Semiconductor Nanowire Lasers

Semiconductor nanowires can function as both gain medium and optical cavity, and thus represent a unique class of miniaturized laser sources for the assembly of nanoscale photonic systems. In this talk we will review the rational design and synthesis of nanowires and nanowire heterostructures as laser sources, describe how their structure design interplays with optical properties, and discuss exciting device applications. Group III-nitride nanowire structures will be used as a model system to illustrate our approach towards nanowire lasers. First, the general synthetic strategy for rational growth of semiconductor nanowires and the underlying physical mechanism of lasing in these materials will be reviewed. Second, structural characterization and photoluminescence studies of homogeneous GaN nanowires will be discussed. These studies will illuminate how basic structural characteristics affect threshold for ultraviolet room-temperature lasing in these homogeneous structures. Third, multicolor nanowire lasers based on InGaN multi-quantum well (MQW) radial nanowire heterostructures will be described. Cross-sectional transmission electron microscopy studies allow direct visualization of well-defined internal interfaces and demonstrate our ability to control quantum well growth down to atomic level. These functional nanowire structures were optically pumped individually to lasing from 380 to 494 nm at room temperature, depending on the alloy composition of MQWs. Key factors contributing to the lasing threshold were evaluated by three-dimensional finite-difference time-domain calculations. Last, current injection schemes for electrically-driven nanowire light-emitting diodes/lasers with the emphasis on n-GaN/InGaN MQW/p-AlGaN/p-GaN radial nanowire heterostructures will be discussed.