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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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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Quasi-Static Time Series Fatigue Simulation for PV Inverter Semiconductors with Long-Term Solar Profile

Power system simulations with long-term data tend to have large time steps varying from one second to a few minutes. However, for PV inverter semiconductors, the minimum thermal stresses cycle is with line frequency. This requires the time step of the fatigue simulation to be much smaller than the line period. This small time step results in poor simulation speed, especially for long-term simulations. This paper proposes a fast fatigue simulation for inverter semiconductors using the quasi-static time series (QSTS) simulation concept. The fatigue analysis typically focuses on the peak and valley values of a strain and neglect the transients from peaks to valleys. The proposed simulation utilizes this property of fatigue analysis and calculates the steady state of the semiconductor junction temperature only. The resulting time step of the fatigue simulation is 15 minutes, which is consistent with the solar dataset without losing accuracy.

fast simulation↗
DOE OSTI2022

Reconfiguring band-edge states and charge distribution of organic semiconductor–incorporated 2D perovskites via pressure gating

Two-dimensional (2D) semiconductor heterostructures are key building blocks for many electronic and optoelectronic devices. Reconfiguring the band-edge states and modulating their interplay with charge carriers at the interface in a continuous manner have long been sought yet are challenging. Here, using organic semiconductor–incorporated 2D halide perovskites as the model system, we realize the manipulation of band-edge states and charge distribution via mechanical—rather than chemical or thermal—regulation. Compression induces band-alignment switching and charge redistribution due to the different pressure responses of organic and inorganic building blocks, giving controllable emission properties of 2D perovskites. We propose and demonstrate a “pressure gating” strategy that enables the control of multiple emission states within a single material. We also reveal that band-alignment transition at the organic-inorganic interface is intrinsically not well resolved at room temperature owing to the thermally activated transfer and shuffling of band-edge carriers. This work provides important fundamental insights into the energetics and carrier dynamics of hybrid semiconductor heterostructures.

42 ENGINEERING↗
DOE OSTI2024

Anomalous isotope effect on the optical bandgap in a monolayer transition metal dichalcogenide semiconductor

Isotope effects have received increasing attention in materials science and engineering because altering isotopes directly affects phonons, which can affect both thermal properties and optoelectronic properties of conventional semiconductors. However, how isotopic mass affects the optoelectronic properties in 2D semiconductors remains unclear because of measurement uncertainties resulting from sample heterogeneities. Here, we report an anomalous optical bandgap energy red shift of 13 (±7) milli–electron volts as mass of Mo isotopes is increased in laterally structured 100 MoS 2 - 92 MoS 2 monolayers grown by a two-step chemical vapor deposition that mitigates the effects of heterogeneities. This trend, which is opposite to that observed in conventional semiconductors, is explained by many-body perturbation and time-dependent density functional theories that reveal unusually large exciton binding energy renormalizations exceeding the ground-state renormalization energy due to strong coupling between confined excitons and phonons. The isotope effect on the optical bandgap reported here provides perspective on the important role of exciton-phonon coupling in the physical properties of two-dimensional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Directly visualizing the momentum-forbidden dark excitons and their dynamics in atomically thin semiconductors

Resolving momentum degrees of freedom of excitons, which are electron-hole pairs bound by the Coulomb attraction in a photoexcited semiconductor, has remained an elusive goal for decades. In atomically thin semiconductors, such a capability could probe the momentum-forbidden dark excitons, which critically affect proposed opto-electronic technologies but are not directly accessible using optical techniques. In this work, we probed the momentum state of excitons in a tungsten diselenide monolayer by photoemitting their constituent electrons and resolving them in time, momentum, and energy. We obtained a direct visual of the momentum-forbidden dark excitons and studied their properties, including their near degeneracy with bright excitons and their formation pathways in the energy-momentum landscape. These dark excitons dominated the excited-state distribution, a surprising finding that highlights their importance in atomically thin semiconductors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Photoluminescence and Raman spectroscopy of wide bandgap semiconductors damaged by deep-UV laser irradiation

The effects of a pulsed, focused, deep-UV (4.66 eV) laser on wide and ultra-wide bandgap semiconductors were investigated with photoluminescence (PL) and Raman spectroscopy. Three semiconductor single crystals were studied: silicon carbide (6H-SiC), gallium nitride (GaN), and gallium oxide (β-Ga 2 O 3 ). Atomic emission lines from neutral Ga or Si were observed during the laser-damage process. For all three semiconductors, PL mapping (3.49 eV laser excitation) of the damaged material revealed visible emission bands in the 2.6–2.8 eV range, attributed to point defects. Raman spectra (2.33 eV excitation) showed a reduction in the Raman peak intensities in the damaged region, along with weak PL bands around 1.9–2.1 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding Novel Lewis Acid Doping Mechanisms in Organic Semiconductors

Recent studies supported by this DOE grant have provided a more detailed understanding of the doping mechanism of organic semiconductors by the Lewis acid, tris(pentafluorophenyl)borane (BCF). Our studies have examined the intermolecular semiconductor-dopant interactions as well as the thermodynamic feasibility of different doping mechanisms. Most notably, we found a different proposed doping scheme is much more thermodynamically favoured (exergonic) than our proposed two-step BCF doping mechanism. The state-of-the-art experimental and theoretical techniques of High-Field Multi-Dimensional Solid State NMR spectroscopy and Time-Dependent Density Functional theory (TD-DFT) and DFT were employed in this work. The data obtained helped identify the structural details and intermolecular interactions which impact the organic semiconductor doping efficiency for BCF and how these compare to the case of doping by the standard integer charge transfer dopant molecule F 4 TCNQ. We have, for the first time, assigned specific chemical shift values for the F 4 TCNQ molecules clustered outside of polymer chains as well as those intercalated between the polymer backbones. Further, we provide theoretical support for a novel doping mechanism which combines those proposed in previous literature involving the evolution of hydrogen gas along with a doping species more complex than the simple BCF·H 2 O. While our previously proposed doping mechanism was found to be highly thermodynamically unfavorable, the formation of large anion [BCF(OH)(OH 2 )BCF]- is the key change making the proposed mechanism exergonic while the elimination of gaseous H 2 helps drive the doping reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Multiplication of Freestanding Compound Semiconductor Membranes from a Single Wafer by Alternating Growth with 2D Materials

Single-crystal compound semiconductors, such as III-N and III-V, are important building blocks for functional devices due to their high electron mobilities, wide range of bandgaps, and excellent optoelectronic properties. However, current methods to produce their freestanding membranes for heterointegration suffer from slow processes or poor material quality. Here, we demonstrate an approach to grow and harvest multiple wafer-scale single-crystal membranes with high throughput by introducing weak van der Waals interfaces between epitaxial layers. This is achieved by directly growing two-dimensional (2D) materials on compound semiconductors in their native deposition systems, which enables alternating growth of 2D material and compound semiconductor epitaxial layers in a single run. Each epilayer in the multi-stack structure is then sequentially harvested by mechanical exfoliation, producing multiple freestanding single-crystal membranes with extremely high throughput from a single wafer, primed for integration in mixed-dimensional heterostructures.

Han, Ne Myo↗
DOE OSTI2022

Multiplication of Freestanding Compound Semiconductor Membranes from a Single Wafer by Alternating Growth with 2D Materials

Single-crystal compound semiconductors, such as III-N and III-V, are important building blocks for functional devices due to their high electron mobilities, wide range of bandgaps, and excellent optoelectronic properties. However, current methods to produce their freestanding membranes for heterointegration suffer from slow processes or poor material quality. Here, we demonstrate an approach to grow and harvest multiple wafer-scale single-crystal membranes with high throughput by introducing weak van der Waals interfaces between epitaxial layers. This is achieved by directly growing two-dimensional (2D) materials on compound semiconductors in their native deposition systems, which enables alternating growth of 2D material and compound semiconductor epitaxial layers in a single run. Each epilayer in the multi-stack structure is then sequentially harvested by mechanical exfoliation, producing multiple freestanding single-crystal membranes with extremely high throughput from a single wafer, primed for integration in mixed-dimensional heterostructures.

Han, Ne Myo↗
DOE OSTI2026

Intermediate Bandgap (IB) Cu 3 VS x Se 4−x Nanocrystals as a New Class of Light Absorbing Semiconductors

A new family of highly uniform, cubic-shaped Cu 3 VS x Se 4−x (CVSSe; 0 ≤ x ≤ 4) nanocrystals based on earth-abundant materials with intermediate bandgaps (IB) in the visible range is reported, synthesized via a hot-injection method. The IB transitions and optical band gap of the novel CVSSe nanocrystals are investigated using ultraviolet-visible spectroscopy, revealing tunable band gaps that span the visible and near-infrared regimes. The composition-dependent relationships among the crystal phase, optical band gap, and photoluminescence properties of the novel IB semiconductors with progressive substitution of Se by S are examined in detail. High-resolution transmission electron microscopy and scanning electron microscopy characterization confirm the high crystallinity and uniform size (~19.7 nm × 17.2 nm for Cu 3 VS 4 ) of the cubic-shaped nanocrystals. Density functional theory (DFT) calculations based on virtual crystal approximation support the experimental findings, showing good agreement in lattice parameters and band gaps across the CVSSe series and lending confidence that the targeted phases and compositions have been successfully realized. A current conversion efficiency, i.e., incident photon-to-current efficiency, of 14.7% was achieved with the p-type IB semiconductor Cu 3 VS 4 . These novel p-type IB semiconductor nanocrystals hold promise for enabling thin film solar cells with efficiencies beyond the Shockley–Queisser limit by allowing sub-band-gap photon absorption through intermediate-band transitions, in addition to the conventional direct-band-gap transition.

Cu3VSxSe4−x↗
DOE OSTI2020

Using a carbon vacancy reduction material to increase average carrier lifetime in a silicon carbide semiconductor device

A semiconductor die and a process for fabricating the semiconductor die are disclosed. The semiconductor die has a substrate and a silicon carbide (SiC) epitaxial structure on the substrate. The SiC epitaxial structure includes at least a first N-type SiC layer, at least a first P-type SiC layer, and carbon vacancy reduction material, which has been implanted into a surface of the SiC epitaxial structure. Further, the SiC epitaxial structure has been annealed to mobilize the carbon vacancy reduction material to diffuse carbon atoms substantially throughout the SiC epitaxial structure, thereby increasing an average carrier lifetime in the SiC epitaxial structure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Systems and methods for organic semiconductor devices with sputtered contact layers

Systems and methods for organic semiconductor devices with sputtered contact layers are provided. In one embodiment, an organic semiconductor device comprises: a first contact layer (140) comprising a first sputter-deposited transparent conducting oxide; an electron transport layer (130) interfacing with the first contact layer; a second contact layer (110) comprising a second sputter-deposited transparent conducting oxide; a hole transport layer interfacing with the second contact layer; and an organic semiconductor active layer (120) having a first side facing the electron transport layer and an opposing second side facing the hole transport layer; wherein either the electron transport layer or the hole transport layer comprises a buffering transport layer.

Hammond, Scott R.↗
DOE OSTI2020

Evaluation of radiation hardness of semiconductor materials against alpha particles for an API detector

An Associated Particle Imaging (API) system consists of a high vacuum chamber where deuterium ions are accelerated on a tritium-loaded target, resulting in alpha particles and neutrons emitted back-to-back, the latter escaping the chamber and used, for example, for tomography of a high-Z sample. An accurate determination of the alpha position is crucial to determine the trajectory of the neutron. Existing API systems have several limitations which a semiconductor-based API detector placed inside the vacuum chamber should not present. The semiconductor material can be either silicon or diamond. In particular, large and fast signals are generated by the alpha interactions in these materials. A pixelated API detector will measure the time and hit position of the alphas produced in the reaction. However, during the lifetime of the generator, the semiconductor detector will be exposed to an intense flux of alpha particles that will degrade its performance over time. To assess the radiation hardness of silicon and diamond against the alpha particles, we exposed single diodes made of either of the two materials to a 5 MeV alpha flux generated by an 241Am radioactive source. During irradiation, the diodes were biased and mounted on current-sensitive preamplifier boards. We have therefore been able to measure insitu the evolution of the waveforms as the damage was accumulating in their substrates.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Methods and devices for fabricating and assembling printable semiconductor elements

The invention provides methods and devices for fabricating printable semiconductor elements and assembling printable semiconductor elements onto substrate surfaces. Methods, devices and device components of the present invention are capable of generating a wide range of flexible electronic and optoelectronic devices and arrays of devices on substrates comprising polymeric materials. The present invention also provides stretchable semiconductor structures and stretchable electronic devices capable of good performance in stretched configurations.

Nuzzo, Ralph G.↗
DOE OSTI2021

Generation and enhancement of surface acoustic waves on a highly doped p-type III-V semiconductor substrate

A device employing the generation and enhancement of surface acoustic waves on a highly doped p-type III-V semiconductor substrate (e.g., GaAs, GaSb, InAs, or InGaAs). The device includes two SiO 2 /ZnO islands, each including a SiO 2 buffer layer deposited on the doped p-type III-V semiconductor substrate and a ZnO layer deposited on the SiO 2 buffer layer. An input interdigital transducers (IDT) and an output IDT are each patterned on one of the SiO 2 /ZnO islands. The IDTs generates surface acoustic waves along an exposed surface of the highly doped p-type III-V semiconductor substrate. The surface acoustic waves improve the photoelectric and photovoltaic properties of the device. The device is manufactured using a disclosed technique for propagating strong surface acoustic waves on weak piezoelectric materials. Also disclosed is a photodetector developed using that technique.

Dong, Boqun↗
DOE OSTI2022

Predicting failure parameters of semiconductor devices subjected to stress conditions

A method for predicting failure parameters of semiconductor devices can include receiving a set of data that includes (i) characteristics of a sample semiconductor device, and (ii) parameters characterizing a stress condition. The method further includes extracting a plurality of feature values from the set of data and inputting the plurality of feature values into a trained model executing on the one or more processors, wherein the trained model is configured according to an artificial intelligence (AI) algorithm based on a previous plurality of feature values, and wherein the trained model is operable to output a failure prediction based on the plurality of feature values. Further, the method includes generating, via the trained model, a predicted failure parameter of the sample semiconductor device due to the stress condition.

Ahmed, Moinuddin↗
DOE OSTI2023

Systems and methods for organic semiconductor devices with sputtered contact layers

Systems and methods for organic semiconductor devices with sputtered contact layers are provided. In one embodiment, an organic semiconductor device comprises: a first contact layer comprising a first sputter-deposited transparent conducting oxide; an electron transport layer interfacing with the first contact layer; a second contact layer comprising a second sputter-deposited transparent conducting oxide; a hole transport layer interfacing with the second contact layer; and an organic semiconductor active layer having a first side facing the electron transport layer and an opposing second side facing the hole transport layer; wherein either the electron transport layer or the hole transport layer comprises a buffering transport layer.

Hammond, Scott R.↗
DOE OSTI2024

Systems and methods for organic semiconductor devices with sputtered contact layers

Systems and methods for organic semiconductor devices with sputtered contact layers are provided. In one embodiment, an organic semiconductor device comprises: a first contact layer comprising a first sputter-deposited transparent conducting oxide; an electron transport layer interfacing with the first contact layer; a second contact layer comprising a second sputter-deposited transparent conducting oxide; a hole transport layer interfacing with the second contact layer; and an organic semiconductor active layer having a first side facing the electron transport layer and an opposing second side facing the hole transport layer; wherein either the electron transport layer or the hole transport layer comprises a buffering transport layer.

Hammond, Scott R.↗
DOE OSTI2023

Solution-Phase Synthesis and Photoluminescence of Quaternary Chalcohalide Semiconductors

Mixed-metal chalcohalide semiconductors have emerged as promising candidates for photovoltaic applications. However, preparation of these multinary compounds using solution-phase techniques remains particularly challenging compared to traditional solid-state methods. To fully harness their potential, it is desirable to develop synthetic methods that enable control over both the phase purity and dimensionality of chalcohalides. In this work, we report the solution-phase synthesis of Pb 2 SbS 2 I 3 and Pb 2 BiS 2 I 3 quaternary chalcohalides using readily available precursors. Fine tuning of reaction parameters allows for the isolation of rod-like morphologies with tunable diameters and aspect ratios. The quaternary chalcohalides display photoluminescence as an ensemble as well as at the single particle level, as demonstrated using fluorescence microscopy. We further evaluate the relative stability and band gap of Pb 2 SbS 2 I 3 polymorphs and their coloring patterns using electronic structure calculations. The synthetic methods developed here will motivate the study of ever more complex chalcohalides and other multinary semiconductors for new technological applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗