Single gallium nitride nanowire lasers

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Abstract
There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices1,2, including lasers3,4and nonlinear optical frequency converters5. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet–blue light-emitting diodes, lasers and photodetectors6,7. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films8,9. Here we report the observation of ultraviolet–blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry–Perot modes (Q ≈ 103) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV μJ cm−2) supports the idea that the electron–hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet–blue coherent light sources.