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

该项目的目标是在低温（<350 °C）和中温（400 - 700 °C）范围内外延MOCVD沉积热电材料薄膜，并确定其传输特性。量身定制的第15族和第16族金属有机前体，例如低价化合物E2 R4和E '2 R'2（E = Sb、Bi; E' = S、Se、Te）以及单源前体R2 EE' R '、（R2 E）2 E'、RE（E 'R'）2 und E（E 'R'）3（E = Sb、Bi; E' = S、Se、Te），它们在相当温和的温度下干净地分解，将被研究。二进制（Sb 2Se 3、Sb 2 Te 3、Bi 2Se 3、Bi 2 Te 3）及三元材料薄膜（SbxBi1-x）2Te3，Sb2（SexTe 3-x）、Bi 2（SexTe 3-x）以及复杂的多层结构将在系统的MOCVD研究中外延沉积，并且将发展不同化学成分对热电性能（例如电导率和热导率以及塞贝克系数）的影响的基本理解。材料薄膜的表征是必不可少的，以了解的前体，沉积温度，和基板材料的热电性能的具体影响所产生的材料薄膜。因此，薄膜将在Schulz小组中进行预表征（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-埃森大学纳米尺度分析跨学科中心; SAM，XPS，TOF-SIMS）以及我们的合作者Gabi Schierning博士（Seebeck系数，功率因数）和阿克塞尔Lorke教授（电导率）详细研究了有前景的薄膜。二元和三元材料薄膜的热导率的测定是本项目的关键，将由C。Jooss使用3-omega方法。仔细调查的温度依赖性的热导率，这将是在30 K至900 K的温度范围内进行的，给出了有价值的信息声子散射的影响点无序，晶界（低温）以及声子-声子散射（高温）。此外，将使用高分辨率和分析型TEM研究所选样品的缺陷和微观结构。非化学计量在晶界以及点缺陷和缺陷簇的合成参数和掺杂水平的函数是特别感兴趣的，将使用电子能量损失谱（EELS）和环形暗场（ADF）技术进行研究。原位TEM实验将提供有关热应力下行为的信息。超晶格对所选材料系统的热电性能的进一步优化的潜力将被研究。对于选定的样品，将分离出热导率的平面内和交叉平面系数。

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.