  We review principles and trends in the use of semiconductor nanowires (NWs)
as gain media for stimulated emission and lasing. Semiconductor nanowires have
recently been widely studied for use in integrated optoelectronic devices, such
as LEDs, solar cells, and transistors. Intensive research has also been
conducted on the use of nanowires for sub-wavelength laser systems that take
advantage of their quasi-one-dimensional nature, flexibility in material choice
and combination, and intrinsic optoelectronic properties. First, we provide an
overview on using quasi-one-dimensional nanowire systems to realize
sub-wavelength lasers with efficient, directional, and low-threshold emission.
We then describe the state-of-the-art for nanowire lasers in terms of
materials, geometry, and wavelength tunability. Next, we present the basics of
lasing in semiconductor nanowires, define the key parameters for stimulated
emission, and introduce the properties of nanowires. We then review advanced
nanowire laser designs from the literature. Finally, we present interesting
perspectives for low-threshold nanoscale light sources and optical
interconnects. We intend to illustrate the potential of nanolasers in many
applications, such as nanophotonic devices that integrate electronics and
photonics for next-generation optoelectronic devices. For instance, these
building blocks for nanoscale photonics can be used for data storage and
biomedical applications when coupled to on-chip characterization tools. These
nanoscale monochromatic laser light sources promise breakthroughs in
nanophotonics, as they can operate at room temperature, potentially be
electrically driven, and yield a better understanding of intrinsic nanomaterial
properties and surface state effects in low-dimensional semiconductor systems.
