Prof. Teitsworth and members of his research group, May 2010.

1. Dynamics of electric field domains in superlatticesStephen W. Teitsworth, Duke University, DMR 0804232 • We are studying the dynamics of electric field domains and associated charge waves in superlattices (SLs), which consist of alternating layers of different semiconductor materials. Field domains generally degrade the performance of SL-based electronic devices, which have been proposed, for example, as sources of terahertz electromagnetic radiation. • Shunt-enabled field domain suppression – During the past year, we have developed new simulation methods for treating both lateral and vertical charge dynamics in SLs. We have found that the addition of a parallel conductive shunt can stabilize the SL against domain formation provided that the lateral extent Lx of the SL does not exceed a threshold, as illustrated in the three panels on the right side of the image. In the bottom panel, the charge density is nearly uniform and stable, while in the top panel, the charge density undergoes spatio-temporal oscillations. • Huidong Xu et al., Phys. Rev. B 79, 245318 (2009). • H. Xu and S. Teitsworth, Appl. Phys. Lett. 96, 022101 (2010). • Ongoing experiments on SLs precisely measure the statistical properties associated with noise-driven switching dynamics between co-existing field domain configurations. The results of these measurements will be compared with as-yet untested theoretical predictions. Above: schematic depiction of a superlattice with a parallel conductive shunt. Right panels: snapshots of computed electron density (in grayscale) for three structures with slightly different lateral extent, increasing from the bottom to top panel.

2. Dynamics of electric field domains in superlattices Stephen W. Teitsworth, Duke University, DMR 0804232 • Training: During the past year, this project has involved two graduate students (Huidong Xu and Sukrit Sucharitakul), two undergraduate students (Kevin Brown and Adam Kurzrok), one postdoc (Yuriy Bomze), and one visiting international student (Martin Heinrich from the Technical University of Berlin). • Grad student Huidong Xu completed his Ph.D. thesis in April, 2010. • International visitor Martin Heinrich participated in experimental measurements at Duke, the results of which form a part of his Master’s degree thesis. • International collaborations: • The experimental component of this project is enhanced by a collaboration with researchers at the Paul-Drude-Institute for Solid State Electronics (Berlin, Germany), particularly for the growth of superlattice samples. • Some of the simulation methods for theoretical work on shunted SLs were developed in a collaboration with researchers at the Technical University of Berlin. Prof. Teitsworth and members of his research group, May 2010.