Photoluminescence Spectroscopy Applied to Semiconducting Nanowires: A Valuable Probe for Assessing Lattice Defects, Crystal Structures, and Carriers' Temperature

Photoluminescence (PL) spectroscopy is a reliable, non-invasive tool widely employed to investigate the electronic properties of semiconductors and their nanostructures near the band-gap edge states. PL is particularly relevant for determining the energy and symmetry properties of excitons as well as the nature and relative abundances of defects in a semiconductor material. In this chapter, we will present PL measurements on InP nanowires (NWs), a notable material system for NW structures. We address the electronic and defect properties of wurtzite NWs, and provide a comparison with the zincblende counterpart. PL as a function of various external parameters, such as photoexcited carrier density and temperature, allows us to assign the origin of various recombination bands typically observed in InP NWs grown by selective area epitaxy or by vapor--liquid--solid method. The possibility to explore the density of states of NWs is implemented by PL-excitation measurements as a function of polarization, which unveil the optical selection rules pertinent to the wurtzite crystal phase. Finally, a careful analysis of the PL lineshape provides also access to carriers' temperature and thus precious insight on carrier relaxation phenomena that occur in thin NWs.