Heterovalent ternary compounds, a new form of semiconductor property engineering: from electronic energy bands to lattice dynamics – Walter Lambrecht

Date: Thu. October 28th, 2010, 4:15 pm-5:15 pm
Location: Rockefeller 301

Over the last five years or so, my group has studied the properties of a new family of nitride semiconductors, the II-IV-N₂, the compounds, such as ZnGeN₂, ZnSiN₂. One can view this as a new way to modify the properties of GaN semiconductors. Instead of isovalent substitution of different group III elements, we substitute alternately a group II and IV element, coordinating each N tetrahedrally with two of each. Unlike isovalent substitution, which leads to disordered alloys, this type of substitution leads to well ordered compounds. Another example, of this type of heterovalent substitution is replacing ZnO by LiGaO₂. These materials have received relatively little attention so far. I will first discuss their lattice dynamics. How do the phonons and related infrared and Raman spectra differ from those of the III-Nitride wurtzite crystals? Their elastic and piezo-electric constants and spontaneous polarization are also compared to those of the III-N semiconductors. Along the way, I will tell you about the density functional perturbation theory that makes these calculations possible. In the second part of the talk, I will discuss their electronic band structure, for which we can now make accurate predictions using the quasiparticle self-consistent GW approach. Finally, I will speculate about their potential for doping, which we intend to study next.