Jeffrey Shainline
Doctoral Researcher
Department of Physics
| phone | (401) 863-3010 |
| fax | (401) 863-3930 |
| jeffrey_shainline@brown.edu |
Current Research Interests
My research is focused mainly on silicon nanophotonics. I am interested in investigating methods by which modifying silicon on the nanoscale can lead to enhanced optical properties. While silicon is the medium for most of my experiments, the physical understanding can be applied to many other semiconductors. The focii of my research are illustrated below.
•Utilizing defects for optical gain
Photoluminescence (PL) spectrum (semilog and linear) comparing the G line from C-rich SOI and plain SOI.
Schematic of the G center responsible for the G line above. See also the work by Song et al..
I have been working with Efi Rotem as he has led our group's recent study of the optical properties of carbon-rich silicon. By solid phase epitaxial regrowth we have fabricated silicon with amounts of carbon exceeding by orders of magnitude that allowed by the solid solubility of C in Si. Using this technique, an increase in the G line from nanopatterned Si by a factor of 33 was observed.
•Periodic structures with complex dielectric functions, especially highly ordered periodic gain arrays
The nanopatterned C-enriched SOI sample which gave the PL spectrum shown above
Etching pores in Si through an anodized aluminum oxide (AAO) membrane has been shown to create G centers. Introducing G centers with this nanopatterning technique results gives rise to very thin layers of gain material surrounding the nanopore walls. These regions of the crystal are rich with G centers and therefore give rise to gain. The resultant system is a periodic array with hexagonal symmetry containing regions characterized by three different dielectric functions: that of bulk Si, that of the G-center-rich gain medium, and that of vacuum. The photonic crystal aspects of this are interesting. There is potential to mold the photonic band structure and the local density of optical states (LDOS). Future research in our lab will explore the optical properties of this structure.
•Silicon nanostructures including nanopatterned silicon-on-insulator as a lasing medium
Schematic of an optically-pumped thin silicon film containing an array of nanopores with G centers embedded in the pore walls
The nanopatterned Si structure has several features which make it prime for optical activity. The damage which is inflicted to the lattice is contained in a small volume near the pore walls, leaving the majority of the crystal pristine. Excitons created in the bulk enjoy the long life characteristic of indirect gap semiconductors. This is as opposed to systems where optically active centers are created throughout the crystal via ion bombardment, a technique which leads to very lossy materials. Additionally, the reduced electronic screening near the pore walls leads to a reduced exciton binding energy. Also, the removal of material that occurs at the pore walls leads to strain in the lattice. While this strain is difficult to quantify, TEM analysis indicates that the strain is compressive, which lead to band gap narrowing near the pore walls. This narrowing would be another factor that would decrease the exciton binding energy locally. The spatial energy gradient experienced by excitons would lead to a force on the quasiparticle (in a semiclassical manner of speaking) drawing the excitons from the pristine crystal away from the pores where they are long-lived toward the pore walls where they are likely to recombine radiatively through G centers. It is a complicated physical system with many physical elements that are difficult to decouple. Can we devise ways to decouple the physical elements in order to study them independently with the goal of finally recoupling the various physical elements in order to make Si optoelectronic devices?
•Metamaterials and unique properties arising from coupling between metallic and semiconducting media
SOI nanopores filled with gold
Studying semiconductors coupled to metallic media is interesting for a number of reasons. One is that the near-field enhancements of metallic particles can increase absorption by the semiconductor. In our case, we have fabricated nanopatterned silicon structures wherein the pore walls are rich with optically-active G centers. By filling the pores with a metal with a strong plasmonic resonance we hope to get large near-field enhancements. Since the G-center-rich regions of the material are the within the near-field radius of the metallic particles, we hope to achieve efficient pumping of the centers. Another interesting facet of this type of coupling is the effect surface plasmons can have on spontaneous emission. By increasing coupling to radiation modes, surface plasmons can enhance extraction efficiency (see Sun et al. (2007)). So, there you have interesting features regarding population of and emission from optically active states. But there's more. Perhaps the most interesting aspects of this system have to do with cavity QED properties (see the epic hexology by Agarwal: I. II. III. IV. V. VI. ). With the parameters of pore radius, interpore spacing and contrast of dielectric functions one can tune the local density of optical states (LDOS) (also check out the work on LDOS by Fussell et al.). This may also be useful of enhancing light extraction, gain localization or modification of selection rules (if you are interested in modification of selection rules talk to Rashid Zia).
Education
•Ph.D. candidate in Physics (8/2005 - ), Brown University
•B.A. in Physics (8/2000 – 5/2005), University of Colorado, Boulder
Publications
Siegert Pseudostates: Completeness and Time Evolution, Santra et al. Phys. Rev. A 71 032703 (2005).
Conference Proceedings
Additional Information
Would you like to read my undergraduate honors thesis?
Perhaps you'd like to visit my personal webpage at www.matildamundane.net.