Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

New Publication:! “Rutile GeO2: An ultrawide-band-gap semiconductor with ambipolar doping”

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New Publication! S. Chae, , J. Lee, K. A. Mengle, J. T. Heron, and E. Kioupakis Appl. Phys. Lett. 114, 102104 (2019)

Abstract: Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with the increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with the increasing bandgap and significantly limit the semiconductor devices that can currently be realized. Using hybrid density functional theory, we demonstrate rutile germanium oxide (r-GeO2) to be an alternative UWBG (4.68 eV) material that can be ambipolarly doped. We identify SbGe, AsGe, and FO as possible donors with low ionization energies and propose growth conditions to avoid charge compensation by deep acceptors such as VGe and NO. On the other hand, acceptors such as AlGe have relatively large ionization energies (0.45 eV) due to the formation of localized hole polarons and are likely to be passivated by VO, Gei, and self-interstitials. Yet, we find that the co-incorporation of AlGe with interstitial H can increase the solubility limit of Al and enable hole conduction in the impurity band. Our results show that r-GeO2 is a promising UWBG semiconductor that can overcome current doping challenges and enable the next generation of power electronics devices.

Full text available from Applied Physics Letters

Sieun wins Barbour Centennial Award

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Established in 2017 to honor 100 years of one of the University’s oldest and most prestigious scholarships, the Barbour Centennial Award helps graduate student research via financial support for travel, resources, and living expenses. Barbour Scholar alumnae from across the globe came together to contribute to this gift. 

Peter and Sieun give talks at EMA 2019

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This past week, both Sieun and Peter gave talks at the annual American Ceramic Society Electronic materials and applications (EMA) conference on defect formation and magnetic disorder in entropy stabilized oxides.

Defect and disorder driven dielectric properties of entropy-stabilized oxides.

Abstract: Entropy-stabilized oxides (ESO) are a solid solution of five or more binary oxides in a single lattice, stabilized by the large configurational entropy from cationic disorder. Due to their tunable chemical heterogeneity and intrinsic disorder, ESO are expected to demonstrate novel functional behavior. Point defects in oxides, however, can have a strong influence on functional properties, yet an understanding of point defects in ESO is unknown. Here we present on a theoretical and experimental investigation of point defects and disorder in (MgCoNiCuZn)O-based ESO using density functional theory (DFT) and dielectric measurements. We theoretically predicted that the thermodynamic stability of vacancies in ESO strongly depends on their nearest-neighbor configuration, indicating that the types and concentrations of defects can be tuned by the composition of cations, particularly Cu. Our calculated dielectric constant varies depending on vacancy and cation composition. To experimentally characterize these materials, we have integrated single crystalline entropy-stabilized oxide thin films into vertical capacitor devices by using MgO/SrTiO3 buffered conductive Si substrates and performed dielectric testing over a wide range of frequencies. We varied the composition of the films and observed the effect of local lattice distortion that arises from the composition of Cu on the dielectric behavior of ESO.

Magnetic Frustration Engineering Through Stereochemical Disorder in Single Crystalline Entropy-Stabilized Oxides

Abstract: A unique benefit to entropic stabilization is the increased solubility of elements, which opens a broad compositional space with subsequent local chemical and structural disorder resulting from different atomic sizes and preferred coordinations of the constituents. It is unknown, however, to what degree this structural disorder contributes to material functionalities. In the antiferromagnetic entropy-stabilized oxides studied here, we see that by tuning the concentration of local structural frustrations caused by Jahn-Teller active cations, we induce or reclaim a large degree of disorder in the magnetic lattice of the material. This effect can be utilized to tune the anisotropy and magnetic structure of the oxide to approach that of an isotropic spin glass, yet still in a single crystalline material. Our results reveal that the unique characteristics of entropy stabilized materials can be utilized to realize novel magnetism in oxide thin films.


New Publication! “Point defects and dopants of boron arsenide from first-principles calculations: Donor compensation and doping asymmetry”

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New Publication! S. Chae, K. Mengle, J. T. Heron & E. Kioupakis Appl. Phys. Lett. 113, 212101 (2018)

Abstract: We apply hybrid density functional theory calculations to identify the formation energies and thermodynamic charge transition levels of native point defects, common impurities, and shallow dopants in BAs. We find that AsB antisites, boron-related defects such as VB, BAs, and Bi-VB complexes, and antisite pairs are the dominant intrinsic defects. Native BAs is expected to exhibit p-type conduction due to the acceptor-type characteristics of VB and BAs. Among the common impurities we explored, we found that C substitutional defects and H interstitials have relatively low formation energies and are likely to contribute free holes. Interstitial hydrogen is surprisingly also found to be stable in the neutral charge state. BeB, SiAs, and GeAs are predicted to be excellent shallow acceptors with low ionization energy (<0.03 eV) and negligible compensation by other point defects considered here. On the other hand, donors such as SeAs, TeAs SiB, and GeB have a relatively large ionization energy (∼0.15 eV) and are likely to be passivated by native defects such as BAs and VB, as well as CAs, Hi, and HB. The hole and electron doping asymmetry originates from the heavy effective mass of the conduction band due to its boron orbital character, as well as from boron-related intrinsic defects that compensate donors.

Full text available from Applied Physics Letters

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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

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Ferroelectronics Lab
Address: 2030 H.H. Dow

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