Study On Light Induced Transverse Thermoelectric Effect Of Ba-Doped BiCuSeO Thin Films

The light-induced transverse thermoelectric?LITT?effect is a special photothermoelectric phenomenon,showing important application prospects in the field of new type uncooled wide-band photodetectors.The LITT effect originates from the anisotropy of Seebeck coefficient of the material,and it can be observed only in samples with an inclined crystal structure.The amplitude of LITT voltage is proportional to the temperature difference ?T_z between surface and bottom of the sample as well as the anisotropic Seebeck coefficient ?S.BiCuSeO is a novel layered chalcogenide thermoelectric material.In this paper,the Pulsed Laser Deposition?PLD?method was used to prepare the c-axis tilted BiCuSeO-based thin films on single crystal substrates.Some modified approaches,such as Barium doping,adding an additional light absorption layer on film surface,as well as metal nanoparticle compositing,were used.Our goal is to optimiae the photo-thermal-electric conversion efficiency and obtain higher voltage amplitude by adjusting the thermoelectric transport parameters or increasing the light absorption of the film.This will provide important guidance for designing high-sensitivity wide-band optical detectors based on LITT effect.The main research contents and conclusions are as follows:1.Bi_1-xBa_xCuSeO?x=0,0.03,0.06,0.09?thin films are prepared,and the influence of Barium concentration on LITT effect is studied.It is found that the LITT voltage sensitivity and response time are optimized in all doping films;as the Barium concentration x increases,the LITT voltage amplitude showes a tendency of firstly increasing and then decreasing,and the optimal voltage sensitivity reaches at 4.79V/mJ obtained in film of x=0.06.We believe that the optimization of sensitivity is resulted from the following two aspects:1)As increasing the Barium concentration x,the resistivity of the film decreases,which will lead to an increased light absorption coefficient as well as temperature difference ?T_z;2)The increased carrier concentration will resulte in an improvement in the anisotropy of Seebeck coefficient ?S of the film.For excessively doped film?x=0.09?,the crystal quality and tilted crystal orientation of the film are deteriorated,and the LITT characteristics become worse.2.The graphite and graphene light absorption layers are respectively coated on the surface of Bi_0.94Ba_0.06CuSeO film.We find that:1)The graphite light absorption layer can improve the photo-thermal conversion efficiency and avoid heating the film directly by the light source,which can enhance the LITT voltage amplitude for the irradiation of continuous lasers;however,for pulsed light sources,the heat flux density in the film is weakend due to the extended thermal relaxation time,leading to a decreased LITT voltage amplitude as well as an increased response time.2)Because of the lower light absorption rate,the graphene light absorption layer can not improve the LITT voltages for both pulsed and continuous light sources.3.The effect of metal nanoparticles on LITT effect is studied.1)When coating Ag nanoparticles on the surface of Bi_0.94Ba_0.06CuSeO film,an obvious"plasmon"peak at 450nm is observed.For both irradiations of 308nm pulsed laser and 450nm continuous light,the LITT voltage sensitivity are improved significantly;2)Bi_0.94Ba_0.06CuSeO/Au nanocomposite films are prepared.The Au nanoparticles in Bi_0.94Ba_0.06CuSeO film can effectively regulate the resistivity,thermal conductivity and the anisotropic Seebeck coefficient ?S of the film,thereby optimizing the output voltage sensitivity and responsiveness of the LITT effect.