Aswathi Sivan
Carrier dynamics in semiconductor nanowires
Institute of Microcroelectronics and Microsystems (CNR Rome)
Semiconductor nanowires are nanostructures with unique optical and electronic properties. These properties offer great promise in their applications in nanoelectronics and nanophotonic devices. Nanowires exhibit several physical properties which are not observed in the bulk. In order to fully utilize the nanowires in device applications one must have a deep understanding of these phenomena.
In this project we investigate the optical properties and carrier dynamics of the semiconductor nanowires using optical techniques. We want to understand the interactions between carriers and phonons inside the nanowires. These interactions take place over a very short temporal range; hence we use ultrafast techniques. We will use techniques like Photoluminescence(PL), Time Resolved PL and Ultrafast Transient Absorption Spectroscopy using Pump- Probe method to study these phenomena. Pump-Probe spectroscopy involves splitting a femto second laser into a pump(stronger) beam and probe (weaker) beam. The pump excites the carriers into a non-equilibrium state. Carrier dynamics can then be measured by observing the pump-induced changes in the transmission/absorption of the probe. The changes in optical properties as a function of time delay between the pump and probe gives us an insight into the electronic relaxation times in the sample. The research will be conducted in the newly built optical laboratory based on a 35 fs amplified Ti:Sa laser system. As the probe we will mainly use the supercontinuum generated in a commercial Femto-second Transient Absorption Spectrometer.
We aim to understand carrier dynamics in nanowires through the study of different systems. First experiments will include charge transfer in ZnO nanowires decorated with CdSe or carbon dots which will be studied using transient absorption curves and the study of the exciton-plasmon interactions in ZnSe nanowires decorated with Ag nanoparticles. Other topics will be the ultrafast carrier dynamics, the band-gap renormalization, and the optical properties of GaAs nanowires and the investigation of In(Ga)As quantum dots embedded in GaAs NWs.
