Ultrafast Carrier Dynamics Of Cuprous Oxide Films

Cuprous oxide,as a p-type direct bandgap semiconductor material,has a bandgap between 1.8 e V and 2.3 e V,can directly absorb visible light,and is rich in mineral resources,low in cost and low in toxicity,so it has a great application prospect.Nowadays,with the development of semiconductor material preparation technology,various micro shapes,sizes and forms of cuprous oxide materials have been prepared.Cuprous oxide has many new optical properties,and has been widely used in photocatalysis,solar cells,lithium-ion batteries,fluorescent probes,sensors and photodetectors.Therefore,it is of great significance to study the photogenerated carrier process of cuprous oxide and understand its internal photophysical mechanism for the application of cuprous oxide in the above aspects and the design of small microelectronic devices with faster response and faster information processing in the future.The study of ultrafast dynamics by means of pump probe technology,which uses the relative delay of two beams in space to achieve high temporal resolution,is a relatively simple and practical technology to explore the ultrafast process and mechanism.In this paper,femtosecond pump probe technique is used to investigate the ultrafast carrier dynamics of cuprous oxide thin films,and the process and time constant of photogenerated carrier ultrafast dynamics of cuprous oxide thin films are analyzed by double exponential fitting.The specific contents of this paper are as follows:1.Research background.Firstly,the development,characteristics and application of femtosecond laser technology are introduced;Then,the time-resolved spectroscopy techniques used to measure ultrafast processes are briefly introduced,including optical Kerr gate technique,streak camera technique,fluorescence up conversion technique,time-dependent single photon counting technique,pump probe technique and transient absorption technique;Finally,the basic properties,preparation methods and applications of cuprous oxide are described in detail.2.Theoretical analysis and experimental methods.Firstly,the semiconductor carrier dynamics is introduced;Then the ultrafast dynamics process of semiconductor photogenerated carriers is introduced in detail,including carrier excitation,carrier scattering and carrier recombination;Finally,the measurement method pump probe technology used in this paper is described in detail,including the characteristics,classification and theoretical model of pump probe technology.3.Preparation and characterization of cuprous oxide films.Cuprous oxide thin films were prepared by RF magnetron sputtering;X-ray diffraction,scanning electron microscopy,ultraviolet visible near infrared spectrophotometer and energy dispersive X-ray spectrometer were used to characterize the crystal structure,surface morphology,thickness and transmission spectrum of cuprous oxide thin films;The band gap energy of cuprous oxide is obtained by linear extrapolation.4.Ultrafast carrier dynamics of cuprous oxide films.The ultrafast carrier dynamics of cuprous oxide film excited by single photon is studied.Two decay processes are obtained by fitting,one is the carrier scattering process with faster time scale,and the other is the carrier recombination process with slower time scale.Then the ultrafast carrier dynamics of cuprous oxide film under two-photon excitation is studied.A faster time scale carrier scattering and a slower time scale carrier recombination are also obtained.Compared with the single photon excitation,the twophoton excitation takes a longer time to scatter the streamer,because the two-photon absorption produces fewer carriers than the single photon absorption,and the carrier concentration is low,so the scattering rate is slow.Finally,the ultrafast carrier dynamics of cuprous oxide thin films excited by two-photon with short probe wavelength is studied,and the ground state bleaching phenomenon caused by carrier saturation absorption is observed.