properties for ingots covering a wide range of doping and other ingot properties. Resistivities covered the range of 0.01 to 10 ohm-cm, and combinations of extreme concentrations (high and low) of dislocations and oxygen were included. The results showed that the major cell process steps did not usually cause any appreciable change in diffusion lengths. The solar cell currents obtained supported the diffusion length measurements. The effects of heavy doping concentrations on solar cell performance were studied. Attempts were made to relate the voltage behavior of the cells with the diode properties and the properties of the ingots.

Iles, P. A.↗

NASA NTRS1991

High-power converters for space applications

Phase 1 was a concept definition effort to extend space-type dc/dc converter technology to the megawatt level with a weight of less than 0.1 kg/kW (220 lb./MW). Two system designs were evaluated in Phase 1. Each design operates from a 5 kV stacked fuel cell source and provides a voltage step-up to 100 kV at 10 A for charging capacitors (100 pps at a duty cycle of 17 min on, 17 min off). Both designs use an MCT-based, full-bridge inverter, gaseous hydrogen cooling, and crowbar fault protection. The GE-CRD system uses an advanced high-voltage transformer/rectifier filter is series with a resonant tank circuit, driven by an inverter operating at 20 to 50 kHz. Output voltage is controlled through frequency and phase shift control. Fast transient response and stability is ensured via optimal control. Super-resonant operation employing MCTs provides the advantages of lossless snubbing, no turn-on switching loss, use of medium-speed diodes, and intrinsic current limiting under load-fault conditions. Estimated weight of the GE-CRD system is 88 kg (1.5 cu ft.). Efficiency of 94.4 percent and total system loss is 55.711 kW operating at 1 MW load power. The Maxwell system is based on a resonance transformer approach using a cascade of five LC resonant sections at 100 kHz. The 5 kV bus is converted to a square wave, stepped-up to a 100 kV sine wave by the LC sections, rectified, and filtered. Output voltage is controlled with a special series regulator circuit. Estimated weight of the Maxwell system is 83.8 kg (4.0 cu ft.). Efficiency is 87.2 percent and total system loss is 146.411 kW operating at 1 MW load power.

Park, J. N.↗

DOE OSTI2021

Demonstration of a Three-Dimensionally Structured Betavoltaic

In this work, we present a demonstration of a high-aspect ratio, three-dimensionally structured betavoltaic device. High-aspect ratio silicon PIN diodes were used as the semiconductor absorber and 147 PmCl 3 was used as the beta emitter. Three devices were fabricated with 147 Pm activities of 2.4 mCi, 7.4 mCi, and 29.5 mCi. The device with the highest activity produced an initial power output of 200 nW and was monitored over a period of 8 months to observe the current–voltage behavior over time, during which time the output current decreased in accordance with the radioactive half-life of 147 Pm. Small deviations in the output current of a few percent during the long-term measurement were found to be attributable to the humidity in the room where the experiment was done. Furthermore, the output current generated from the devices was 68–77% of the theoretical maximum, indicating significant infiltration of the radioisotope into the ridged structures.

42 ENGINEERING↗

DOE OSTI2024

A method to observe field-region oxide charge and inter-electrode isolation from CV-characteristics of n-on-p devices

Abstract N-on-psilicon sensors will be utilized in the Compact Muon Solenoid (CMS) detector's tracker and High Granularity Calorimeter (HGCAL) in the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). Among their several advantages in terms of radiation hardness over the traditionalp-on-nsensors in the extreme radiation environment of the HL-LHC are electron collection instead of holes and overlapping maxima of weighting and electric fields at the charge-collecting electrodes. The disadvantage of the multi-channel SiO 2 -passivatedn-on-psensors is the generation of an inversion layer under the Si/SiO 2 -interface by a positive interface-oxide-charge (N ox ) that at high densities can compromise the position resolution by creating a conduction channel between the electrodes. This issue is typically addressed by including additional isolnts (p-stp,p-spray) between n + -electrodes. Focusing on the guard-ring regions ofn-on-psensors where no isolation implants are applied between the electrodes, a capacitance-voltage (CV) characterization study of both 6-inch wafer test diodes and 8-inch HGCAL prototype and pre-series sensors showed a distinct threshold voltage (V th,iso ) in theCV-characteristics of a biased n + -electrode when its enclosing guard-ring was left floating. When reproduced by simulations, the measuredV th,iso was found to contain information on the field-regionN ox and indicate the threshold where the two electrodes become electrically isolated by the influence of the reverse bias voltage. Together with previous studies on the inter-electrode isolation of irradiatedn-on-psensors, the results indicate that position sensitiven-on-psensors without isolation implants may be feasible in future HEP experiments.

Instruments & Instrumentation↗

DOE OSTI2020

Structural and spectral dynamics of single-crystalline Ruddlesden-Popper phase halide perovskite blue light-emitting diodes

Achieving perovskite-based high–color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high–color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr 6 ] 4- octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission.

36 MATERIALS SCIENCE↗

NASA NTRS1982

A new strategy for efficient solar energy conversion: Parallel-processing with surface plasmons

This paper introduces an advanced concept for direct conversion of sunlight to electricity, which aims at high efficiency by tailoring the conversion process to separate energy bands within the broad solar spectrum. The objective is to obtain a high level of spectrum-splitting without sequential losses or unique materials for each frequency band. In this concept, sunlight excites a spectrum of surface plasma waves which are processed in parallel on the same metal film. The surface plasmons transport energy to an array of metal-barrier-semiconductor diodes, where energy is extracted by inelastic tunneling. Diodes are tuned to different frequency bands by selecting the operating voltage and geometry, but all diodes share the same materials.

Anderson, L. M.↗