鎢摻雜之碲化鍺第一原理研究

First-Principles Studies of W-Doped GeTe

張喬寓(Chiao-Yu Chang)

指導教授 ： 周美吟

國立臺灣大學/理學院/應用物理研究所/碩士(2021年)

https://doi.org/10.6342/NTU202104037

摘要

日常生活中，大量的能量以廢熱的形式不斷地被排放到大氣中，造成能源的浪費也嚴重影響地球環境，而熱電效應的應用是有望能解決廢熱問題的方式之一，且不會排放二氧化碳，能夠達成節能減碳的目的，其中鍺碲化合物（GeTe compound），經由多篇文獻證實具有良好的熱電優值（zT），其在立方相的高對稱性，以及菱形晶相中的能帶對齊（band convergence）及拉什巴效應（Rashba effect）等，使其成為非常有趣且有前景的材料。
本研究透過第一原理計算，以理論的方式，研究並探討鎢摻雜之碲化鍺。我們首先討論鎢摻雜的生成能，結果顯示其具有非常高的生成能，表示鎢較難在碲化鍺晶體中生成缺陷，但鍺空缺（Ge vacancies）的存在能夠大幅地降低鎢缺陷生成能，且鎢缺陷的存在亦能造成鍺空缺產生以及促進另一個鎢缺陷的生成。接著我們發現鎢的摻雜能夠與鍺及碲形成鍵結，並在原本碲化鍺的能隙中引入大量的能態，進一步的探討發現這些能態的電子密度分布集中在鎢原子附近，為相當局域化（localized）的能態。

關鍵字

第一原理 ； 熱電材料 ； 鎢摻雜 ； 鍺化碲 ； 能帶結構 ； 密度泛函理論

並列摘要

In our daily lives, tons of energy dissipates into the atmosphere in the form of waste heat, causing the waste of energy and damage to our living environment. The application of the thermoelectric effect is one of the promising ways to deal with this problem without emitting CO2, attaining energy-saving and carbon reduction. The GeTe compounds have been reported to have good figures of merits (zT). The high symmetry feature in the cubic phase, band convergence and the Rashba effect in the rhombohedral phase, etc., render GeTe-based materials interesting and promising materials.
In this work, W-doped GeTe is studied theoretically from first-principles calculation. Firstly, we discuss the formation energy of W doping, and the results show that the formation energies of W defects are quite high, indicating that it is hard to form W defects inside the GeTe crystal. However, the presence of Ge vacancies lowers the formation energy of the W dopant significantly. Furthermore, the presence of W defects can induce the formation of Ge vacancies and reduces the energy cost for the formation of another W defect. Then, we find that the W dopant would bond to Ge and Te atoms and induces localized states in the GeTe band gap.

並列關鍵字

first-principles ； thermoelectric material ； tungsten doping ； germanium telluride ； band structure ； density-functional theory

參考文獻

[1] J. P. Heremans, V. Jovovic, E. S. Toberer, A. Saramat, K. Kurosaki, A. Charoenphakdee, S. Yamanaka, and G. J. Snyder. Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states. Science, 321(5888):554-557, 2008.

[2] M. Hong, Z. G. Chen, L. Yang, Y. C. Zou, M. S. Dargusch, H. Wang, and J. Zou. Realizing zT of 2.3 in Ge1− x− ySbxInyTe via reducing the phase‐transition temperature and introducing resonant energy doping. Advanced materials, 30(11):1705942, 2018.

[3] L. Wu, X. Li, S. Wang, T. Zhang, J. Yang, W. Zhang, L. Chen, and J. Yang. Resonant level-induced high thermoelectric response in indium-doped GeTe. NPG Asia Materials, 9(1):e343-e343, 2017.

[4] G. J. Snyder and E. S. Toberer. Complex thermoelectric materials. Materials for sustainable energy: a collection of peer-reviewed research and review articles from Nature Publishing Group, 101-110, 2011.

[5] T. Siegrist, P. Jost, H. Volker, M. Woda, P. Merkelbach, C. Schlockermann, and M. Wuttig. Disorder-induced localization in crystalline phase-change materials. Nature materials, 10(3):202-208, 2011.