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At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

DOE OSTI2021

On the Equilibrium Electrostatic Potential and Light-Induced Charge Redistribution in Halide Perovskite Structures

Lead halide perovskites are semiconductor materials which are employed as nonintentionally doped absorbers inserted between two selective carrier transport layers (SCTL), realizing a p-i-n or n-i-p heterojunction. In our study, we have developed and investigated a lateral device, based on methylammonium lead iodide (MAPbI3) in which the p-i-n heterojunction develops in the horizontal direction. Our research suggests that the effective doping level in the MAPbI3 film should be very low, below 1012 cm-3. Along the vertical direction, this doping level is not enough to screen the electric field of the buried heterojunction with the SCTL. The perovskite work function is therefore affected by the work function of the SCTL underneath. From drift-diffusion simulations, we show that intrinsic perovskite-SCTL structures develop mV range surface photovoltages (SPVs) under continuous illumination. However, perovskite-SCTL structures can develop SPVs of hundreds of mV, as confirmed by our measurements. We therefore analyzed the compatibility between low doping and low defect densities in the perovskite layer and such high SPV values using numerical modeling. It is shown that these high SPV values could originate from electronic processes due to large band offsets in the buried perovskite-SCTL heterojunctions, or at the SCTL-transparent conductive oxide (TCO) buried heterojunction. However, such electronic processes can hardly explain the long SPV persistence after switching off the illumination.

defects↗

DOE OSTI2023

Switch leakage mitigation through differential cancellation

High speed analog-to-digital converters (ADC), switched-capacitor delay elements, and pulsed radio frequency (RF) systems all require switches in the signal path operating at high switching speeds, providing low resistance when enabled, and providing high signal isolation when disabled. In semiconductor technologies such as CMOS, the enabled state resistance directly scales with the sizing of the switch device, where a larger width switch provides a lower enabled state resistance. As the device width is increased, so is the capacitance formed between the gate, drain, and source of the device.

42 ENGINEERING↗

DOE OSTI2022

Thermal Optimization of a Silicon Carbide, Half-Bridge Power Module

This project describes the modeling process to design the packaging and heat exchanger for a half-bridge wide-bandgap (WBG) power semiconductor module. The module uses two silicon carbide, metal-oxide-semiconductor field-effect transistor (MOSFET) devices per switch position that are soldered to an aluminum nitride, direct-bond copper (DBC) substrate. A baseplate cooling configuration (e.g., no thermal grease) is used along with a water-ethylene glycol, jet-impingement-style heat exchanger. The heat exchanger was designed to be fabricated using prototyping equipment from the National Renewable Energy Laboratory, complies with automotive standards (for minimal channel sizes, flow rates, and coolant), and considers reliability aspects (i.e., erosion/corrosion). Device-scale computational fluid dynamics (CFD) is used first to design the slot jet impingement cooling configuration and compute the effective heat transfer coefficient (HTC) of the concept. The computed HTCs are then used as boundary conditions for a finite element study to optimize the package geometry (e.g., device layout and baseplate thickness) to minimize thermal resistance and minimize temperature variation between the module's four devices. Finally, a fluid manifold is designed to generate the slot jets and cool the devices. Module-scale CFD predicts a relatively low junction-to-fluid thermal resistance of 16.7 mm2 K/W, a 1.4 degrees C temperature variation between devices, and a total pressure drop of 5,860 Pa (0.85 psi) for the design. The thermal resistance of the module design is about 67% lower than the 2015 BMW i3 power electronics/modules thermal resistance.

DIRECT ENERGY CONVERSION↗

NASA NTRS1979

Diode step stress testing program for JANTX1N5550

The effect was studied of power/temperature step stress when applied to the switching diode JANTX1N5550 manufactured by Semtech and Micro Semiconductor. The power/temperature stress tests are presented, and failure analyses are included.

Source record↗

NASA NTRS1979

Diode step stress program for JANTX1N5552

The effect of power/temperature step stress when applied to the switching diode JANTX1N5554 manufactured by Semtech and Micro Semiconductor was evaluated. A total of 48 samples from each manufacturer were submitted to the process outlined. In addition, two control sample units were maintained for verification of the electrical parametric testing.

Source record↗

NASA NTRS1979

Diode step stress program for JANTX1N5615

The effect of power/temperature step stress when applied to the switching diode JANTX1N5615 manufactured by Semtech and Micro semiconductor was examined. A total of 48 samples from each manufacturer were submitted to the process. In addition, two control sample units were maintained for verification of the electrical parametric testing. All test samples were subjected to the electrical tests after completing the prior power/temperature step stress point. Results are presented.

Source record↗

NASA NTRS1979

Diode step stress program for JANTX1N5623

The effect of power/temperature step stress was studied when applied to the switching diode JANTX1N5623 manufactured by Semtech and Micro Semiconductor. Test results and failure analyses are included.

Source record↗

NASA NTRS1979

Diode step stress testing program for JANTX1N5618

The effect of power/temperature step stress when applied to the switching diode JANTX1N5618 manufactured by Semtech and Micro Semiconductor is reported. A total of 48 samples from each manufacturer was submitted to the process. In addition, two control sample units were maintained for verification of the electrical parametric testing.

Source record↗

DOE OSTI2022

Slow light in a 2D semiconductor plasmonic structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons interacting with excitons in a semiconductor monolayer. Here, we use coupled exciton-surface plasmon polaritons (E-SPPs) in monolayer WSe 2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear E-SPP response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 105 m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.

42 ENGINEERING↗

DOE OSTI2025

Aluminum Boron Nitride Ferroelectric Field-Effect Transistors With ZnO Semiconductor Channel

The discovery of ferroelectricity in hafnium zirconium oxide (HfxZr 1−x O2) and related fluorite materials has spurred interest in ferroelectric devices suitable for integration with silicon integrated circuits (ICs), especially those that can be embedded in the back-end-of-line (BEOL) process. More recently, ferroelectricity has been found in wurtzite aluminum nitride-based materials, such as scandium and boron-doped aluminum nitride (Al 1−x ScxN and Al 1−x BxN). Although these materials currently have undesirably large coercive electric fields, and small breakdown electric field-to-coercive electric field ratio, their low processing temperatures and large remanent polarization offer intriguing possibilities for device applications. Furthermore, we report ferroelectric field-effect transistors (FeFETs) with a 15 nm thick Al0.88B0.12N layer and an 11 nm ZnO semiconductor channel, achieving a memory window >1 V and switching voltages ( V switch ) <±10 V.

42 ENGINEERING↗

DOE OSTI2023

Enhanced Switching Reliability of Hf 0.5 Zr 0.5 O 2 Ferroelectric Films Induced by Interface Engineering

Ferroelectric materials have been widely researched for applications in memory and energy storage. Among these materials and benefiting from their excellent chemical compatibility with complementary metal–oxide–semiconductor (CMOS) devices, hafnia-based ferroelectric thin films hold great promise for highly scaled semiconductor memories, including nonvolatile ferroelectric capacitors and transistors. However, variation in the switched polarization of this material during field cycling and a limited understanding of the responsible mechanisms have impeded their implementation in technology. Here, we show that ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) capacitors that are nearly free of polarization “wake-up”─a gradual increase in switched polarization as a function of the number of switching cycles─can be achieved by introducing ultrathin HfO 2 buffer layers at the HZO/electrodes interface. High-resolution transmission electron microscopy (HRTEM) reveals crystallite sizes substantially greater than the film thickness for the buffer layer capacitors, indicating that the presence of the buffer layers influences the crystallization of the film (e.g., a lower ratio of nucleation rate to growth rate) during postdeposition annealing. This evidently promotes the formation of a polar orthorhombic (O) phase in the as-fabricated buffer layer samples. Synchrotron X-ray diffraction (XRD) reveals the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase during electric field cycling in the control (no buffer) devices, consistent with the polarization wake-up observed for these capacitors. The extent of T–O transformation in the nonbuffer samples is directly dependent on the duration over which the field is applied. Here these results provide insight into the role of the HZO/electrodes interface in the performance of hafnia-based ferroelectrics and the mechanisms driving the polarization wake-up effect.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Defect Chemistry and Doping of Ultrawide Band Gap (III)BO 3 Compounds

New wide band gap semiconductors are needed to increase the power, voltage, and switching frequency limits of power electronic devices. A recent computational search identified a family of ultrawide band gap (4.8-7.8 eV) group-III orthoborates as promising materials for power electronics, assuming n-type doping could be attained. In this report we test this assumption by investigating the defect chemistry and dopability of rhombohedral calcite-structured AlBO 3 , GaBO 3 , and InBO 3 using first-principles calculations. Of the three, we find InBO 3 to have the most potential for n-type doping without significant compensation by native acceptor defects. Furthermore, Zr is predicted to readily substitute for In and behave as a shallow donor with maximal net donor concentrations exceeding 1 x 10 18 cm -3 under growth conditions typical for this class of materials. We also demonstrate thin film growth of InBO3 and measure its absorption onset, which we find to be consistent with theory. Ultimately, our results confirm the promise of InBO 3 as an n-type ultrawide band gap semiconductor and point to alloying with GaBO 3 and AlBO 3 for further optimization of band gap and electron concentration for high-power applications.

36 MATERIALS SCIENCE↗

NASA NTRS2016

Silicon-Carbide Power MOSFET Performance in High Efficiency Boost Power Processing Unit for Extreme Environments

Silicon-Carbide device technology has generated much interest in recent years. With superior thermal performance, power ratings and potential switching frequencies over its Silicon counterpart, Silicon-Carbide offers a greater possibility for high powered switching applications in extreme environment. In particular, Silicon-Carbide Metal-Oxide- Semiconductor Field-Effect Transistors' (MOSFETs) maturing process technology has produced a plethora of commercially available power dense, low on-state resistance devices capable of switching at high frequencies. A novel hard-switched power processing unit (PPU) is implemented utilizing Silicon-Carbide power devices. Accelerated life data is captured and assessed in conjunction with a damage accumulation model of gate oxide and drain-source junction lifetime to evaluate potential system performance at high temperature environments.

Ikpe, Stanley A.↗

NASA NTRS2006

Submicrosecond Power-Switching Test Circuit

A circuit that changes an electrical load in a switching time shorter than 0.3 microsecond has been devised. This circuit can be used in testing the regulation characteristics of power-supply circuits . especially switching power-converter circuits that are supposed to be able to provide acceptably high degrees of regulation in response to rapid load transients. The combination of this power-switching circuit and a known passive constant load could be an attractive alternative to a typical commercially available load-bank circuit that can be made to operate in nominal constant-voltage, constant-current, and constant-resistance modes. The switching provided by a typical commercial load-bank circuit in the constant-resistance mode is not fast enough for testing of regulation in response to load transients. Moreover, some test engineers do not trust the test results obtained when using commercial load-bank circuits because the dynamic responses of those circuits are, variously, partly unknown and/or excessively complex. In contrast, the combination of this circuit and a passive constant load offers both rapid switching and known (or at least better known) load dynamics. The power-switching circuit (see figure) includes a signal-input section, a wide-hysteresis Schmitt trigger that prevents false triggering in the event of switch-contact bounce, a dual-bipolar-transistor power stage that drives the gate of a metal oxide semiconductor field-effect transistor (MOSFET), and the MOSFET, which is the output device that performs the switching of the load. The MOSFET in the specific version of the circuit shown in the figure is rated to stand off a potential of 100 V in the "off" state and to pass a current of 20 A in the "on" state. The switching time of this circuit (the characteristic time of rise or fall of the potential at the drain of the MOSFET) is .300 ns. The circuit can accept any of three control inputs . which one depending on the test that one seeks to perform: a repetitive waveform from a signal generator, momentary closure of a push-button switch, or closure or opening of a manually operated on/off switch. In the case of a signal generator, one can adjust the frequency and duty cycle as needed to obtain the desired AC power-supply response, which one could display on an oscilloscope. Momentary switch closure could be useful for obtaining (and, if desired, displaying on an oscilloscope set to trigger on an event) the response of a power supply to a single load transient. The on/off switch can be used to switch between load states in which static-load regulation measurements are performed.

Folk, Eric N.↗

DOE OSTI2025

Theoretical perspective on phase stability and polarization switching in ferroelectric hafnia

Fluorite-based ferroelectric materials are revolutionizing the application space of polar semiconductors. These materials leverage robust polarization of extremely thin films, compatibility with the silicon chip processing, and decades of manufacturing experience to enable a new generation of ferroelectric memory devices. As a new paradigm for ferroelectrics, understanding of phase transitions and the switching mechanism in fluorites is essential both for advancing applications and for fundamental science. In this article, we outline the recent progress that has been made to understand the relative phase stability, phase transition and order parameter coupling, ferroelectric switching through unique nucleation and growth processes, and how defects affect these phases and processes. The main challenges, opportunities, and next steps for leveraging these materials for next-generation devices are reviewed.

Condensed Matter Physics↗

DOE OSTI2022

How arsenic makes amorphous GeSe a robust chalcogenide glass for advanced memory integration

The 3D integration technology in semiconductor fabrication requires a key component, the ovonic threshold switching (OTS) selector, to suppress the current leakage. The As doped amorphous (a-) GeSe glass is a commercialized OTS material in 3D phase-change memory, but the understanding of such a doping mechanism is still inadequate. Here we systematically explore the effect of As doping on the structural, bonding, and dynamics properties of a-GeAsSe using ab initio molecular dynamics simulations. The results reveal that As atoms form strong bonds with both Ge and Se atoms. The distorted octahedral structures and the 5-fold rings linked by atoms are increased. All of these structural features lead to a more disordered configuration. Moreover, as atoms have notably slowed down the atomic mobility, rendering a-GeAsSe a high stability. Overall, our studies offer insightful understanding of As-doping in OTS materials, paving the way for the design and application of advanced selector devices.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Controlling the helicity of light by electrical magnetization switching

Controlling the intensity of emitted light and charge current is the basis of transferring and processing information. By contrast, robust information storage and magnetic random-access memories are implemented using the spin of the carrier and the associated magnetization in ferromagnets. In this study, the missing link between the respective disciplines of photonics, electronics and spintronics is to modulate the circular polarization of the emitted light, rather than its intensity, by electrically controlled magnetization. Here we demonstrate that this missing link is established at room temperature and zero applied magnetic field in light-emitting diodes through the transfer of angular momentum between photons, electrons and ferromagnets. With spin-orbit torque a charge current generates also a spin current to electrically switch the magnetization. This switching determines the spin orientation of injected carriers into semiconductors, in which the transfer of angular momentum from the electron spin to photon controls the circular polarization of the emitted light. The spin-photon conversion with the nonvolatile control of magnetization opens paths to seamlessly integrate information transfer, processing and storage. Our results provide substantial advances towards electrically controlled ultrafast modulation of circular polarization and spin injection with magnetization dynamics for the next-generation information and communication technology, including space-light data transfer. The same operating principle in scaled-down structures or using two-dimensional materials will enable transformative opportunities for quantum information processing with spin-controlled single-photon sources, as well as for implementing spin-dependent time-resolved spectroscopies.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1966

MOSFET analog memory circuit achieves long duration signal storage

Memory circuit maintains the signal voltage at the output of an analog signal amplifier when the input signal is interrupted or removed. The circuit uses MOSFET /Metal Oxide Semiconductor Field Effect Transistor/ devices as voltage-controlled switches, triggered by an external voltage-sensing device.

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