Keywords: one-dimensional nanostructure, quantum wire lasers, nanowire, semi-conductor laser, quantum confinement, nanotechnology, nanolasers
Nanolasers: lasing from nanoscale quantum wires
Semiconductor lasers are in many ways second only to transistors as to their impact on today's high-tech industries. The unique characteristics, such as narrow emission wavelength, high frequency modulation, and device integratibility, make semiconductor lasers ideal photon sources for applications as diverse as telecommunication, signal processing, material characterisation, and medical diagnostics. Advances in material growth technologies, particularly molecular beam epitaxy, metal-organic chemical vapor deposition, and a suite of chemical synthesis techniques, make the fabrication of high quality nanometer scale semiconductor structures possible. Thanks to the quantum size effects that drastically modify the energy spectra of confined electrons in reduced dimensions, the population inversion necessary for lasing action occurs more efficiently as the active semiconductor gain medium is scaled down from the bulk to the nanometer scale. Consequently, semiconductor lasers built with nanoscale active media are expected to exhibit extraordinary features such as great color range, high optical gain, and low lasing threshold. Indeed, miniaturised lasers using nanoscale semiconductor gain media - two-dimensional quantum wells, one-dimensional quantum wires, and zero-dimensional quantum dots - have shown significant improvements in device performance. This article provides an overview of the physics and technologies behind the rapid progress of miniaturisation of semiconductor lasers, in particular the quantum wire lasers based on one-dimensional nanoscale optical gain media. Since the first report of lasing in quantum wires by Kapon and his co-workers, quantum wire lasers have evolved from "microlasers" in which the one-dimensional nanostructure is embedded in a micron size optical cavity, to "nanolasers" in which, as we recently demonstrated, the material gain and optical feedback are simultaneously achieved by individual nanoscale quantum wires. One-dimensional semiconductor fabrication technologies based on nanoscale lithography, self-organisation, selective growth, and chemical synthesis will be reviewed along with recent advances of quantum wire lasers built upon each of these fabrication technologies.