The UM College of Engineering newsletter has just published an article on our recent publication, “Magnetic frustration control through tunable stereochemically-driven disorder in entropy-stabilized oxides.”

Read the full article at The Michigan Engineer News Center.

Entropy-stabilized oxides possess a large configurational entropy that allows for the unique ability to include typically immiscible concentrations of species in different configurations. Particularly in oxides, where the physical behavior is strongly correlated to stereochemistry and electronic structure, entropic stabilization creates a unique platform to tailor the interplay of extreme structural and chemical disorder to realize unprecedented functionalities. Here, we control stereochemically driven structural disorder in single crystalline, rocksalt, (MgCoNiCuZn)O-type entropy-stabilized oxides through the incorporation of Cu2+ cations. We harness the disorder to tune the degree of glassiness in the antiferromagnetic structure. Structural distortions driven by the Jahn-Teller effect lead to a difference in valence on the Co cation sites, which extends to dilution and disorder of the magnetic lattice. A spin glass model reveals that the fractional spin ordering of the magnetic lattice can be tuned by ∼65%. These findings demonstrate entropy-stabilization as a tool for control of functional phenomena.

Full text available from Physical Review Materials

“Today, materials scientists and engineers play a critical role in the technological evolution of our society, from using advanced computational modeling to guide the development of lighter and stronger metal alloys, to synthesizing self-assembled nanostructures for energy efficient optoelectronics. The trouble is, unlike mechanical or electrical engineering, students are usually not exposed to materials science until well into higher education, and oftentimes never truly learn what it is.
Since 2017, UM materials science graduate students have been teaming up with engineering diversity and educational outreach experts, physical science education specialists, museum curators, and local teachers to develop and implement materials science curriculum and demonstrations targeting K-12 classes.”

full text available from Bulletin of the American Ceramic Society

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 Sb_Ge, As_Ge, and F_O as possible donors with low ionization energies and propose growth conditions to avoid charge compensation by deep acceptors such as V_Ge and N_O. On the other hand, acceptors such as Al_Ge have relatively large ionization energies (0.45 eV) due to the formation of localized hole polarons and are likely to be passivated by V_O, Ge_i, and self-interstitials. Yet, we find that the co-incorporation of Al_Ge 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

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