Search NASA⌕ Search

SEARCH · Search NASA

Results for “electron doping”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Probing the Structures and Electronic Properties of Dual-Phosphorus-Doped Gold Cluster Anions (AunP-2, n = 1–8): A Density functional Theory Investigation

The geometries of gold clusters doped with two phosphorus atoms, (AunP-2, n = 1–8) were investigated using density functional theory (DFT) methods. Various two-dimensional (2D) and three-dimensional (3D) structures of the doped clusters were studied. The results indicate that the structures of dual-phosphorus-doped gold clusters exhibit large differences from those of pure gold clusters with small cluster sizes. In our study, as for Au6P-2, two cis–trans isomers were found. The global minimum of Au8P-2 presents a similar configuration to that of Au-20, a pyramid-shaped unit, and the potential novel optical and catalytic properties of this structure warrant further attention. The higher stability of AunP-2 clusters relative to Au-n+2 (n = 1–8) clusters was verified based on various energy parameters, and the results indicate that the phosphorus atom can improve the stabilities of the gold clusters. We then explored the evolutionary path of (n = 1–8) clusters. We found that AunP-2 clusters exhibit the 2D–3D structural transition at n = 6, which is much clearer and faster than that of pure gold clusters and single-phosphorus-doped clusters. The electronic properties of AunP-2 (n = 1–8) were then investigated. The photoelectron spectra provide additional fundamental information on the structures and molecular orbitals shed light on the evolution of AunP-2 (n = 1–8). Natural bond orbital (NBO) described the charge distribution in stabilizing structures and revealed the strong relativistic effects of the gold atoms.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

Structural, electronic and magnetic properties of carbon doped boron nitride nanowire: Ab initio study

Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior such as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is more stable than the other positions of carbon impurity. Our calculations show that C-doped BNNW may offer unique opportunities for developing nanoscale spintronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electronic structure of boron and aluminum δ -doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum δ-doped layers in silicon with densities above the solid solubility limit. For this study, we use density functional theory to predict the band structure and effective mass values of such δ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the δ layers is found to lead to a significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these δ-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor δ-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine-tuned.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Hot-electron energy relaxation time in Ga-doped ZnO films

Hot-electron energy relaxation time is deduced for Ga-doped ZnO epitaxial layers from pulsed hot-electron noise measurements at room temperature. The relaxation time increases from ∼0.17 ps to ∼1.8 ps when the electron density increases from 1.4 × 10{sup 17 }cm{sup −3} to 1.3 × 10{sup 20 }cm{sup −3}. A local minimum is resolved near an electron density of 1.4 × 10{sup 19 }cm{sup −3}. The longest energy relaxation time (1.8 ps), observed at the highest electron density, is in good agreement with the published values obtained by optical time-resolved luminescence and absorption experiments. Monte Carlo simulations provide a qualitative interpretation of our observations if hot-phonon accumulation is taken into account. The local minimum of the electron energy relaxation time is explained by the ultrafast plasmon-assisted decay of hot phonons in the vicinity of the plasmon–LO-phonon resonance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2008

Nano-Multiplication-Region Avalanche Photodiodes and Arrays

Nano-multiplication-region avalanche photodiodes (NAPDs), and imaging arrays of NAPDs integrated with complementary metal oxide/semiconductor (CMOS) active-pixel-sensor integrated circuitry, are being developed for applications in which there are requirements for high-sensitivity (including photoncounting) detection and imaging at wavelengths from about 250 to 950 nm. With respect to sensitivity and to such other characteristics as speed, geometric array format, radiation hardness, power demand of associated circuitry, size, weight, and robustness, NAPDs and arrays thereof are expected to be superior to prior photodetectors and arrays including CMOS active-pixel sensors (APSs), charge-coupled devices (CCDs), traditional APDs, and microchannelplate/ CCD combinations. Figure 1 depicts a conceptual NAPD array, integrated with APS circuitry, fabricated on a thick silicon-on-insulator wafer (SOI). Figure 2 presents selected aspects of the structure of a typical single pixel, which would include a metal oxide/semiconductor field-effect transistor (MOSFET) integrated with the NAPD. The NAPDs would reside in silicon islands formed on the buried oxide (BOX) layer of the SOI wafer. The silicon islands would be surrounded by oxide-filled insulation trenches, which, together with the BOX layer, would constitute an oxide embedding structure. There would be two kinds of silicon islands: NAPD islands for the NAPDs and MOSFET islands for in-pixel and global CMOS circuits. Typically, the silicon islands would be made between 5 and 10 m thick, but, if necessary, the thickness could be chosen outside this range. The side walls of the silicon islands would be heavily doped with electron-acceptor impurities (p+-doped) to form anodes for the photodiodes and guard layers for the MOSFETs. A nanoscale reach-through structure at the front (top in the figures) central position of each NAPD island would contain the APD multiplication region. Typically, the reach-through structure would be about 0.1 microns in diameter and between 0.3 and 0.4 nm high. The top layer in the reach-through structure would be heavily doped with electron-donor impurities (n+-doped) to make it act as a cathode. A layer beneath the cathode, between 0.1 and 0.2 nm thick, would be p-doped to a concentration .10(exp 17)cu cm. A thin n+-doped polysilicon pad would be formed on the top of the cathode to protect the cathode against erosion during a metal-silicon alloying step that would be part of the process of fabricating the array.

Zheng, Xinyu↗
DOE OSTI2013

Establishment of the correlation law between electron density, infrared absorption and doping concentration in Ga{sup 3+}-doped ZnO

Highlights: ► Synthesis of nanometric A{sup 3+}-doped ZnO by polyol-mediated route. ► Correlation between free electron density and the doping rate of A{sup 3+}-doped ZnO. ► Optimization of infrared absorbing properties of A{sup 3+}-doped ZnO. - Abstract: A polyol-mediated synthesis allows the obtaining of doped zinc oxides nanoparticles with tunable infrared absorption properties via the doping concentration. In a first step the prepared nanoparticles are characterized in terms of chemical composition (purity and homogeneity), crystallite size and agglomerate morphology. A correlation law between the infrared absorbing efficiency, the free electron density and the doping concentration is then clearly established; this law is based on the neighboring probability of the dopant ions in the crystal network.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electronic and magnetic properties of Mo doped graphene; full potential approach

The electronic and magnetic properties of Pristine and Mo doped Graphene have been calculated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method based on Density Functional Theory (DFT). The exchange and correlation (XC) effects were taken into account by generalized gradient approximation (GGA). The calculated results show that Mo doping creates magnetism in Graphene by shifting the energy levels at E{sub F} and opens up a channel for Graphene to be used in real nanoscale device applications. The unpaired d-electrons of Mo atom are responsible for induced magnetism in Graphene. Magnetic ordering created in Graphene in this way makes it suitable for recording media, magnetic sensors, magnetic inks and spintronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Electronic Structure of Tungsten-Doped β -Ga 2 O 3 Compounds

Tungsten (W) doped gallium oxide (Ga2O3) (Ga2-2xWxO3, 0.00=x=0.30, GWO) polycrystalline ceramic compounds were synthesized via conventional, high-temperature solid-state reaction method. The effect of W-doping on the crystal structure and electronic structure of the resulting GWO materials is studied in detail. The GWO compounds were single-phase, crystallized in ß-Ga2O3 for x=0.15, at which point the Ga2O3-WO3 composite formation occurs. The average crystallite size increases with increasing W-content; however, the effect is predominant only in the single phase GWO compounds. Corroborating with structural analyses, the X-ray photoelectron spectroscopy (XPS) measurements reveal the chemical state of W ions vary in GWO compounds as a function of W concentration. The mixed chemical valence states of W (W4+ and W6+) were evident in single-phase GWO compounds where the W-concentration is lower. However, W ions exhibit the highest chemical valence state (W6+) for higher x values, which resulted in the Ga2O3-WO3 composite formation. The Ga ions exists in their highest chemical valence state (Ga3+) in all of the GWO compounds. The scientific understanding of the electronic structure of the GWO materials derived as function of W concentration could be useful while considering the W-doped Ga2O3 materials and/or W-Ga2O3 contacts for electronic and optoelectronic device applications.

W-doping, Ga2O3-WO3 Composite, Electronic Structur↗
DOE OSTI2014

Structural and electronic properties of LaO δ-doped SrTiO₃ caused by biaxial strain

δ-doping in SrTiO₃ plays a pivotal role for oxide electronics. By first-principles density functional calculations, we reveal that the electronic and structural properties of LaO δ-doped SrTiO₃ can be drastically altered by compressive biaxial inplane strains. We predict the existence of a critical inplane strain (η c ) above which many interesting phenomena occur, including (i) a profound symmetry breaking to the doping-induced electron states, (ii) a dramatic decline of the electron potential over a short distance of 2.5 Å near the doping layer, (iii) a new structure pattern of cation-anion displacements, and (iv) the emergence of unusual downward dispersions in the conduction bands with negative effective masses for electrons. The microscopic insight for these interesting phenomena is provided. Our study demonstrates that biaxial inplane strain can effectively modify the electronic properties in δ-doped SrTiO₃ for the purpose of oxide electronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1986

Characterization of the heavily doped emitter and junction regions of silicon solar cells using an electron beam

Heavily doped emitter and junction regions of silicon solar cells are investigated by means of the electron-beam-induced-current (EBIC) technique. Although the experimental EBIC data are collected under three-dimensional conditions, it is analytically demonstrated with two numerical examples that the solutions obtained with one-dimensional numerical modeling are adequate. EBIC data for bare and oxide-covered emitter surfaces are compared with theory. The improvement in collection efficiency when an emitter surface is covered with a 100-A SiO2 film varies with beam energy; for a cell with a junction depth of 0.35 microns, the improvement is about 54 percent at 2 keV.

Luke, K. L.↗
DOE OSTI2018

Lewis Acid Doping Induced Synergistic Effects on Electronic and Morphological Structure for Donor and Acceptor in Polymer Solar Cells

Abstract Due to the attraction of optimizing the electronic structure beyond chemical synthesis, molecular doping has recently aroused wide interest in the field of organic solar cells. However, the selection of limited dopants confines its successful application. Inspired by the Lewis base characteristics of the photovoltaic materials, the Lewis acid as novel dopant is introduced in organic solar cells. In both fullerene and nonfullerene based blends, Lewis acid doping leads to increased photovoltaic performance. Detailed experiments reveal that Lewis acid doping has a synergistic effect on modifying the polymer's electronic properties and the acceptor's nanostructure even at low doping concentration, and these are simultaneously responsible for the device improvements. Based on the mechanism studies, it is proposed that the Lewis acid‐doped polymers anions produce induced dipole on the acceptor, this increases the intermolecular interaction and facilitates the morphology optimization. It is believed that the synergistic effect by Lewis acid doping greatly expands the application of doped organic solar cells, in concert with other existing methods to yield higher efficiency values.

Yan, Han↗
DOE OSTI2014

A novel approach to prepare optically active ion doped luminescent materials via electron beam evaporation into ionic liquids

A novel approach to prepare luminescent materials via electron-beam evaporation into ionic liquids is presented which even allows doping of host lattices with ions that have a strong size mismatch. Thus, to prove this, MgF 2 nanoparticles doped with Eu 3+ were fabricated. The obtained nanoparticles featured an unusually high luminescence lifetime and the obtained material showed a high potential for application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

10 MeV electrons irradiation effects in variously doped n-GaN

We studied 10 MeV electron irradiation effects in a group of n-GaN films grown by standard metalorganic chemical vapor deposition (MOCVD) and by epitaxial lateral overgrowth (ELOG) techniques. The samples were either undoped or Si-doped, so that the shallow donor concentrations ranged from 10{sup 14} cm{sup -3} to 3 x 10{sup 18} cm{sup -3}. It was found that electron irradiation led to the compensation of n-type conductivity and that the carrier removal rate substantially increased with an increase in the starting donor concentration. For the MOCVD samples, it was observed that the main compensating defect introduced by electrons was a 0.15 eV electron trap detected by admittance spectroscopy. Once the Fermi level crossed the level of these traps two other centers with activation energies of 0.2 and 1 eV were found to contribute to the compensation, so that after high doses, the Fermi level in moderately doped samples was pinned near E{sub c}-1 eV. In ELOG samples the 0.15 eV electron traps were not detected. Instead only the 0.2 and 1 eV traps were introduced by irradiation. The carrier removal rate in the ELOG n-GaN was found to be measurably lower than for MOCVD samples with a similar doping level. The results are compared to previously published data and possible models of compensation are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Hydrogen adsorption and anomalous electronic properties of nitrogen-doped graphene

We investigate hydrogen adsorption effects on stabilities and electronic properties of nitrogen defects in graphene using first-principles electronic-structure calculations within the density-functional theory. We find that the adsorption of hydrogen atoms on the pyridine-type nitrogen defects in graphene becomes energetically favorable, whereas in the case of the substitutional nitrogen defect the hydrogen adsorption becomes unfavorable. We also find that a transition from p-type to n-type doping properties occurs by hydrogen adsorption on the pyridine-type defects, suggesting that even the carrier type is controllable in nitrogen-doped graphene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Doping Induced Magnetic and Electronic Phase Transitions in the Ferrimagnetic Half-Metallic Mn 4 Al 11 Compound

The future of spintronics and semiconductor applications demands materials with tailored electronic and magnetic properties. Here, this study uses density functional theory to investigate the electronic structure of the half-metallic compound Mn 4 Al 11 under uniaxial strain and in its Ge-substituted derivatives. Strain analysis shows that although the half-metallic band gap collapses under strain beyond −2%, the ferrimagnetic character remains stable. Ge substitution at six inequivalent Al sites in Mn 4 Al 11 results in varying degrees of metallicity and magnetic properties. Substitution at Al═ (000) induces a metal-to-insulator transition with an indirect semiconducting gap of 0.14 eV. Bonding and hybridization analyses reveal that local Mn–Al interactions due to Ge substitution significantly modify the local electronic structure, causing both electronic and magnetic phase transitions. This work highlights the effectiveness of substitutional doping in tuning half-metallicity and magnetic properties in inorganic solids, enabling the design of materials for future technological applications.

alloys↗
DOE OSTI2025

Co‐Doping Approach for Enhanced Electron Extraction to TiO 2 for Stable Inorganic Perovskite Solar Cells

Inorganic perovskite CsPbI 3 solar cells hold great potential for improving the operational stability of perovskite photovoltaics. However, electron extraction is limited by the low conductivity of TiO 2 , representing a bottleneck for achieving stable performance. In this study, a co‐doping strategy for TiO 2 using Nb(V) and Sn(IV), which reduces the material's work function by 80 meV compared to Nb(V) mono‐doped TiO 2 , is introduced. To gain fundamental understanding of the processes at the interfaces between the perovskite and charge‐selective layer, transient surface photovoltage measurements are applied, revealing the beneficial effect of the energetic and structural modification on electron extraction across the CsPbI 3 /TiO 2 interface. Using 2D drift‐diffusion simulations, it is found that co‐doping reduces the interface hole recombination velocity by two orders of magnitude, increasing the concentration of extracted electrons by 20%. When integrated into n–i–p solar cells, co‐doped TiO 2 enhances the projected T S80 lifetimes under continuous AM1.5G illumination by a factor of 25 compared to mono‐doped TiO 2 . This study provides fundamental insights into interfacial charge extraction and its correlation with operational stability of perovskite solar cells, offering potential applications for other charge‐selective contacts.

14 SOLAR ENERGY↗