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

Peter is off to Los Alamos National Laboratory for several months where he will be working with Aiping Chen at the Center for Integrated Nanotechnologies (CINT) on growth kinetics of entropy stabilized oxides.

Peter was chosen to receive the Graduate Excellence in Materials Science (GEMS) award from the American Ceramic Society (ACerS). Congratulations!

Peter gives a talk on the magnetism of entropy-stabilized oxides at MS&T 2018 in Columbus, OH, entitled Structurally Driven Magnetic Disorder in 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. In the antiferromagnetic entropy-stabilized oxides studied here, we see that by tuning the chemistry, and thus the concentration of local structural distortions, we can either induce or reclaim a large degree of frustration in the magnetic lattice of the material. This effect can then be engineered to enhance the strength of the magnetic exchange field by a factor of 10x in ferromagnetic/antiferromagnetic heterostructures, when compared to a “normal” antiferromagnetic oxide, such as CoO. Our results reveal that the unique characteristics of entropy stabilized materials can be utilized to engineer and enhance magnetic functional phenomena in oxide thin films, as well as offer a powerful platform for the study of defects and functional properties.

Congratulations to Sieun for passing her candidacy exam on September 4th.

Doping is an essential step in semiconductor technology to achieve the desired type and level of electrical conductivity. Thus, predicting both n-type or p-type dopability of a material is a prerequisite to exploit the material for electronic application. First-principles calculations are a powerful tool to understand point-defect properties since experimental studies to identify and characterize defects at the atomic scale are challenging. To predict n-type and p-type dopability of an unexplored wide bandgap material, we investigated the thermal stability and charge state of various intentional dopants, the issues regarding carrier localization, and charge compensation from native defects.