When 3:30 PM - 5:00 PM Mar 01, 2013
Where 1670 Beyster Building
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Heterovalent ternary compound semiconductor nitrides, II-IV-N2, a new paradigm in band structure engineering


Walter Lambrecht
Department of Physics, Case Western Reserve University

The  usual method for band structure engineering in semiconductors is to make isovalent alloys: e.g. In_xGa_(1-x)N. Here we consider heterovalent mixing: e.g. replacing the group III by a group II and group IV atom, such as GaN ->ZnGeN2. While this substitution is  well-known in other III-V compounds to lead to chalcopyrite structures, it can also be done for wurzite based structures such as nitrides. In the past 7 years, we have extensively studied the properties of II-IV-N2 semiconductors as well as a I-III-O2 (namely LiGaO2) which one can view as a cousin of ZnO. In this talk I will discuss their lattice dynamics and electronic structure. The phonon spectra are significantly more complex than one couldexpect based on band folding ideas. Elastic constants, piezo electric properties and spontaneous polarizations  were also investigated. Comparisons with the limited available experimental data will be discussed. The electronic band structures were determined using the quasiparticle self-consistent GW method. The Kohn-Luttinger effective Hamiltonian was generalized to describe the dispersion and splittings of the valence band in these lower symmetry crystals and the corresponding parameters were determined. I will briefly describe the advances in computational methods which make these calculations possible. Finally, we discuss the prospects of doping of this new class of semiconductors.

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