Bio-Templated Materials and Devices

Driven by scaling requirements and the pursuit of novel material properties, nanotechnology has advanced rapidly. Given the shortcomings of man-made tools for precise nanoscale assembly, many researchers have looked to biology for inspiration. The natural world uses biomolecules such as peptides and proteins to expertly direct the assembly of inorganic materials. The organic-inorganic interface controls assembly on multiple length scales ranging from nanoscale to microscale depending on the required function. Researchers have begun to harness this extraordinary capability to make a variety of devices by integrating peptides or proteins which are able to bind technologically significant materials into the structural proteins of viruses. The approach has allowed the realization of unique device geometries, as well as the opportunity for enhanced performance and functionality. Current efforts in our lab are focused on using biomolecules to synthesize new, multi-component nanoscale materials to address challenges in the area of solar power generation, photocatalysis, and gas sensing.

WidE BandGap Optical Resonators

Micro- and nano- optical resonators such as microdisks and photonic crystal cavities, have enabled the observation of important optical phenomena including modified spontaneous emission rates, high quality factors, extremely low modal volumes, directional emission, and low threshold lasing. The compact geometry of these resonators is advantageous for high-density integration with filters and waveguides into optical circuits. III-nitride semiconductors and other wide bandgap materials are used to form active, short wavelength resonators which emit from ultraviolet to green. Our lab is interested in the design and fabrication of novel micro- and nano- cavities with emphasis on low threshold and sensing applications.

Photoelectrochemical and Etching Processes

Photoelectrochemical (PEC) etching is a light-induced etching technique which uses photogenerated minority carriers to facilitate material dissolution. A semiconductor anode and Pt counter electrode immersed in an electrolyte solution form an electrochemical cell which is illuminated with above bandgap light. In the presence of sufficient photogenerated carriers, etching occurs at the semiconductor/electrolyte interface. Minority carrier transport to the semiconductor surface is determined by the energy band bending at the semiconductor/electrolyte interface which can be readily engineered by choice of material or dopant, or through an externally applied bias. Most commonly, the anode is an n-type semiconductor in which photogenerated holes at the semiconductor/electrolyte interface enable dissociation of the semiconductor through the formation of an oxide which is soluble in the electrolyte or through direct ionic dissolution of the semiconductor. PEC etching is a low damage etching approach which is both material- (dopant and bandgap) and spatially-selective. Furthermore, it can be used for highly anisotropic vertical etching in addition to deep lateral undercut formation. It is a particularly attractive technique for semiconductor materials such as the III-nitrides in which conventional electrochemical etchants are relatively ineffective.

Dry etching processes such as reactive ion etching (RIE), inductively-coupled plasma (ICP) etching, and chemically-assisted ion beam etching (CAIBE) use low energy ion bombardment to attain anisotropic etch profiles. Low energy ions can damage semiconductor materials, degrading device performance. We are interested in studying the range and effect of ion damage on electrical and optical materials properties.