Using Ultrafast Optical Spectroscopy to Unravel Fundamental Properties of One-and-Two-Dimensional Nanostructures

January 30, 2015

Rohit Prasankumar

Low-dimensional nanostructures have attracted much interest in recent years due to their vast potential for applications in areas ranging from medicine to solar energy.  Many of these applications depend critically on a detailed knowledge of the optical and electronic properties of these nanosystems and their temporal evolution after a perturbation to the system.  Ultrafast optical spectroscopy has attained prominence due to its ability to resolve dynamics in conventional metals and semiconductors at the fundamental time scales of electron and lattice motion.  Therefore, the ability to probe the dynamic response of low-dimensional nanostructures after ultrafast excitation stands to reveal a great deal of information that will increase understanding of their basic physics and aid in their optimization for a variety of applications. In this talk, I will discuss our recent measurements of carrier dynamics in one-and two-dimensional semiconductor nanostructures, which enable us to not only gain insight into their dynamical properties, but also to shed light on their intrinsic material properties.  Our group has an ongoing focus on ultrafast carrier dynamics in quasi-1D semiconductor nanowires, where we have performed spatiotemporally resolved ultrafast optical microscopy to map carrier dynamics in single Si and GaN heterostructured nanowires.  We have also performed ultrafast optical measurements on the 2D transition metal dichalcogenide MoS2, which has attracted much recent interest due to its potential for photonic applications. Finally, we have recently established the capability to perform terahertz (THz) magneto-optical spectroscopy in magnetic fields up to 8 T and used this to perform the first THz measurements of the cyclotron resonance in two-dimensional hole gases. These experiments provide fundamental insight into carrier relaxation and transport in these novel systems, revealing information critical to optimizing their performance for applications in photovoltaics, mode-locked lasing, thermoelectrics, and solid-state lighting