Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

  • About the Lab
  • People
  • Research
  • Publications
  • Outreach
  • Facilities
  • News

Sieun presents at APS March Meeting!

March 23, 2021 By Matt Webb

Sieun gave a virtual talk at the American Physical Society (APS) March Meeting last week. Congratulations! Her abstract is included below.

Epitaxial stabilization of rutile germanium oxide thin film by molecular beam epitaxy

Ultrawide-band-gap (UWBG) semiconductors have tantalizing advantages for power electronics. Materials such as AlN/AlGaN, β-Ga2O3, and diamond have been developed for UWBG semiconducting devices, however, they are still facing challenges, such as doping asymmetry and/or inefficient thermal conduction. Rutile GeO2 (r-GeO2) has been theoretically established to have an UWBG (4.68 eV), high electron and hole mobility (289 cm2 V-1s-1 and 28 cm2 V-1s-1), high thermal conductivity (51 W m–1 K–1) and ambipolar dopability. The synthesis of r-GeO2 thin films has not been reported but is critical to enable microelectronics applications. Here, we report the growth of single-crystalline r-GeO2 thin films on R-plane sapphire substrates using molecular beam epitaxy. We control the competing reactions between the deeply metastable glass phase formation and rutile phase formation as well as absorption and desorption by utilizing (1) a buffer layer with reduced lattice misfit, and (2) the growth condition that allows the condensation of the preoxidized molecular precursor yet provides sufficient adatom mobility. The findings advance the synthesis of single-crystalline films of materials prone to glass formation and provide opportunities to realize promising UWBG semiconductors.

Filed Under: Conferences

Peter has been selected as the 2021 MSE recipient of the Towner Prize for Distinguished Academic Achievement

March 16, 2021 By Matt Webb

The award recognizes the outstanding graduate student in each degree program. Prize criteria include a student’s active participation in research, leadership and academic performance (GPA). 

Congratulations Peter!

Filed Under: Awards

Sieun receives the Rackham Predoctoral Fellowship!

March 16, 2021 By Matt Webb

The Rackham Predoctoral Fellowship supports outstanding doctoral students who are actively working on dissertation research and writing. It seeks to support students working on dissertations that are unusually creative, ambitious and impactful.

Congratulations Sieun!

Filed Under: Awards

New Publication! Interface Transparency and Rashba Spin Torque Enhancement in WSe2 Heterostructures

March 11, 2021 By Matt Webb

Abstract: Rashba spin current generation emerges in heterostructures of ferromagnets and transition metal dichalcogenides (TMDs) due to an interface polarization and associated inversion symmetry breaking. Recent work exploring the synthesis and transfer of epitaxial films on the top of low layer count 2D materials reveals that atomic potentials from the underlying substrate interface are not completely screened. The extension of this transparency effect to other interfacial phenomena, such as the Rashba effect and associated spin torques, has not yet been demonstrated. Here, we report enhanced spin transfer torques from the Rashba spin current in heterostructures of permalloy (Py) and WSe2. We show that insertion of up to two monolayers of WSe2 enhances the spin transfer torques in a Rashba system by up to 3×, without changing the fieldlike Rashba spin−orbit torque (SOT), a measure of interface polarization. Our results indicate that low layer count TMD films can be used as an interfacial “scattering promoter” in heterostructure interfaces without quenching the original polarization.

Full text available from ACS Publications

Filed Under: Publications

Sieun and Nguyen give talks at EMA!

January 26, 2021 By John Heron

Sieun and Nguyen both gave virtual talks at ACerS Electronic Materials and Applications (EMA) last week. Congratulations! Their abstracts are included below.

Sieun’s Abstract: Rutile GeO2: an ultra-wide-band-gap semiconductor for power electronics. Ultra-wide-band-gap (UWBG) semiconductors have tantalizing advantages for power electronics as their wider band gaps enable higher breakdown voltages. A handful of materials such as AlN/AlGaN, -Ga2O3, and diamond have been developed for UWBG semiconducting devices, however, they are still facing numerous challenges, such as doping asymmetry and/or inefficient thermal conduction. In our work, we have identified rutile GeO2 (r-GeO2) to be a promising, yet unexplored UWBG (4.68 eV) semiconductor. Our first-principles calculations predict shallow ionization energies for donors such as Sb, As, and F, a phonon-limited electron mobility of 289 cm2 V-1s-1, and a breakdown electric field of 7.0 MV cm-1, which lead to a higher Baliga figure of merit than -Ga2O3. We also predicted that p-type doping is promising in r-GeO2: the calculated ionization energy for Al acceptors is 0.45 eV and the calculated phonon-limited hole mobility is 27 cm2 V-1s-1. r-GeO2 also has superior thermal conductivity (45 W m–1 K–1 (calculated) and 51 W m–1 K–1 (experiment)) relative to -Ga2O3. Though the thin-film synthesis of r-GeO2 has remained challenging due to its highly metastable amorphous phase, we demonstrate the first synthesis of single crystalline epitaxial thin films of r-GeO2 on a sapphire substrate using ozone-assisted molecular beam epitaxy. Our work motivates further exploration of r-GeO2 as an alternative UWBG semiconductor that can overcome the limitations of the current state-of-the-art UWBG materials.

Nguyen’s abstract: Magnetic properties of thin single crystal Cr2O3 films. Magnetoelectric materials show potential for low-power spintronics via the electric field control of magnetization. Antiferromagnet Cr2O3 is a room temperature magnetoelectric yet the existence of twin domains in thin films grown on metallic electrodes leads to high leakage current and low dielectric breakdown fields. By using an isostructural epitaxial oxide electrode, V2O3, recent studies have shown the possible elimination of these twin domains. Dielectric properties of 200 nm thick films show improved performance, however, for next generation logic and memory the films must be scaled down. Here we present the electrical endurance and magnetic properties of very thin (30-60 nm) single crystal Cr2O3 films grown by pulsed laser deposition onto V2O3 buffered (0001) oriented Al2O3 substrates. A 60 nm single crystal thin film has bulk-like resistivity (1012 Ωcm) and significantly improved breakdown voltage (150-300 MV/m). From magnetometry of a Cr2O3/ferromagnet heterostructure, the blocking temperature is found to be at 285 K, higher than twinned films with similar or greater thickness in literature. Further, Second Harmonic Generation confirms bulk magnetoelectric order of our single crystal thin film at room temperature. These results indicate the importance of crystallinity to realize bulk like properties in very thin films at room temperature.

Filed Under: Conferences

  • « Previous Page
  • 1
  • …
  • 3
  • 4
  • 5
  • 6
  • 7
  • …
  • 19
  • Next Page »

News

  • New Publication! “Composite Spin Hall Conductivity from Non-collinear Antiferromagnetic Order” May 4, 2023
  • New Publication! “Adaptive Magnetoactive Soft Composites for Modular and Reconfigurable Actuators” March 27, 2023
  • New Publication! “Geometric defects induced by strain relaxation in thin film oxide superlattices.” November 10, 2022

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

About

Our work is multidisciplinary. We employ concepts and tools from the fields of materials science, chemistry, physics and electrical engineering to develop new methods to investigate and engineer … Read More

News

New Publication! “Composite Spin Hall Conductivity from Non-collinear Antiferromagnetic Order”

May 4, 2023 By Matt Webb

New Publication! “Adaptive Magnetoactive Soft Composites for Modular and Reconfigurable Actuators”

March 27, 2023 By Matt Webb

Contact

Ferroelectronics Lab
Address: 2030 H.H. Dow

T: (734) 763-6914
E: jtheron@umich.edu
  • Email

Ferroelectronics Lab · Copyright © 2023 · Website by Super Heron Support