Nanostructures are a critical component of innovations in electronics, energy conservation, renewable energy, biomedical research, and health care. We develop and demonstrate metrology techniques to address nanoscale measurement challenges that cannot be met with conventional methods. We synthesize semiconductor nanostructures to serve both as test structures for measurement techniques and as building blocks for novel metrology tools. Much of our work leverages the unique mechanical, optical, and electrical properties of GaN nanowires grown by molecular beam epitaxy, a specialty in which we are one of the leading groups in the world. Recent key projects include the development of superior AFM tips based on nanowires, single-nanowire light-emitting diodes (LEDs), accurate methods for measuring internal quantum efficiency and carrier concentration in semiconductor nanowires, and structural characterization of InGaN quantum wells in GaN nanowires.
Scanning probe metrology using GaN nanowire tips: A major goal of our project is to develop new metrology tools for examining the optoelectronic properties of semiconductor nanostructures. We are currently developing GaN nanowires as multifunctional scanning probe tips, combining light emission, microwave reflection, and topology measurement. The nanowires have been shown to retain their shape indefinitely, thus they are more durable than standard glass near-field scanning optical microscopy (NSOM) tips and more reproducible than state-of-the-art Pt tips for near-field scanning microwave microscopy (NSMM).
Optical measurements of semiconductor nanowires: Using time-resolved photoluminescence (PL) and geometrical variations in nanowires, we demonstrated how to extract a surface recombination velocity. The temperature dependence of the PL lifetime in turn provided a means to measure internal quantum efficiency of GaN nanowires without resorting to inaccurate assumptions about quantum efficiency at low temperature.
Supercontinuum Solar Simulator: By combining a supercontinuum laser with a programmable optical mask, we have developed a new tool to test solar cells under arbitrary and rapidly programmable spectra. The simulator has been applied to a number of photovoltaic materials, including Si, multijunction III-Vs, and thin film CuInGaSe alloys.
Metrology of 3D Nanostructures: Several members of our team are key staff for the Precision Imaging Facility, applying atom probe tomography, transmission electron microscopy, and focused ion beam fabrication to the analysis of nanostructures and thin layers.
High Q Nanoscale Mechanical Resonators: GaN nanowires have unusually low mechanical resonance losses for a nanoscale object. In collaboration with Prof. Charles Rogers at the University of Colorado, we have demonstrated a number of their unique properties and potential applications.
Schematic of GaN nanowire scanning probe tip and void formation around NiAu contact to GaN nanowire.
Start Date:January 1, 1997
Lead Organizational Unit:pml
Source of Extramural Funding:
Mail Stop 815.04