US researchers have observed lasing in gallium nitride (GaN) nanowires for the first time. The team from the University of California says that its tiny UV-emitting lasers may find uses in lab-on-a-chip systems and in high-density data storage.

"This research is an extension of our work on ZnO nanowire lasers," researcher Peidong Yang told Optics.org. "The GaN devices typically have a cross-section in the 100-nm region. Previous devices are all essentially two-dimensional whilst these nanowire lasers are one-dimensional."

GaN is a wide-bandgap semiconductor that forms the basis of all UV-emitting LEDs and laser diodes. Emission from nanowire structures has remained elusive but now, thanks to advances in microfabrication techniques, the team has seen emission in both GaN nanowires and films.

To stimulate lasing, the GaN nanowires are optically pumped by the fourth harmonic of a pulsed optical parametric amplifier (290 to 400 nm). This excitation produces a plasma of holes and electrons in the nanowire, which then recombine across the bandgap to produce UV photons with wavelengths between 360 and 400 nm.

"The nanowire itself serves as a Fabry-Perot cavity and a gain medium for light amplification," explained Yang. "The ends of the wire act as mirrors to provide the feedback for stimulated emission".

Yang and colleagues used microscopy to characterize the laser modes. According to Yang, bright emission at the end of the wire shows strong waveguiding behaviour and that the cavity modes are Fabry-Perot rather than whispering gallery modes.

"As the excitation energy increases, we also see a strong redshift in the emitted wavelength," said Yang. "This supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature."

Yang says that the next step in the research is to make an electron-injected version of the laser. "This would essentially be a laser diode based on nanowires," he says. "We are actively working on this just now."