June 2006

EEEL Demonstrates Wide-Bandgap Semiconductor Nanowire Technology

Researchers in the Optoelectronics Division of EEEL have grown gallium nitride nanowires with superior crystalline quality and have demonstrated prototype electronic and optoelectronic devices. The isolated nanowires, 50-500 nm in diameter and up to 8 micrometers long, were grown by molecular beam epitaxy without the use of metal catalysts. NIST is one of only a few groups in the field to have demonstrated this growth capability. Unlike epitaxial thin-film gallium nitride and bulk crystals, the nanowires are free of dislocation defects and fully relaxed to bulk lattice parameters, as verified by transmission electron beam diffraction and x-ray diffraction. High luminescence output compared to bulk gallium nitride confirms the high crystalline quality and chemical purity. The nanowires enabled the first room-temperature measurement of unambiguous photoluminescence polarization anisotropy in unstrained wurtzite gallium nitride that arises from the symmetry of the material. These measurements are difficult to perform in typical thin-film gallium nitride or quasi-bulk free-standing platelets of the material but are readily enabled by the natural geometry offered by the nanowires.

The NIST team has fabricated a number of prototype nanowire structures and devices. They include a nanowire-based light-emitting diode operating at an ultraviolet center wavelength of 385 nm, a single-nanowire field-effect transistor (FET), quantum wells embedded in nanowires, and air-bridge cantilevers. A number of collaborators are involved in the project, including characterization work in MSEL and by a manufacturer of commercial gallium arsenide FETs.

Nanowire UV-visible lasers are being pursued for applications spanning high resolution (spatial and spectral) spectroscopy for fundamental material studies, narrow line UV lasers for quantum information science, detection of chemical and biological threats, and cancer therapy and diagnosis. Since nitride nanowires are structurally robust and electrically, mechanically, and optically functional, they enable further applications as nanowire resonators, actuators, NEMS, and in-cell biological sensors.

Contact: Bob Hickernell, 303-497-3455 (Boulder)