Modeling and Fabrication of Nanowire Lasers

Semiconductor NWs are of both large fundamental and technological interest and have generated enormous interest worldwide in the past few years. These free-standing NWs are usually obtained by epitaxial growth on semiconductor surfaces with predeposited m etal nanoparticles. The NW diameter is fixed by the size of the metal particles but typical sizes range in the order from 10 nm to 100 nm in diameter with a few micrometers in length depending on growth conditions. Key challenges in NW research today are related to all aspects from understanding the detailed growth mechanism to more applied challenges like how to assemble and address NWs into more advanced circuitry. In order to get reproducible NW interfaces, detailed understanding of both the chemistry and physics occurring at the interface will be very important. As important will it be that one can precisely control NW orientation, purity, size uniformity, dimensionality, alloy compositions, doping density and distribution. For NW lasers it will be e specially important to reduce non-radiative defects, precisely control dopant distribution and to make low-resistive ohmic contacts. Although the first electrically injected NW laser has already been demonstrated (in Prof. Liebers laboratory at Harvard in 2002), the performance of this first NW laser with a threshold current of 200 uA was far from impressive. Considering the fact that vertical cavity surface emitting lasers (VCSELs) have shown similar threshold currents with almost three orders of magnitu de larger material volume (2 um diameter VCSEL cavity), it should be possible to produce NW lasers with sub-uA threshold currents in the future. This will, however, require very detailed NW laser modeling as well as advancements in the NW growth and proce ssing to reach such performance levels. With this research project we would like to address some of these important issues in order to make some significant advances from present state-of-the-art NW lasers.