Research On The Structure And Thermoelectric Properties Of Semiconductor/Metal Periodic Nanostructured Multilayer Films Based On Silicon And Telluride Antimony

Thermoelectric material is a kind of materials,which convert the electrical energy to thermal by thermoelectric effect.As no moving parts,it will have a long life and stability in a certain temperature.Meanwhile,thermoelectric materials can be good for utilization of waste heat,which characteristic is low energy density and instability of heat source.The periodic multilayer structures composed of semiconductor and metal are considered as an effective way to improve the efficiency of thermoelectric conver-sion.In this paper,the high temperature thermoelectric material Si and the room tem-perature thermoelectric material Sb₂Te₃ are taken as the research object.Different types of semiconductor/metal?Au,Cu,Ag?periodic nanometer multilayer thin film structure have been designed.Meanwhile,the structure characteristics,heat transfer performance and electric transport mechanism have been systematically analyzed.Moreover,the thermal conduction mechanism of periodic nano-multilayer films with different Au lay-ers and the evolution of periodic nano-multilayer films under thermal annealing condi-tions were studied.The specific works are divided into the following five aspects:The Si/Si_0.75Ge_0.25/Au periodic nano-multilayer film structure with Au intercala-tion has been designed,meanwhile,the law of influence of heat conduction for the pe-riodic nano-multilayer film with the different number of Au intercalation and Si/Si_0.75Ge_0.25 component ratio has been studied.The results of heat conduction study show that:as the multilayer component is amorphous,the thermal conductivity is inde-pendent of the modulation period,which is decided by the component ratio of the mul-tilayer.Moreover,with the addition of the Au layer,the thermal conductivity is no change.The thermal conductivity?0.96 W/m?K?of the periodic nano-multilayer film?5 Au layers?is 37%of the theoretical value deduced by the classical formula,which indicates that the metal/semiconductor interfaces have a huge influence on the thermal conductivity of the multilayer film.Si/Au periodic nano-multilayer film structures have been constructed,and the heat conduction mechanism of ultra-thin periodic nano-multilayer film by adjusting the thickness of Au nano-layers has been explored.The results show that as the thickness of the Au layers are greater than 8 nm,electrons are the heat conduction medium in the metal layer of the periodic nano-multilayer film,and the coupling of phonons and elec-trons has a greater influence on the heat conduction;while the thickness of the Au layer is less than 8 nm,phonon conduction is the main way of thermal conduction in the metal layer and electron tunneling also has an effect on heat conduction.Moreover,When the thickness of the Au layer is 1 nm,the Si/Au periodic nano-multilayer film has ultra-low thermal conductivity and the value?0.6 W/m?K?is only 42%of the pure Si film.The results are helpful for understanding the heat transfer process of the semiconduc-tor/metal multilayers,providing guidance for the preparation of ultra-low thermal con-ductivity semiconductor/metal multilayer thin film thermoelectric materials.The effect of the thickness of Au layer on the thermal conductivity of Sb₂Te₃/Au periodic nano-multilayer films has been systematically studied.The results show that the thermal conductivity of the Sb₂Te₃/Au multilayer film decreasing previously and increasing later with the increase of the thickness of the Au layer.The reason for the law is that the thermal conduction is affected by the atomic diffusion region between the semiconductor/metal layers.When the thickness of the Au layer is 7 nm,the Sb₂Te₃/Au periodic nano-multilayer film has an ultra-low thermal conductivity,and the value?0.68 W/m?K?is only 69%of pure Sb₂Te₃ films.A novel"crystallization-roughening-fragmentation-dissolution"mechanism was proposed to understand the influence of annealing temperature on the structure of Sb₂Te₃/Au periodic nano-multilayer films.The results show that when the annealing temperature is lower than a certain temperature?423 K?,the structure and electrical properties of the periodic multilayer film can maintain stability;when the temperature is increased to 473 K,the layered structure of multilayer film disappears completely and the electrical performance of film with the thin Au layer has also changed dramat-ically.The results have important guiding significance for the practical application of Sb₂Te₃/Au periodic nano-multilayer film.The structure of Sb₂Te₃/Cu and Sb₂Te₃/Ag periodic nanofilms have been con-structed by molecular beam epitaxy.The influence mechanism of metal on the thermo-electric properties of the films has been analyzed.The results show that when the Cu layers are very thin,the Cu does not form layers,but exists as discontinuous nanopar-ticles,the Cu particles can effectively improve the electrical properties of the film be-cause of the carrier filtering effect;after annealing at 423 K,the power factor can reach480?W/?m?K²?.When the thickness of Ag is 4 nm,the power factor of Sb₂Te₃/Ag pe-riodic nano film is as high as 500?W/?m?K²?,which is 3.84 times that of Sb₂Te₃ film.This research provides a new idea for the preparation of high performance,low cost thermoelectric conversion materials.