Nanofabrication of tunable nanowire lasers via electron and ion-beam based techniques.

GaN nanowires were created from planar GaN epilayers using a top-down fabrication technique consisting of a dry etch followed by an anisotropic wet etch. The GaN nanowires are m-plane bounded with tightly-controlled dimensions. Single-mode lasing was achieved with GaN nanowire with 130 nm diameter and 5 μm length. Numerical simulations based on a multimode laser theory indicate that the suppression of transverse and longitudinal side-modes is caused by strong mode competition and narrow gain bandwidth. For multiple mode GaN nanowire lasers with large diameter, we demonstrated that coupled nanowire pairs provide a mode selection mechanism through Vernier effect and become single mode lasers. Moreover, transverse-mode suppression and single-mode lasing is demonstrated in GaN nanowires in contact with gold substrates, which introduces an attenuation effect to the cavity modes. The finite-difference timedomain simulations confirm the absorption effect, which give rise to a mode selection mechanism for realizing single mode operation.