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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

High efficiency single Ag nanowire/p-GaN substrate Schottky junction-based ultraviolet light emitting diodes

We report a high efficiency single Ag nanowire (NW)/p-GaN substrate Schottky junction-based ultraviolet light emitting diode (UV-LED). The device demonstrates deep UV free exciton electroluminescence at 362.5 nm. The dominant emission, detectable at ultralow (<1 μA) forward current, does not exhibit any shifts when the forward current is increased. External quantum efficiency (EQE) as high as 0.9% is achieved at 25 μA current at room temperature. Experiments and simulation analysis show that devices fabricated with thinner Ag NWs have higher EQE. However, for very thin Ag NWs (diameter < 250 nm), this trend breaks down due to heat accumulation in the NWs. Our simple device architecture offers a potentially cost-effective scheme to fabricate high efficiency Schottky junction-based UV-LEDs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Carrier capture and emission by substitutional carbon impurities in GaN vertical diodes

A model was developed for the operation of a GaN pn junction vertical diode which includes rate equations for carrier capture and thermally activated emission by substitutional carbon impurities and carrier generation by ionizing radiation. The model was used to simulate the effect of ionizing radiation on the charge state of carbon. These simulations predict that with no applied bias, carbon is negatively charged in the n-doped layer, thereby compensating n-doping as experimentally observed in diodes grown by metal-organic chemical vapor deposition. With reverse bias, carbon remains negative in the depletion region, i.e., compensation persists in the absence of ionization but is neutralized by exposure to ionizing radiation. This increases charge density in the depletion region, decreases the depletion width, and increases the capacitance. The predicted increase in capacitance was experimentally observed using a pulsed 70 keV electron beam as the source of ionization. In additional confirming experiments, the carbon charge-state conversion was accomplished by photoionization using sub-bandgap light or by the capture of holes under forward bias.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Impulse Response Functions for Characterizing Pulse-to-Pulse Junction Temperature Behavior in Laser Diode Pulse Trains

A method is proposed for determination of the pulse-to-pulse variation in junction temperature and emission wavelength of a semiconductor laser diode during a train of pulses. Here, this approach, based on impulse response functions, enables predictions for pulse trains with arbitrary pulse-to-pulse variations in output power, pulse width, and pulse delay using a limited set of experimental characterization data. The use of this approach is illustrated by application to a particular device structure.

Deri, Robert J. [Lawrence Livermore National Labor↗
DOE OSTI2012

Anisotropic transport properties of zinc-blend ZnTe/CrTe heterogeneous junction nanodevices

Motivated by the molecular-beam epitaxial growth of zinc-blend-type CrTe thin films on ZnTe, we present a theoretical study on the spin-polarized transport properties of ZnTe/CrTe p-n junction as spin diode and CrTe/ZnTe/CrTe magnetic tunnel junction for (001) and (011) surfaces. Both ZnTe(001)/CrTe(001) and ZnTe(011)/CrTe(011) p-n junctions show excellent spin diode effect, the majority spin current of positive voltage is much larger than that of negative voltage and the minority spin current is absolutely inhibited. The ZnTe(001)/CrTe(001) p-n junction has lower 'turn off' current and higher rectification ratio (about 10{sup 5}) than the ZnTe(011)/CrTe(011) which shows obvious anisotropy. We also find that the tunneling magneto resistance ratio of the CrTe/ZnTe/CrTe magnetic tunnel junction is up to about 4 Multiplication-Sign 10{sup 9}%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Characterization of a n+3C/n−4H SiC heterojunction diode

We report on the fabrication of n + 3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to ∼7 × 10{sup 17 }cm{sup −3} dopant impurity concentration. The conduction band off-set is about 1 V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n + 3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2011

Extension of the ADC Charge-Collection Model to Include Multiple Junctions

The ADC model is a charge-collection model derived for simple p-n junction silicon diodes having a single reverse-biased p-n junction at one end and an ideal substrate contact at the other end. The present paper extends the model to include multiple junctions, and the goal is to estimate how collected charge is shared by the different junctions.

drift-diffusion↗
DOE OSTI2014

Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junctions

The development of light-emitting diodes with improved efficiency, spectral properties, compactness and integrability is important for lighting, display, optical interconnect, logic and sensor applications1, 2, 3, 4, 5, 6, 7, 8. Monolayer transition-metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties9, 10, 11, 12, 13, 14, 15, 16. Electroluminescence has already been observed from monolayer MoS2 devices17, 18. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of the MoS2 and to ineffective contacts. Here, we report electroluminescence from lateral p–n junctions in monolayer WSe2 induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe2, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than in MoS2 (refs 17,18). Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. This system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Gallium phosphide high temperature diodes

High temperature (300 C) diodes for geothermal and other energy applications were developed. A comparison of reverse leakage currents of Si, GaAs, and GaP was made. Diodes made from GaP should be usable to 500 C. A Liquid Phase Epitaxy (LPE) process for producing high quality, grown junction GaP diodes is described. This process uses low vapor pressure Mg as a dopant which allows multiple boat growth in the same LPE run. These LPE wafers were cut into die and metallized to make the diodes. These diodes produce leakage currents below ten to the -9th power A/sq cm at 400 C while exhibiting good high temperature rectification characteristics. High temperature life test data is presented which shows exceptional stability of the V-I characteristics.

Chaffin, R. J.↗
DOE OSTI2020

Aging Effect Analysis of PV Inverter Semiconductors for Ancillary Services Support

PV inverters can provide reactive power while generating active power. An ongoing microgrid implementation at Duke Energy actively engages non-utility PVs to generate/absorb reactive power in support of ancillary services to increase microgrid resiliency during extreme events. PV systems are requested to provide reactive power support: 1) in response to grid voltage variation to better regulate the local voltage; or 2) in response to utility incentives, such as following Transactive Energy System (TES) incentives. However, providing ancillary services might shorten the lifetime expectation of PV inverter semiconductors. This paper summarizes the potential impacts on a PV inverter semiconductor's lifetime when providing ancillary services. The analysis presented in this research work shows that providing reactive power support will increase the mean junction temperature and the junction temperature variation of the inverter diodes. This increased junction temperature will eventually lead to shorter diode lifetime. The lifetime estimation of semiconductors is briefly reviewed. The power losses of PV inverter semiconductors are derived as a support analysis to the junction temperature calculation. In addition, the impact of the filtering inductor on the semiconductor current distribution is discussed. The theoretical analysis presented in this research work is supported by simulation results.

14 SOLAR ENERGY↗
DOE OSTI2021

All-MOCVD-grown gallium nitride diodes with ultra-low resistance tunnel junctions

In this work, we carefully investigate three important effects including postgrowth activation annealing, delta (δ) dose and magnesium (Mg) buildup delay as well as experimentally demonstrate their influence on the electrical properties of GaN homojunction p–n diodes with a tunnel junction (TJ). The diodes were monolithically grown by metalorganic chemical vapor deposition (MOCVD) in a single growth step. By optimizing the annealing parameters for Mg activation, δ-dose for both donors and acceptors at TJ interfaces, and p + -GaN layer thickness, a significant improvement in tunneling properties is achieved. For the TJs embedded within the continuously-grown, all-MOCVD GaN diode structures, ultra-low voltage penalties of 158 mV and 490 mV are obtained at current densities of 20 A cm –2 and 100 A cm –2 , respectively. The diodes with the engineered TJs show a record-low differential resistivity of 1.6 × 10 –4 Ω cm 2 at 5 kA cm –2 .

42 ENGINEERING↗
NASA NTRS1965

Solid-state detector

Solid state detector - N type silicon surface barrier diode as microparticle detector

SOLID STATE DEVICE↗
DOE OSTI2021

Dual Phase Change Thermal Diodes with High Rectification for Thermal Management near Room Temperature

Thermal diodes are passive systems that modulate their thermal resistance depending on the direction of temperature gradient, thereby allowing preferential directional heat flow. A dual phase thermal diode consists of a junction between two phase change materials that have opposing temperature-dependent thermal conductivity trends, and whose performance (i.e., rectification ratio) is related to the ratio of the thermal conductivities of the different phases. In this work, a dual phase change diode with a rectification ratio of ~3.5 for an applied temperature bias of ~40 K is presented, which is among the highest-performing junction diodes based on phase change materials at the macroscale for near room temperature applications. The diode is composed of an aqueous solution of poly(N-isopropylacrylamide), a thermo-responsive polymer, and calcium chloride hexahydrate -- a solid-liquid phase change material. Experimental insights are provided into the contributions of different heat transfer mechanisms, conduction, and convection, and the effect of concentration of the thermo-responsive polymer.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Extension of the Mott–Gurney Law for a Bilayer Gap

Steady drift states of an electron flow in a planar gap filled with a bilayer dielectric have been considered. Exact mathematical formulas have been derived that describe the distributions of the electrostatic potential and space charge limited electron flow current (extended Mott–Gurney law for a bilayer diode).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1996

InP tunnel junctions for InP/InGaAs tandem solar cells

We report, for the first time, an epitaxially grown InP p(+)/n(++) tunnel junction. A diode with peak current densities up to 1600 A/cm and maximum specific resistivities (Vp/Ip - peak voltage to peak current ratio) in the range of 10(exp -4)Omega cm(exp 2) is obtained. This peak current density is comparable to the highest results previously reported for lattice matched In(0.53)Ga(0.47)As tunnel junctions. Both results were obtained using chemical beam epitaxy (CBE). In this paper we discuss the electrical characteristics of these tunnel diodes and how the growth conditions influence them.

Vilela, Mauro F.↗
NASA NTRS1995

InP Tunnel Junctions for InP/InGaAs Tandem Solar Cells

We report, for the first time, an epitaxially grown InP p(+)/n(++) tunnel junction. A diode with peak current densities up to 1600 Al/sq cm and maximum specific resistivities (Vp/lp - peak voltage to peak current ratio) in the range of 10(exp -4)Om sq cm is obtained. This peak current density is comparable to the highest results previously reported for lattice matched In(0.53)Ga(0.47)As tunnel junctions. Both results were obtained using chemical beam epitaxy (CBE). In this paper we discuss the electrical characteristics of these tunnel diodes and how the growth conditions influence them.

Vilela, M. F.↗