VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY LA THI NGOC MAI SOLUTION-PROCESSED SEMICONDUCTING AND MAGNETIC Ni-DOPED CuO THIN FILMS: PREPARATION AND CHARACTERIZATION MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY LA THI NGOC MAI SOLUTION-PROCESSED SEMICONDUCTING AND MAGNETIC Ni-DOPED CuO THIN FILMS: PREPARATION AND CHARACTERIZATION MAJOR: NANOTECHNOLOGY CODE: 8440140.11 QTD RESEARCH SUPERVISORS: Assoc. BUI NGUYEN QUOC TRINH Prof. NGUYEN HOANG LUONG Hanoi, 2021 Acknowledgement First of all, I would like to sincerely thanks my two supervisors Assoc. Bui Nguyen Quoc Trinh and Prof.
Nguyen Hoang Luong for their unending support, encouragement, and inspiration throughout my master course. Under their guidance, I have had extensive knowledge and insight into materials science and nanotechnology, including modern thin-film development, which helped me to gain a wholesome idea of the field. I would always cherish the time I spent under their tutelage. I would like to especially thank Assoc.
Dang Van Thanh, who guided me when I carried out experiments during my internship. I learned a lot from him in the field of electrochemistry. His support and insightful comments aided me in completing this research. Besides, I would like to thank Dr.
Nguyen Quang Hoa, University of Science, Vietnam National University, Hanoi, for allowing me to perform data analysis and measurements in this study. Moreover, I would like to give thanks to all the lecturers and researchers in Nanotechnology Program, Vietnam Japan University, who have imparted useful knowledge and supported me to accomplish this thesis. I would express my thanks to Vietnam Japan University for providing me with the facilities I am required to implement my project. Last but not least, I especially wish to thank family members and friends who always encourage and support me through the past 2-year master's course, to overcome any difficulty.
This work is fully supported by the project with the code number of VJU.03, from Vietnam Japan University, under Research Grant Program of Japan International Cooperation Agency. Hanoi, 2021 Master’s student La Thi Ngoc Mai TABLE OF CONTENTS LIST OF TABLES .i LIST OF FIGURES. ii LIST OF ABBREVIATIONS. Dilute Magnetic Semiconductors (DMS).
Thin film semiconductors. Cupric oxide thin films. Overview of deposition techniques. Physical deposition techniques.
Chemistry deposition techniques. Spin-coating techniques. Motivation and the objectives of the studies .18 CHAPTER 2: FILM DEPOSITION AND CHARACTERIZATION. Synthesis of precursors.
Thin film deposition. Deposition of Ni-doped CuO thin films. Scanning electron microscopy (SEM). UV-Vis spectroscopy.
Four-probe measurement system. Electrochemical Impedance Spectroscopy (EIS). Vibrating Sample Magnetometer (VSM) .30 CHAPTER 3: RESULTS AND DISCUSSION. Reaction mechanism of precursor solution.
Analysis of Ni-doped CuO thin films on glass substrates. Crystal-structure properties. Surface-morphology properties. Analysis of Ni-doped CuO thin films on the ITO substrates.
Crystal-structure properties. Surface-morphology properties .52 LIST OF TABLES Table 1. High-temperature oxide-based DMS (adapted from ref. Crystallographic parameters (from ref.
Thin film deposition methods (adapted from ref [47]). List of chemical compounds. Mass of chemicals used to manufacture precursors with difference Ni doping concentrations. Example of Nyquist graph and the usual equivalent circuit of a metal oxide electrode [66].
Measured electrical characteristics of Ni-doped CuO thin films with 0, 0.% of Ni doping on the glass substrates.41 i LIST OF FIGURES Figure 1. Schematic showing a magnetic semiconductor (A), a non-magnetic semiconductor (B), and a diluted magnetic semiconductor (C) [4]. Schematic diagram of sputtering [47]. Sol-gel process [54].
Schematic of a chemical bath deposition [56]. The SILAR deposition process [58]. The stages of thin film formation using spin-coating process [60]. Precursor solution preparation process.
Spin-coating system (a), annealing furnace (b). Electromagnetic radiation spectrum. Diffraction of X-rays by a crystal. Schematic diagram of a Scanning Electron Microscope [62] (a), SEM machine in this study (b).
Schematic of four-point probe configuration. Model of an electrochemical electrode system and its equivalent electrical circuit [65]. The change of concentration, solvent, additive, and Ni2+: MEA ratio to the solubility of nickel salt. CuO precursor solution (a), and Ni-doped CuO precursor solution in the range 0 – 4 wt.
Schematic drawing of the chemical equilibria involved in the Ni and Cu ions sol-gel process. XRD patterns of the un-doped and Ni-doped CuO thin films on glass substrates. The XRD patterns in the range 30° - 40° of the films on the glass substrates. Surface SEM images of Ni-doped CuO thin films with various Ni ratios on glass substrates.
The optical absorbance graph of Ni-doped CuO films on glass substrates. The optical bandgap versus Ni doping concentrations of Ni-doped CuO films on glass substrates. M-H curves of the Ni-doped CuO thin films on glass substrates. M-H curves for NiO powder and Ni-CuO film.
XRD patterns (a), the enlarged diffraction pattern in the range 35° to 40° (b) of all films on the ITO substrates. SEM images of CuO thin film and Ni-doped CuO thin films with 1, 2, 3, 4 wt.% deposited on the ITO substrates. Optical absorbance spectra of all films on the ITO substrates. Variation of bandgap energy for un-doped and Ni-doped CuO thin films on the ITO substrates.
Nyquist plot (a), the equivalent circuit model (b) of the Ni-doped CuO thin films on the ITO substrates. Variation in the resistive part with frequency of the undoped and Ni- doped CuO thin films on the ITO substrates.49 iii LIST OF ABBREVIATIONS CBD : Chemical bath deposition CVD : Chemical vapor deposition DMS : Dilute magnetic semiconductor FE-SEM : Field emission scanning electron spectroscopy MEA : Monoethanolamine RTFM : Room temperature ferromagnetism SEM : Scanning electron spectroscopy SILAR : Successive ionic layer adsorption and reaction SQUID : Superconducting quantum interference device UV-VIS : Ultravilolet-Visible VSM : Vibrating sample magnetometer XRD : X-ray diffraction iv INTRODUCTION Conventionally, electronic devices use an electron state, which is an electrical charge for information processing. One method for increasing information storage capacity and signal processing speed in electronic devices is to reduce the size of electronic components such as transistors or capacitors. Both coding and decoding processes will face extreme difficulty as the size of the transistor cell continues to be shrunk due to the quantum effect.
The spintronic device is a candidate technology for addressing the major issues found in conventional electronic devices. The spintronic device combines charge-based semiconductor property with magnetic property based on spin effect to carry and store information in a single device. Dilute Magnetic Semiconductor (DMS) is one of the most interesting materials for the development of spintronic devices containing the functional features mentioned above. The advantages of spin-based DMS application are to improve integration density and higher data processing speed, higher efficiency, low power consumption, and better stability.
Therefore, researchers are always seeking DMS materials with magnetic behavior at room temperature, so that they can be manufactured in the electronics field. The p-type semiconductor cupric oxide (CuO) has antiferromagnetic characteristics. In addition, CuO has a good light absorption coefficient with low thermal emittance. The characteristic properties of CuO thin films such as photoelectric properties, crystal structure can be controlled by doping, annealing temperature, crystallization atmosphere, and so on.
So far, several studies have focused on the magnetic behaviors of CuO in combination with different magnetic ions. However, there are still a lot of remaining rooms to search for novel materials for the electronic device application. In this thesis, CuO thin films doped with transition metal ions Ni were fabricated by the solution-processed method. Using the spin-coating process, thin films with various Ni doping ratios were coated on glass and ITO substrates.
The structural, morphological, optoelectrical and magnetic characteristics of the thin films are all studied. The achievement results pointed out that the Ni-doped CuO films obtained can be considered 1 for a channel of thin film transistors or the applications in spintronic devices and noise suppressors. Dilute Magnetic Semiconductors (DMS) Spintronics, also known as spin electronics, is one of the next-generation fields in electronics that studies the spin and charge states of an electron [1]. By combining the spin of electrons with their charge, spintronic systems are most commonly realized in applications of existing electronic devices.
Spin-electronics consume less power and have larger memory and computing power in a smaller size than conventional electronic devices. Conventional magnetic storage devices used passive magnetoresistive sensors and memory elements comprised of ferromagnetic 3d metal alloy electrodes. The discovery of enormous magnetoresistance, in (Fe/Cr)n multilayers, and tunneling magnetoresistance later aided their growth [2]. In fact, magnetic semiconductors are difficult to develop in practical applications, as they exhibit ferromagnetic properties at low Curie temperatures, frequently below 100 K [3].
Thus, scientists have searched for and developed a new magnetic semiconductor material called diluted magnetic semiconductors (DMS) by adding a few percent of magnetic atoms to the structure of the non-magnetic semiconductor material. DMS, also known as semimagnetic semiconductors, are materials in which a few percent of magnetic elements substitute some of the cations in a host semiconductor. Semi-magnetic semiconductors have characteristics that differ from classical magnetic semiconductors, are distinguished by a regulated dilution of the magnetic part (Figure 1. In the DMS, the charge carriers of the electron state strongly interact with the local magnetic moments, resulting in the material's unique physical features.
Magnetic ions can affect the state of the semiconductor band when the DMS material is applied by an external magnetic field. The arrangement of the spins of the magnetic ions is affected by the applied magnetic field, which has an effect on the spins of the band electrons. Magnetic enhancement of magnetic ions onto semiconductors in this way, leading to giant magneto-optical effects, makes DMS materials even more interesting. Schematic showing a magnetic semiconductor (A), a non-magnetic semiconductor (B), and a diluted magnetic semiconductor (C) [4].
Metal transition doped compound semiconductors based on II-VI semiconductors are used to make DMS such as InMnAs [5] and GaMnAs [6]. Hole formation occurs when divalent metal ions replace trivalent metal ions in III-V semiconductor semiconductors, resulting in ferromagnetic order intermediates. GaMnAs have been chosen as a material in many spin-based device applications, including spin-polarized light emitters [7], and spin field-effect transistors [8] which exhibit a magnetic behavior at below room temperature (TC = 173 K) [9]. Therefore, these semiconductor compounds can only function at cold temperatures (T ~ 100 K), making II-VI DMS unsuitable for practical electronic applications.
For the applications of DMS materials in electronics devices, achieving room- temperature ferromagnetism (RTFM) has become a critical problem. Several experimental results over RTFM have been reported in recent years in several classes of DMS, including wide bandgap III-V semiconductors (GaN, GaP) and group IV semiconductors (Ge, Si) [10]. Ferromagnetism has been shown to be carrier-mediated, allowing magnetic behavior to be modified through charge manipulation. This has elevated oxide-based DMS to the status of critical material in the creation of electrical devices.
Furthermore, the majority of oxide-based DMSs are a type of large bandgap semiconductors (> 3 eV), which can provide an optoelectronic dimension to the next generation of spintronic devices. Several recent studies have investigated DMS oxide exhibiting ferromagnetic properties at room temperature. The ferromagnetic characteristics of Co-doped TiO2 material revealed for the first time by Matsumoto et al. 4 [11, 12], have gotten a lot of attention.1 summarizes the magnetic moments and TC values published in the literature for these DMS-based thin films.
Following that, numerous scientists discovered the ferromagnetic properties of ZnO doped with transition metals at ambient temperature [13, 14]. High-temperature oxide-based DMS (adapted from ref. Material Doping Moment TC (K) Ref (μB/3d ion) TiO2 1-2% Co 0.3 > 300 [26] More researches have recently been conducted on other promising metal oxides due to their intriguing properties. Copper (II) oxide (CuO) is a semiconductor material with interesting properties suitable for DMS fabrication research.
CuO is a high critical temperature superconductor because superconductivity in these systems is associated with Cu-O bondings [27, 28]. As a result, studying the magnetic characteristics of nano- sized CuO materials is extremely important.