Transient Grating Spectrum Of Ultrafast Carrier Relaxation In Several Semiconductors

As a typical four-wave mixing technique, transient grating spectroscopy is apowerful tool for probing carrier dynamics in materials. Because of its greatadvantages of high time-resolution and none requirement of morphology and size ofsamples, transient grating spectroscopy is widely used in physical and chemicalresearches to study carrier dynamics in gas, solid, liquid phase materials.Due to the specific electronic and optical properties, graphene has greatpotential to manufacture high-performance computer, nano-scale dielectric devicesand photon transistors, so researches on graphene have attracted more and moreinterests. However, the knowledge of carrier dynamics in graphene is not very clearand the relative theories are not adequate, and then further researches andapplications of graphene are limited. As a typical nonmetal magnetic material, Fe₃O₄is widely used in recording materials, magnetic permeability devices, catalyst andbiomedicine. Especially, researches on Fe₃O₄nanoparticles and Fe₃O₄compositematerials have attracted more and more attentions. Because of the hightime-resolution and the ability to detect the properties of electrons, the carriermobility characteristics of Fe₃O₄and graphene with transient grating technique willbe studied in this thesis.Theory of transient grating is presented firstly. The theoretical formulae ofcarrier mobility, carrier diffusion coefficient and energy level lifetime have beenderived. By building the femtosecond transient grating experimental system withexcitation pulses centered at400nm and800nm, carrier dynamics of Fe₃O₄thinfilms, graphene solution and graphene films have been researched, respectively.Through measuring the intensity of diffracted light at different delay time, therelevant dynamics cures were obtained, and carrier mobility, carrier diffusioncoefficient and energy level lifetime of Fe₃O₄thin films and graphene samples werecalculated and analyzed.