Epitaxial MOCVD deposition of thermoelectric material films and determination of thermoelectric properties including thermal conductivity

该项目的目标是在低(&lt；350°C)和中(400-700°C)温度范围内外延MOCVD沉积技术应用的热电材料薄膜，并测定其传输特性。将研究定制的15和16族金属有机前驱体，如低价化合物E2R4和E‘2R’2(E=Sb，Bi；E‘=S，Se，Te)和在较温和的温度下干净分解的单源前体R2Ee’r‘，(R2E)2E’，RE(E‘r’)2和E(E‘r’)3(E=Sb，Bi；E‘=S，Se，Te)。在系统的MOCVD研究中，将外延沉积二元(Sb2Se3，Sb2Te3，Bi2Se3，Bi2Te3)和三元材料(SbxBi1-x)2Te3，Sb2(SexTe3-x)，Bi2(SexTe3-x)以及复杂的多层结构，并对不同的化学组成对热电性能的影响，如电导率和热导率和塞贝克系数，有一个基本的了解。为了了解前驱体、沉积温度和衬底材料对所得到的材料膜的热电性能的具体影响，材料膜的表征是必不可少的。因此，薄膜将在舒尔茨基团中进行预表征(结晶度、表面形态、化学成分)。然后，在DFG研究基础设施中心ICAN(杜伊斯堡-埃森大学纳米尺度跨学科分析中心；SAM，XPS，TOF-SIMS)以及我们的合作者Gabi Schierning博士(Seebeck系数，功率因数)和Axel Lorke教授(电导率)，对有希望的薄膜进行详细研究。对当前项目至关重要的二元和三元材料薄膜热导率的测定将由C.Jooss教授使用3-omega方法完成。在30K到900K的温度范围内，对热导率的温度依赖性进行了仔细的研究，提供了关于点无序声子散射、晶界(低温)以及声子-声子散射(高温)影响的有价值的信息。此外，还将使用高分辨率和分析性的透射电子显微镜对所选样品的缺陷和微观结构进行研究。晶界的非化学计量以及点缺陷和缺陷团簇作为合成参数和掺杂水平的函数引起了特别的兴趣，并将使用电子能量损失谱(EELS)和环状暗场(ADF)技术进行研究。原位透射电子显微镜实验将提供有关热应力下的行为的信息。超晶格在进一步优化所选材料体系的热电性能方面的潜力将被研究。对于选定的样品，将分离出平面内和平面内的导热系数。

The goal of this project is the epitaxial MOCVD deposition of thin films of thermoelectric materials for technical application in the low (<350 °C) and medium (400 - 700 °C)) temperature range and the determination of their transport properties. Tailor-made metal organic group 15 and 16 precursors such as low-valent compounds E2R4 and E'2R'2 (E = Sb, Bi; E' = S, Se, Te) and single-source precursors R2EE'R', (R2E)2E', RE(E'R')2 und E(E'R')3 (E = Sb, Bi; E' = S, Se, Te), which cleanly decomposed at rather mild temperatures, will be investigated. Binary (Sb2Se3, Sb2Te3, Bi2Se3, Bi2Te3) and ternary material films (SbxBi1-x)2Te3, Sb2(SexTe3-x), Bi2(SexTe3-x) as well as complex multilayer structures will be epitaxially deposited in systematical MOCVD studies and a fundamental understanding of the influence of different chemical compositions on the thermoelectric properties, e.g. electrical and thermal conductivity and Seebeck coefficient will be developed. The characterization of the material films is essential in order to understand the specific influence of the precursor, deposition temperature, and substrate material on the thermoelectric properties of the resulting material films. The films will therefore be pre-characterized in the Schulz group (crystallinity, surface morphology, chemical composition). Promising films are then investigated in detail in the DFG- research infrastructure center ICAN (Interdisciplinary Center for Analytics on the Nanoscale, University of Duisburg-Essen; SAM, XPS, TOF-SIMS) and by our collaborators Dr. Gabi Schierning (Seebeck coefficient, power factor) and Prof. Axel Lorke (electrical conductivity). The determination of the thermal conductivity of the binary and ternary material films, which is crucial for the current project, will be done by Prof. C. Jooss using the 3-omega method. Careful investigation of the temperature-dependence of the thermal conductivity, which will be done in the temperature range from 30 K to 900 K, gives valuable information on the influence of phonon scattering at point disorder, grain boundaries (low temperatures) as well as phonon-phonon scattering (high temperatures). In addition, the defect and microstructure of selected samples will be investigated using high-resolution and analytical TEM. Non-stoichiometries at grain boundaries as well as point defects and defect clusters as function of synthesis parameters and doping levels are of particular interest and will be investigated using electron energy loss spectroscopy (EELS) and Annular Dark Field (ADF) techniques. In-situ TEM experiments will give information on behavior under thermal stress. The potential of superlattices on the further optimization of the thermoelectric properties of selected material systems will be studied. The in plane and cross plane coefficients of the thermal conductivity will be separated out for selected samples.