Luận án tiến sĩ: Nghiên cứu tính chất nhiệt điện của màng ZnO掺杂Ga và In

VIETNAM NATIONAL UNIVERSITY - HO CHI MINH UNIVERSITY OF SCIENCE INSTITUTE FOR NANOTECHNOLOGY PHAM THANH TUAN ANH Doctoral Thesis Ho Chi Minh City — 2024 VIETNAM NATIONAL UNIVERSITY - HO CHI MINH UNIVERSITY OF SCIENCE INSTITUTE FOR NANOTECHNOLOGY PHAM THANH TUAN ANH STUDYING THERMOELECTRIC PROPERTIES OF Ga AND In CO-DOPED ZnO THIN FILMS Specialty: Materials Science Code: 62440122 Reviewer 1: Assoc. Nguyén Tran Ha Reviewer 2: Assoc. Nguyén Manh Tuan Reviewer 3: Assoc. Dao Vinh Ai Independent reviewer 2: Assoc.

Nguyễn Dang Nam SUPERVISORS 1. Tran Cao Vinh 2. Phan Bach Thang Ho Chi Minh City — 2024 Declaration I declare that my PhD thesis in Material Science, with the title “Studying thermoelectric properties of Ga and In co-doped ZnO thin films” is a scientific work done by myself under the supervision of Assoc. Tran Cao Vinh and Prof.

Phan Bach Thang. The research results of the thesis are completely honest and accurate, and do not coincide with previous studies that have been domestically and internationally published. Candidate Pham Thanh Tuan Anh Acknowledgments As I reach the culmination of my doctoral journey and prepare to submit this thesis, I am filled with immense gratitude and a profound sense of accomplishment. This academic endeavor would not have been possible without the unwavering support, guidance, and encouragement of numerous individuals who have played significant roles in shaping my academic and personal growth.

I would like to express my heartfelt appreciation to all of you. I am deeply grateful to Vietnam National University Ho Chi Minh City, specifically University of Science, Center for Innovative Materials and Architectures, and Institute of Nanotechnology, for providing me with the opportunity to work, study, and pursue my doctoral studies. The intellectual environment, state-of-the-art facilities, and exceptional faculty members have been instrumental in fostering my research skills and cultivating a passion for knowledge. I would like to express my sincere gratitude to my supervisors, Assoc.

Tran Cao Vinh and Prof. Phan Bach Thang. Their expertise, guidance, and patience have been invaluable throughout this research journey. Their unwavering support and constructive feedback have not only strengthened the quality of this thesis but have also helped me grow as a researcher.

I am truly fortunate to have had their instruction, and their influence will remain with me as I embark on future endeavors. I would like to express my appreciation to my colleagues at Laboratory of Advanced Materials, Faculty of Materials Science and Technology, Faculty of Physics and Engineering physics, and INOMAR Center, with whom I have had the privilege to collaborate and exchange ideas, especially MSc. Nguyen Huu Truong, MSc. Hoang Van Dung, Assoc.

Pham Kim Ngoc, Dr. Ta Thi Kieu Hanh, Dr. Le Tran, MSc. Lai Thi Hoa, Dr.

Tran Quang Minh Nhat, MSc. Truong Cao Dai, MSc. Nguyen Duy Khanh, MSc. Doan Thi Tu Uyen, and BSc.

Phan Thi Thuy Trang. Your assistance, insights, and discussions have broadened my perspectives, challenged my assumptions, and elevated the quality of my research. To my friends and students, thank you for standing by me through difficulties. Your support and encouragement have been a constant source of strength throughout my doctoral pursuit.

Your belief in my abilities has pushed me forward and made the process enjoyable. I cherish the memories we have created together and look forward to many more adventures in the future. My heartfelt thanks go to my loving family, my grandparents, my parents, my brothers, and my relatives for their unconditional love and constant encouragement. Your unwavering belief in my potential has been the driving force behind my achievements.

Your sacrifices and understanding have made it possible for me to focus on my studies and pursue my passion wholeheartedly. I am eternally grateful for the support you have provided. My deepest love goes to my beautiful wife, MSc. Le Truong Kieu Oanh and my children for your support, love, and care.

All of you are the biggest motivation for me to endeavor. I would also like to especially thank Prof. Kuei-Hsien Chen (Academia Sinica, Taiwan), Prof. Sungkyun Park (Pusan National University, Korea), Prof.

Su-Dong Park (Korea Electrotechnology Research Institute, Korea), Prof. Ohtaki Michitaka (Kyushu University, Japan), and everyone who have contributed to my academic and personal growth, through scientific instruments, experimental analyses, discussions, encouragement, or a simple act of kindness. Last but not least, I would like to acknowledge financial support from Vietnam Ministry of Science and Technology, National Foundation of Science and Technology Development of Vietnam (NAFOSTED), Vietnam National University Ho Chi Minh City (VNU-HCM), University of Science, Vingroup Innovation Foundation (VINIF), and Vallet Scholarship. Contents Thesis information .0009009 009 00966090 i List of figures and graphs.ccsccssssscscsscccsscessscssccccsscsscscssccsesscccssessscsssccsesecees iii List of data tables.

HH 0000404005000 00900 ix List of symbols and aCTOIIVITS. HC 001060060010 400050004084 00 xi Chapter 1. Overview and mOfÏVAfÏOII. Evaluation of thermoelectric DerfOTmaiCe.

Dimensionless figure of merit and power ÍaCfOT. Quality factor oo. Trade-offs among TE parameters. «kg HH ng ng 8 1.

Seebeck COeÍICITIL.- G9 HH HH ng nh 8 1. Density-of-state (DOS) effective mass. Optimization prObÏ€mm. Thermoelectric ZnO Imiaf€TIÌÏS.-- óc 11212119111 1 2 1 vn ng re 12 1.

Suitability for power-generation appÏ1CafIO'S. Research literature and Motivation .-- 5 55 + ke 14 IS Noi ỆPP£POIIIIOỔOỜOỔ3. Thin-film Immaf€T1AÌS. - 5 5 S131 vn ng rn 17 1.

Scientific ideas and DUTDOS€S .-- - - 131 v1 1 H1 ng ng ng 20 1. Dimension reduction apprOachh. Synthesis technique s€Ï€CfIOT. Experiments and metho(Ì0ÌOĐÏ€S.

--s- <5 e< se< se ess=seesesse25 2. Materials and composition calculation. Bulk material synthesis 718. Thin-film synntheSI1S.-- 5 11v SH HH HH 30 2.

Fabrication of sputtering farB€fS. Deposition DTOC€SS.- HH HH HH 32 2.-- -- << + E11 vn ng ng nệt 34 2. X-ray photoelectron SD€CfTOSCODY. Photoluminescence sD€CITOSCODV.

Seebeck and resistivity MeaSUFEMENL. Hall effect-based measurermehnf. Laser flash analysis. Ăn HT TH HH TH kg 41 2.

Time-domain thermoreflectance. Differential scanning Calorimetry .- 5 2 11311230 E911 9119 119 ng ng ng nệt 49 2. Other analysis technn1QU€S.- - -- <6 1x 19 E9 kg re 50 Chapter 3. Compensation of Zn substitution and secondary phase segregation in thermoelectric IGZO bulk materials.

Elemental binding energy analysis. Lattice defect eVaÏUALIOII. Electrical and thermopower Properties. Thermoelectric quality factor and figure Of T€TII.

Lattice-defect engineering in thermoelectric IGZO thin films. Dual-doping strategy 0. Composition and binding energy anaÌyS€S. Microcrystalline structure and morphoÌOØV.

Electrical and thermopower properties. Thermal properties and thermoelectric performance. --- ----- 96 ÝÄxU ni 8v an. Chemical binding state and structural anaÏysS1S.

Energy band structure and point def€CfS. - 2G G1 ng TH ni HH nà 114 Chapter 5. Fermi-level and band structure modification in thermoelectric properties of IGZO thin films. Crystallography, band structure, and Fermi-level position.

Morphology and mICTOSfTUCẦUTC. Power factor components and band fÏattening. Thermal components and thermoelectric performance. 2G 0 0110119011930 911991 TH ng ve 138 Conclusions and future WOFKS.

so 555 5 2< 56 9 99919 989898950800956096856 139 List of related UDÌÏÏCiAÏOTNS,.004004 000 161 Thesis information Thesis title: Studying thermoelectric properties of Ga and In co-doped ZnO thin films. Speciality: Material Science Code: 62440122 Name of PhD Student: Pham Thanh Tuan Anh Academic year: 2017 Supervisors: Assoc. Tran Cao Vinh Prof. Phan Bach Thang At: VNUHCM- University of Science 1.

SUMMARY: This thesis aims to introduce, investigate, and optimize thermoelectric In and Ga co-doped ZnO materials in both bulk and thin-film forms which can convert efficiently waste heat to electricity at medium- and high-temperature regions. In particular, the structural and thermoelectric properties of the ZnO-based thin films are modified by controlling carrier concentration, mobility, Fermi level, density-of- state effective mass, and lattice defects in the films. This research is an important step toward fabricating real TE modules, specifically thin-film devices. Furthermore, the effects of dopants on electrical and phonon transport mechanisms are clarified.

This understanding can orient for other dopants in thermoelectric ZnO-based materials. NOVELTY OF THESIS: i. The one-step prepared IGZO bulks which were directly sintered at 1400°C obtain the lowest thermal conductivity and the highest power factor, especially at high temperature. The spinel phase segregation is found to be the main reason.

The analysis of secondary phase-controlled TE performance in terms of DOS effective mass, weighted mobility, and quality factor can be viewed as a novel approach for ZnO-based system. It is an effort to inherit good properties of the bulks, combined with the advantages of thin films, to optimize the TE performance of the IGZO films. The TE properties of the IGZO films are controlled through lattice-defect engineering that was conducted in two ways: dual-doping and post-thermal treatment. The combination of the dual-doping effect and post-thermal treatment is found to reduce significantly the thermal conductivity of the IGZO thin films to 0.95 W/mK, leading to the highest figure of merit ZT = 0.

Band structure modification is found one of the state-of-the-art strategies to control electrical and thermal transport properties, and optimize the TE performance. Tuning In and Ga contents is found to coupling modification of Fermi level and band flattening, leading to the ZT of 0.2 and PF of 745.2 uW/mK? at 573 K for the IGZO films deposited from the Ino. It proposes that the IGZO thin films approach the high ZT region (ZT = 0.2) of advanced nanostructured ZnO- based bulks. The determination of thermal conductivity is normally challenging for thin- film materials due to their transparency, and ultra-fast thermal diffusivity, which cannot be measured by common laser flash analyses.

In this thesis, the thermal diffusivity and conductivity of the IGZO thin films were estimated using the time- domain thermoreflectance (TDTR) technique with high sensitivity and accuracy. APPLICATIONS/ APPLICABILITY/ PERSPECTIVE i. The introduction of novel IGZO thin films with optimized TE performance can continue to be published, and extend to other dopants in ZnO-based materials. |The IGZO bulks can be applied for thermoelectric power generation batteries.

The IGZO thin films can be used in miniaturized devices, such as power supply for the Internet of Things and for powering wearable electronics/sensors powered by body heat. -11- List of figures and graphs Figure 1. Thermoelectric effects: (a) Seebeck effect, (b) Peltier effect, and (c) Thomson effect, including absorption and evolution of heat. Dependence of Seebeck coefficient S, electrical conductivity ø, thermal conductivity x, power factor PF, and figure of merit ZT on carrier concentration n.

Structural model of hexagonal wurtzite of ZnO material. Some thermoelectric materials with appropriate operating temperature ranges. Adapted from the Refs. Description of top-down approach for synthesizing ZnO-based thin films.

A comprehensive characterization is essential for modifying the structure, properties, modeling, and processing of ZnO-based mat€r1aÌS. The preparation processes: (a) ball milling, (b) the 1“ step — sintering of one-step preparation, and precursor powder preparation of two-step preparation, (c) the 2TM step — sintering of two-step preparation; (d) naked-eye photograph and (e) volumetric change of the IGZO bulks sintered by various prOCesSes. Temperature setpoints and hourly schedule for the thermal processes of DI e0) Tố ằẻ ằe. Homemade 3-inch targets with various compositions after many times of sputtering: (a)-(b) Representative green compact body prior to sintering, (c) ZnO, (d) GZO, (e) IGZO 0.

Sputtering system Leybold Univex-450 at AM-Lab. Measurement configurations of (a) Seebeck coefficient, (b) resistivity, and (c) thin-film modes; (d) commercial ULVAC ZEM-3 system at KERI; (e) commercial Linseis LSR-3 system at INOMAR Center. Commercial Hall measurement systems: (a) Room-temperature Ecopia HMS-3000, (b) the HTSST3 heated stage sample kit to 300°C at IAMS, and (c) design of Ecopia HMS-5500 and experiments on it at KERI. (a) Overview of a typical LFA system, (b) principle of LFA technique, and (c) typical transient temperature rise curve from LFA.

Commercial LFA systems: (a)-(b) Netzsch LFA-457 system, and coating samples with graphite prior to the measurements at KERI; (c) Linseis LFA500/1000 system at INOMAR Center; and (d) KEM LFA-502 at Kyushu University.