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Results for “polycrystalline silicon”

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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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Microstructural and preliminary optical and microwave characterization of erbium-doped CaMoO 4 thin films

This work explores erbium-doped calcium molybdate (Er:CaMoO4) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the ∼1.5 μm Er 3+ 4f–4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction, and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO 4 formation that can be in situ doped with Er (typically 2–100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology, while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO 4 films. We perform preliminary optical and microwave characterization on the suspected Y 1 –Z 1 transition of 2 ppm, 200 nm epitaxial Er:CaMoO 4 annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.

Masiulionis, Ignas [Univ. of Chicago, IL (United S↗
DOE OSTI2020

Application of templated vapor-liquid-solid growth to heteroepitaxy of InP on Si

Direct growth of III–V semiconductors on Si promises to combine the superior optoelectronic properties of III–Vs with the existing large-scale fabrication capabilities for Si. Vapor-liquid-solid-based growth techniques have previously been used to grow optoelectronic-quality III–Vs in polycrystalline films and various photolithography-defined features. We show that templated vapor-liquid-solid growth can produce epitaxial material when performed on crystalline substrates. In templated vapor-liquid-solid growth, the metal group-III precursor is evaporated along with a capping SiO 2 layer on the crystalline substrate, then melted and converted with exposure to a vapor-phase group-V precursor. We demonstrate homoepitaxial growth of InP on InP wafers using two forms of the SiO x capping layer to confine the liquid metal: evaporated SiO 2 and solgel SiO x , the latter of which is necessary for growth on Si. We then demonstrate heteroepitaxial growth of InP islands on Si substrates from both evaporated and electroplated In metals. The templated vapor-liquid-solid process provides better material utilization and growth rates than common vapor-phase techniques, with similar control and convenience, providing a path toward the large-scale fabrication of integrated optoelectronic components.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Self-powered perovskite photon-counting detectors

Metal-halide perovskites (MHPs) have been successfully exploited for converting photons to charges or vice versa in applications of solar cells, light-emitting diodes and solar fuels for which all these applications involve strong light. Here we show that self-powered polycrystalline perovskite photodetectors can rival the commercial silicon photomultipliers (SiPMs) for photon counting. The photon-counting capability of perovskite photon-counting detectors (PCDs) is mainly determined by shallow traps, despite that deep traps also limit charge-collection efficiency. Two shallow traps with energy depth of 5.8 ± 0.8 millielectronvolts (meV) and 57.2 ± 0.1 meV are identified in polycrystalline methylammonium lead triiodide, which mainly stay at grain boundaries and the surface, respectively. We show that these shallow traps can be reduced by grain-size enhancement and surface passivation using diphenyl sulfide, respectively. It greatly suppresses dark count rate (DCR) from >20,000 counts per second per square millimetre (cps mm –2 ) to 2 cps mm –2 at room temperature, enabling much better response to weak light than SiPMs. The perovskite PCDs can collect γ-ray spectra with better energy resolution than SiPMs and maintain performance at high temperatures up to 85 °C. The zero-bias operation of perovskite detectors enables no drift of noise and detection property. Finally, this study opens a new application of photon counting for perovskites that uses their unique defect properties.

47 OTHER INSTRUMENTATION↗
NASA NTRS1995

Investigation of nucleation and growth processes of diamond films by atomic force microscopy

The nucleation and growth of plasma enhanced chemical vapor deposited (PECVD) polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for: (1) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (2) the silicon substrate-diamond film interface side of diamond films (1-4 micrometers thick) removed from the original surface of the substrate, and (3) cross-sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early-stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the films cross-section and interface however were not affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by small grained polycrystalline-like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X-ray photoelectron spectroscoy (XPS) spectra indicates that some silicon carbide is present in the precursor layer.

George, M. A.↗
DOE OSTI2025

Substrate effects on phase formation and interfacial stability in superconducting vanadium silicide thin films

Thin films of vanadium silicide (V-silicide) in the A15 cubic phase (V 3 Si) are promising for superconducting quantum devices due to their high transition temperature and potential compatibility with scalable semiconductor fabrication. However, solid-phase synthesis often yields secondary silicide phases that degrade performance. Here, in this study, we investigate the influence of substrate properties using two silicon-on-insulator architectures: one with a polycrystalline HfO 2 buried layer (group A) and the other with amorphous SiO 2 (group B). Both systems exhibit superconductivity consistent with V 3 Si formation, yet structural analysis reveals mixed-phase films in both cases. Crucially, only group A maintains an atomically sharp and chemically stable interface, a prerequisite for phase purity. Prolonged annealing in group A reduces the unwanted V 5 Si 3 phase but also leads to the emergence of Si-rich VSi 2 , likely due to localized substrate degradation. Preliminary atomic-resolution imaging suggests that HfO 2 crystallinity may promote local phase-selective nucleation. These findings highlight the importance of substrate design in promoting phase control and maintaining interfacial integrity in superconducting silicides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1994

Investigation of nucleation and growth processes of diamond films by atomic force microscopy

The nucleation and growth of plasma-enhanced chemical-vapor deposited polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for (1) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (2) the silicon substrate-diamond film interface side of diamond films (1-4 micrometers thick) removed from the original surface of the substrate, and (3) the cross-sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early-stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the film's cross section and interface, however, were not highly affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by a small grained polycrystalline-like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X-ray photoelectron spectroscopy spectra indicate that some silicon carbide is present in the precursor layer.

George, M. A.↗
NASA NTRS1972

Handbook of the optical, thermal and mechanical properties of six polycrystalline dielectric materials

The design data for six polycrystalline dielectric materials are presented to describe the optical, thermal, and mechanical properties. The materials are aluminum oxide, calcium fluoride, magnesium fluoride, magnesium oxide, silicon dioxide, and titanium dioxide. The primary interest is in the polycrystalline state, although single crystal data are included when appropriate. The temperature range is room temperature to melting point. The wavelength range is from near ultraviolet to near infrared.

Dewitt, D. P.↗
DOE OSTI2023

Nanopinhole Passivating Contact Si Solar Cells Fabricated with Metal-Assisted Chemical Etching

Monocrystalline Si (c-Si) solar cells with passivating contacts based on doped polycrystalline Si (poly-Si) on ≈2.0 nm silicon oxide (SiO x ) require >1000 °C thermal processing to create conducting pinholes in the SiO x layer. However, this high thermal budget can induce bulk defects in the Czochralski c-Si wafers used as the cell absorber layer. We demonstrate that pinholes can instead be created using metal-assisted chemical etching on planar or textured morphologies, at room temperature. This wet process creates up to 200 nm wide conducting pinholes that are directly observed with transmission electron and atomic force microscopies. High-performance hole-selective poly-Si/SiN y /SiO x and electron-selective poly-Si/SiO x passivating contacts are fabricated and implemented in laboratory-scale solar cells. This process development significantly broadens the range of passivation layer materials, their thicknesses, and surface morphologies, which enables the design of poly-Si contacts with superior passivating quality.

14 SOLAR ENERGY↗
DOE OSTI2021

Multimodal X-ray Microscopy: The Kinetics of Cu in CdTe Absorbers

The behavior of solar cells is very often limited by inhomogeneously distributed nanoscale defects. This is the case throughout the entire lifecycle of the solar cell, from the distribution of elements and defects during solar cell growth as well as the charge-collection and recombination during operation, to degradation and failure mechanisms due to impurity diffusion, crack formation, and irradiation- and heat-induced cell damage This has been known for a while in the field of crystalline silicon, but inhomogeneities are far more abundant in polycrystalline materials, and are the limiting factor in thin-film solar cells where grain sizes are often on the order of the diffusion length. We showed that the high penetration of hard X-rays combined with the high sensitivity to elemental distribution, structure, and spatial resolution offers a unique avenue for highly correlative studies at the nanoscale. We presented results on Cu-doped CdTe, where carrier collection is directly correlated to the kinetics of Cu inside the absorber and the particular Cu-phases at the ZnTe/CdTe interface. We complemented the results with modeling using PVRD-FASP and PyCDTS, where the X-ray beam induced profile can be reproduced by the equilibrium defect concentrations proposed by the solvers.

Bertoni, Mariana↗
NASA NTRS1979

Progress on the Dow Corning process for solar-grade silicon

The Dow Corning approach to increasing the resistivity of solar-grade silicon from about 0.04 ohm-cm (40 ppma B) to greater than 0.1 ohm-cm (10 ppma B) involves the use of high-purity raw materials carbothermically reduced in a specially designed electric arc furnace. Final purification occurs during Czochralski crystal growth of a polycrystalline ingot. This small-scale purification technology has resulted in silicon that has been fabricated into solar cells with a maximum AM1 conversion efficiency of 13.4%.

Hunt, L. P.↗
DOE OSTI2021

Trap-Assisted Dopant Compensation Prevents Shunting in Poly-Si Passivating Interdigitated Back Contact Silicon Solar Cells

Using a trap-assisted compensation model, we explain why polycrystalline Si (poly-Si) passivating contacts are able to achieve low leakage current between the doped fingers of interdigitated back contact (IBC) monocrystalline Si solar cells despite mixing of boron and phosphorus dopants in the isolation region. The fill factor of IBC solar cells is strongly affected by the electrical isolation region between n- and p-type fingers, as this region is critical in minimizing shunting losses. During fabrication of monocrystalline Si solar cells with poly-Si passivating contacts, the intrinsic poly-Si isolation region inevitably gets contaminated with both p- and n-type dopants. Using dopant profiles measured with time-of-flight secondary ion mass spectrometry and scanning probe measurements of the isolation region, we demonstrate that despite the dopant spreading during cell processing, a well-compensated region between the doped fingers exists that prevents shunting. The trap-assisted dopant compensation mechanism significantly widens the compensated region to tens of microns, where the residual dopant densities are below the trap density. This enables a high-resistivity region, resulting in low shunt current. Using one-dimensional (1-D) finite element diode simulations, we identify the design parameters and experimental conditions under which a sufficiently resistive region can form. Furthermore, our measurements of 2-D local resistivity and work function maps across the isolation region using scanning spreading resistance microscopy and Kelvin probe force microscopy demonstrate the existence of a highly resistive, wide compensated region and confirm our proposed compensation mechanism. For our structures, this region is ~25 µm in width within a ~150 µm wide finger isolation region with nearly 3 orders of magnitude higher resistivity than the regions dominated by a single type of dopant.

14 SOLAR ENERGY↗
NASA NTRS2005

Genesis Field Recovery

The Genesis mission returned to Earth on September 8, 2004 after a nearly flawless three-year mission to collect solar matter. The intent was to deploy a drogue chute and parafoil high over the Utah desert and to catch the fragile payload capsule in mid-air by helicopter. The capsule would then be opened in a clean-room constructed for that purpose at UTTR, and a nitrogen purge was to be installed before transporting the science canister to JSC. Unfortunately, both chutes failed to deploy, causing the capsule to fall to the desert floor at a speed of nearly 200 MPH. Still, Genesis represents a milestone in the US space program, comprising the first sample return since the Apollo Missions as well as the first return of materials exposed to the space environment outside of low Earth orbit and beyond the Earth s magnetosphere for an extended period. We have no other comparable materials in all of our collections on Earth. The goal of the Genesis Mission was to collect a representative sample of the composition of the solar wind and thus, the solar nebula from which our solar system originated. This was done by allowing the naturally accelerated species to implant shallowly in the surfaces of ultra-pure, ultra-clean collector materials. These collectors included single crystal silicon (FZ and CZ), sapphire, silicon carbide; those materials coated with aluminum, silicon, diamond like carbon, and gold; and isotopically enriched polycrystalline diamond and amorphous carbon. The majority of these materials were distributed on five collector arrays. Three of the materials were housed in an electrostatic concentrator designed to increase the flux of low-mass ions. There was also a two-inch diameter bulk metallic glass collector and a gold foil, polished aluminum, and molybdenum coated platinum foil collector. An excellent review of the Genesis collector materials is offered in reference [1].

McNamara, K. M.↗
NASA NTRS1989

Friction and wear of oxide-ceramic sliding against IN-718 nickel base alloy at 25 to 800 C in atmospheric air

The friction and wear of oxide-ceramics sliding against the nickel base alloy IN-718 at 25 to 800 C were measured. The oxide materials tested were mullite (3Al2O3.2SiO2); lithium aluminum silicate (LiAlSi(x)O(y)); polycrystalline monolithic alpha alumina (alpha-Al2O3); single crystal alpha-Al2O3 (sapphire); zirconia (ZrO2); and silicon carbide (SiC) whisker-reinforced Al2O3 composites. At 25 C the mullite and zirconia had the lowest friction and the polycrystalline monolithic alumina had the lowest wear. At 800 C the Al2O3-8 vol/percent SiC whisker composite had the lowest friction and the Al2O3-25 vol/percent SiC composite had the lowest wear. The friction of the Al2O3-SiC whisker composites increased with increased whisker content while the wear decreased. In general, the wear-resistance of the ceramics improve with their hardness.

Sliney, Harold E.↗
NASA NTRS1980

Fracture toughness of silicon

The paper presents a study to determine the fracture toughness and to characterize fracture modes of silicon as a function of the orientation of single-crystal and polycrystalline material. It is shown that bar specimens cracked by Knoop microhardness indentation and tested to fracture under four-point bending at room temperature were used to determine the fracture toughness values. It is found that the lowest fracture toughness value of single crystal silicon was 0.82 MN/m to the 3/2 in the 111 plane type orientation, although the difference in values in the 111, 110, and 100 planes was small.

Chen, C. P.↗
NASA NTRS1991

Selective and low temperature synthesis of polycrystalline diamond

Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

Ramesham, R.↗
NASA NTRS2009

Status of Reconstruction of Fragmented Diamond-on-Silicon Collector From Genesis Spacecraft Solar Wind Concentrator

In addition to passive solar wind collector surfaces, the Genesis Discovery Mission science canister had on board an electrostatic concave mirror for concentrating the solar wind ions, known as the concentrator . The 30-mm-radius collector focal point (the target) was comprised of 4 quadrants: two of single crystal SiC, one of polycrystalline 13C diamond and one of diamond-like-carbon (DLC) on a silicon substrate. [DLC-on-silicon is also sometimes referenced as Diamond-on-silicon, DOS.] Three of target quadrants survived the hard landing intact, but the DLC-on-silicon quadrant fractured into numerous pieces (Fig. 1). This abstract reports the status of identifying the DLC target fragments and reconstructing their original orientation.

Rodriquez, Melissa C.↗
NASA NTRS1991

Flexible copper-indium-diselenide films and devices for space applications

With the ever increasing demands on space power systems, it is imperative that low cost, lightweight, reliable photovoltaics be developed. One avenue of pursuit for future space power applications is the use of low cost, lightweight flexible PV cells and arrays. Most work in this area assumes the use of flexible amorphous silicon (a-Si), despite its inherent instability and low efficiencies. However, polycrystalline thin film PV such as copper-indium-diselenide (CIS) are inherently more stable and exhibit better performance than a-Si. Furthermore, preliminary data indicate that CIS also offers exciting properties with respect to space applications. However, CIS has only heretofore only produced on rigid substrates. The implications of flexible CIS upon present and future space power platforms was explored. Results indicate that space qualified CIS can dramatically reduce the cost of PV, and in most cases, can be substituted for silicon (Si) based on end-of-life (EOL) estimations. Furthermore, where cost is a prime consideration, CIS can become cost effective than gallium arsenide (GaAs) in some applications. Second, investigations into thin film deposition on flexible substrates were made, and data from these tests indicate that fabrication of flexible CIS devices is feasible. Finally, data is also presented on preliminary TCO/CdS/CuInSe2/Mo devices.

Armstrong, J. H.↗