PHOTONICS
Rather than engineering the electronic band structure, as in QCL research, one can modify the photonic band structure of a material by engineering its optical properties (e.g. creating a periodic array of holes within an optical medium). Such structures can be studied on their own or incorporated into QCLs, microfluidic sensors, etc. Our group has also done extensive research with semiconductor nanowires both exploring fundamental aspects of their photonic and optoelectronic properties as well as applications.
Laser action in nanowires
Using the highest quality material, we are studying the parameters that control laser oscillation at the nanoscale in semiconductor nanowires. In particular, we were able to provide the first conclusive demonstration of laser oscillation in nanowires by systematically studying the transition from amplified spontaneous emission (ASE) to laser action. Furthermore, our work points to a key dependence of laser threshold on the nanowire diameter, a feature that has been largely overlooked in previous work.Mariano Zimmler in collaboration with the group of Carsten Ronning at the University of Jena, Germany.
Scalable fabrication of nanowire photonic and electronic circuits
The field of semiconductor nanowires has witnessed rapid growth in recent years due to the development of inexpensive methods for their synthesis in large quantities. However, practical circuits necessitate the development of techniques for assembling nanowire devices in a highly parallel, scalable, and reproducible manner over large areas. Our group has developed such a technique based on spin-on glass technology and standard photolithography, which makes it possible to contact nanowires simultaneously over entire silicon wafers for electronic and photonic applications.Mariano Zimmler in collaboration with the group of Carsten Ronning at the University of Jena, Germany.
Single nanowire optoelectronics
Our group is also working to develop a detailed understanding of the physics behind the operation of the simplest nanowire light-emitting devices. We are concentrating on a ''sandwhich'' geometry in which a nanowire is placed between a heavily doped substrate and a top metallic electrode, using an insulating spacer layer (cross-linked PMMA or HSQ) to prevent the metal electrode from shorting to the substrate. This structure offers many advantages over alternative LED geometries. Furthermore, due to the non-ideality of the nanowire-substrate junction, new interesting physics arise. For example, if we use a silicon substrate and a gallium nitride nanowire, both of n-type, we can selectively obtain luminescence from either the nanowire (ultraviolet) or the substrate (infrared) simply by reversing the polarity of the applied voltage.Mariano Zimmler in collaboration with the group of Venkatesh Narayanamurti at Harvard University.
PAST PROJECTS
Optical Evanescent Wave Bonding
We are working to observe mechanical deflections in freestanding waveguides that result from evanescent light coming from a nearby waveguide, as well as the evanescent fields of the deflecting waveguide. Our calculations indicate that these waveguide deflections can be attractive (two waveguides bend towards each other) or repulsive (two waveguides bend away from each other) depending on the relative phase of the light in the two waveguides. These attractive and repulsive states are analogous to molecular binding and anti-binding states.Jenny Smythe in collaboration with Marko Loncar (Harvard), John Joannopoulos, Steve Johnson and Mihai Ibanescu (MIT), and Axel Scherer, Michael Hochberg, and Guangxi Wang (Caltech)