Ultrafast Dynamics Of Photoconductivity In Nano Material Lead Sulfide In Terahertz Region

As a semiconductor among IV-VI group,lead sulfide(Pb S)has unique properties such as narrow band gap and large Bohr radius.By tailoring the size of nanostructure,its energy band can be tuned in a wide range between infrared and visible light spectrum,permits it to be applied extensively in photovoltaic materials and infrared detectors.To improve the performance of semiconductor devices,it is crucial to understand the relaxation and transport processes of photogenerated carriers.However,the dynamic processes such as the interaction between free carriers and excitons in Pb S are remain to be researched.Time-resolved terahertz spectroscopy(TRTS)is an ideally non-contact probe for ultrafast dynamics of charge carrier,and it can obtain both frequency and time-resolved photoconductivity information.This thesis explored ways to improve TRTS bandwidth and other performance,and used TRTS to study the ultrafast dynamics of Pb S nanocrystal in Terahertz region,which laid the foundation for the development of Pb S-based optoelectronic devices.The main contents are as follows:(1)A systematic introduction to the composition and experimental modes of time-resolved terahertz spectroscopy,such as terahertz generation,terahertz detection,time-domain spectrum analysis methods,etc.(2)The broadband terahertz emission source based on CoFeB/Pt film was studied,including the relationship between the terahertz amplitude and the pumping optical power,and the verification of the emission mechanism.Using its high bandwidth characteristics,a widespectrum time-resolved terahertz spectroscopy was designed.(3)Using the time-resolved terahertz spectroscopy,the photoconductivity of lead sulfide nanocrystal under different pump-probe time delays was measured,and the Drude-Smith and Drude-Lorenz models were fitted to study the transport characteristics of carriers.Moreover,the influence of pump light intensity on the carrier relaxation rate was detected,and it was found that at higher pump light intensity,Auger recombination participated in the relaxation process of carriers.