Jun 15, 2007
Enhanced nanowire emitter
Plasmonics provide an elegant technique to enhance or confine electromagnetic energy. A research team at the Naval Research Lab (NRL) used the plasmonic response from a nanotextured silver coating to enhance the transfer of ultraviolet light generated in a group-III nitride nanowire emitter. This is beneficial for optical data storage, spatially resolved chemical imaging, and near-field scanning optical microscopy, as well as a component in hybrid integrated circuits.
An attractive material system for nanowire applications is the group-III nitride semiconductor family, which can be tailored to emit, absorb or transmit light from the UV to the infrared. A vapour–liquid–solid deposition process was developed to grow AlGaN (p-type shell) / GaN (n-type core) nanowires on a Si substrate. The AlGaN sheath enhances the confinement of the optical mode and electrically confines carriers in the GaN quantum wire.
Compared to gold and copper, silver has the lowest absorption and produces the strongest plasmon resonances, particularly in the ultraviolet. Simulations of nanoscale emission and plasmonic-enhanced transfer of emission energy directed the design of the nanowire and metallic coating. This motivated the development of a solvothermal chemistry to deposit a dense packing of silver nanospheres. This nanostructured coating significantly enhanced the plasmonic-based transfer of electromagnetic energy generated in the nanowire to the external near-field.
This overall approach allows direct placement of single or multiple nanowires that can directly couple to a trench dielectric waveguide or metal plasmonic waveguide. Additionally, the NRL team is developing group III-nitride nanowire electronic transistors coupled to these plasmonically enhanced nanowire emitters.
About the author
Michael Mastro is a chemical engineer at the US Naval Research Lab. His research focuses on the fabrication of optoelectronic and high-power electronic devices as well as novel nanostructures.