层状钴氧化物薄膜光诱导横向热电效应研究

发布时间：2018-03-11 21:48

本文选题：光诱导横向热电效应　切入点：c轴倾斜的Bi_2Sr_2Co_2Oy薄膜　出处：《河北工业大学》2016年博士论文　论文类型：学位论文

【摘要】：光诱导横向热电效应(简称LITT效应)是一种温差和电压方向相互垂直的热电效应,通常只能在c轴倾斜生长的薄膜、单晶及人工构建的多层结构中观测得到。该效应源于材料各向异性的Seebeck系数,实质是一个光-热-电转换过程。自LITT效应发现20多年以来,几乎所有相关报道都集中在样品的几何参数对该效应的影响上,而极少涉及材料电、热输运参量的调控和优化,这也在一定程度上制约了LITT效应的发展。本文采用化学溶液沉积技术在c轴倾斜的La Al O3(001)单晶基片上外延生长了Bi_2Sr_2Co_2O_y热电薄膜,从电、热参量调控机理及温度场理论出发,研究了掺杂、氧空位和光吸收层等对薄膜LITT效应的影响。其目标是通过结构或微结构调控来优化薄膜材料的电、热输运参量及薄膜对光辐射的吸收,提高LITT效应中的光-热和热-电转换效率,为研制新一代基于LITT效应设计的高灵敏宽波段光探测器提供指导。主要实验结论如下:1.研究了基本实验参量如薄膜厚度、倾斜角度、激光入射方向、波长、能量等对Bi_2Sr_2Co_2O_y薄膜LITT效应的影响。实验发现当用不同波长激光对薄膜表面进行加热时均可以观测到横向开路电压信号且信号幅值与以上参量密切相关。进一步用热源(如电烙铁)替代光源,仍可以观测到开路电信号且信号幅值随热源温度升高而增大。分析认为该电压信号源于薄膜各向异性的Seebeck系数,即横向热电效应。2.通过改变样品后退火温度及气体氛围来调控薄膜的微结构和氧含量,研究了薄膜微结构和氧含量对其LITT效应的影响。实验发现退火温度高、氧含量大的样品电阻率减小(薄膜电阻率减小可增大其上下表面温差)而热导率增大且Seebeck系数呈现更强的各向异性,因此LITT效应输出电压具有更大的灵敏度和更快的响应时间。在此基础上,进一步研究了掺杂和双层结构对薄膜LITT效应的影响。实验发现Bi_2Sr_2Co_2O_y掺入Pb和构建Bi_2Sr_2Co_2O_y/Pb_2Sr_2Co_2O_y多层膜均可以可以增大薄膜ab平面和c轴方向Seebeck系数的差值ΔS,导致LITT效应输出电压灵敏度提高。3.以石墨、碳纳米管、纳米银颗粒等材料为光吸收层,研究了光吸收层类型、几何尺寸(面积、厚度)对薄膜LITT效应的影响。结果表明:a)所有光吸收层均可增强LITT过程中的光-热转换效率,使薄膜上下表面温差增大,从而增大LITT效应输出电压的灵敏度。b)当光吸收层面积与入射光斑面积相等,厚度恰好实现完全光吸收时,LITT效应中光-热转换效率最高,获得的输出电压最大。c)三种光吸收材料中,碳纳米管光吸收层的效果最佳。4.研究了Bi_2Sr_2Co_2O_y薄膜的变温LITT效应。在30-150K和20-250℃的温度范围内,电压幅值随测试温度的升高而增大。我们认为:低温区(150-30K)电压幅值的减小与Bi_2Sr_2Co_2O_y薄膜ΔS的减小及因电阻率的增大导致的薄膜上下表面温差减小均有关系;但高温区(20-250℃)电压幅值增大的物理机制有待于进一步探究。除LITT效应外,我们还研究了非斜切Bi_2Sr_2Co_2O_y薄膜的横向光伏效应及Bi_2Sr_2Co_2O_y/Si异质结的变温整流及光伏特性。上述结果表明Bi_2Sr_2Co_2O_y薄膜不仅在热电器件而且在基于横向热电效应设计的光、热探测器等领域都具有潜在的应用前景。
[Abstract]:Light induced transverse thermoelectric effect (LITT effect) is a kind of thermoelectric effect of temperature and voltage direction perpendicular to each other, usually only inclined thin films grown on the c axis, the observed single crystal and multilayer structure is constructed. The Seebeck coefficient of the effect stems from the material anisotropy, is essentially a light heat electricity the conversion process. Since the discovery of LITT effect for 20 years, almost all relevant reports have focused on the geometric parameters of the samples affect the effect, and rarely involve material electricity, control and optimization of operation parameters of heat transmission, this has to a certain extent, restricts the development of the LITT effect in La Al. O3 tilt c axis adopts chemical solution deposition (001) single crystal substrate of Bi_2Sr_2Co_2O_y thermoelectric films, starting from the electric thermal parameters, regulation mechanism and temperature field theory, studied the doping, oxygen vacancy and light absorption layer of thin film LITT. Should the effect. Its goal is through the structure or micro structure control to optimize the thin film materials, heat transport parameters and film for light radiation absorption, improve the LITT effect in light - heat - electricity conversion efficiency, for the development of a new generation of Takama Mihiro band LITT effect based on the design of optical detectors provide guidance the main conclusions are as follows: 1.. Experimental study on basic experimental parameters such as film thickness, inclination angle, the direction of the incident laser energy, wavelength, influence on the LITT effect of Bi_2Sr_2Co_2O_y films. The experimental results showed that when using different wavelength of laser heating of the film surface can be observed when the lateral open circuit voltage signal and signal amplitude and the above parameters are closely related further. With the heat source (such as electric iron) to replace the light, still can be observed in open circuit of electric signals and signal amplitude increases with the increase of heat source temperature. Analysis shows that the voltage signal source in anisotropic thin film The Seebeck coefficient of the opposite sex, namely micro structure and oxygen content of the transverse thermoelectric effect by changing the.2. samples after annealing temperature and atmosphere control film, study the effect of film microstructure and oxygen content on the LITT effect. The experimental results showed that high annealing temperature, oxygen content of large sample resistivity (thin film resistivity reduction can be reduced increase the surface temperature difference) and anisotropic thermal conductivity increases and the Seebeck coefficient is stronger, so the LITT effect of the output voltage has greater sensitivity and faster response time. On this basis, further studied the effects of doping and double layer structure of thin film LITT effect. The experimental results showed that Bi_2Sr_2Co_2O_y doped Pb and Bi_2Sr_2Co_2O_y/Pb_2Sr_2Co_2O_y multilayer construction film can increase value delta film ab plane and C axis direction Seebeck coefficient of S, leading to LITT output voltage sensitivity of.3. to improve the effect of stone Graphite, carbon nanotube, nano silver particles and other materials for the light absorption layer of the light absorbing layer type, geometry size (area, thickness) of the film LITT effect. The results showed that: a) all the light absorption layer can be enhanced in the process of LITT light heat conversion efficiency, so that the surface temperature difference increase film the sensitivity of.B, thereby increasing the output voltage of the LITT effect) when the light absorption layer area and incident spot area of equal thickness just complete absorption, LITT effect of light heat conversion efficiency is the highest, the maximum output voltage obtained by the.C) three light absorbing materials, carbon nano tube temperature and LITT effect of light absorption layer the best.4. Bi_2Sr_2Co_2O_y films were studied. The temperature range of 30-150K and 20-250 DEG C, the voltage amplitude increases with the increase of temperature. We believe that: low temperature region (150-30K) and Bi_2Sr_2Co_2O_y S of the film decreases the amplitude of voltage reduction Small and lead to the increase of the resistivity of the film due to surface temperature difference decreased; but the high temperature (20-250 DEG C) physical mechanism of voltage amplitude increases need to be further studied. In addition to the LITT effect, we also study the non vicinal Bi_2Sr_2Co_2O_y film lateral photovoltaic effect and Bi_2Sr_2Co_2O_y/Si heterojunction rectification and photovoltaic properties. The temperature the results show that the Bi_2Sr_2Co_2O_y films not only in the thermoelectric device and thermoelectric effect in the horizontal design based on a light, has a potential application prospect in areas such as thermal detectors.

【学位授予单位】：河北工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O482.6;O484

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