In this thesis, the electronic and magnetic properties of Cr doped wurtzite ZnS were studied by means of most advanced theoretical approach density functional theory (DFT) using generalized gradient approximation (GGA) functional and its correction factor GGA+U. Calculations have shown that doping of chromium at cationic sites of wurtzite zinc sulphide results in formation of a p-type semiconductor. Addition of hubbard term in the system causes an increase in band gap value and creates a gap between spin up and spin down channels for 3d states of chromium atoms.
Chromium doped ZnS possess half metallic character because of excess in majority spin carriers than minority ones. Hopping of electrons in anti-bonding states of chromium atoms refers to the ferromagnetic behavior of the material. Half metallicity and ferromagnetic nature of the chromium doped wurtzite zinc sulphide makes this material a best candidate to be used in the field of spintronics.
For the past few decades, work in semiconductor field appears to be of substantial importance in industrial world and offers a new direction to upgrade the standards of life. This novel era of semi-conductors has remake the history of science with its groundbreaking technology and has proven to be an extensively emerging field to handle even single atoms and molecules for manipulation and fabrications. In the recent years, material science has open a new window towards applicability of semiconductor devices in electronics, spintronics and many other branches of science. Presently, II-VI materials have gain much value because of their broad range of applicability in advance fields of science. These elements involve transition metals like zinc, cadmium and nonmetals like oxygen, sulphur, selenium, tellurium. Due to their wide band gap, these compounds possess shorter wavelength and used in optoelectronic devices.
Table of Contents
1. INTRODUCTION
1.1 Research Problem
1.2 Research Plan
2. LITERATURE REVIEW
2.1 Literature Review
3. THEORETICAL BACKGROUND
3.1 Energy Band Theory
3.2 Semiconductors and their Characteristics
3.3 Direct/Indirect Band Gap Semiconductors
3.4 II-VI Compound Semiconductors
3.5 Zinc Sulphide
3.6 Exchange Interaction
3.6.1 Direct Exchange Interaction
3.6.2 Indirect Exchange Interaction
3.6.2.1 Double Exchange Interaction
3.7 Jahn Teller Effect
3.8 Techniques for Computational Study
3.9 Density Functional Theory
3.9.1 Many-Body Problems in Solids
3.9.2 Hohenburg-Kohen Theorems
3.9.2.1 First Hohenburg Kohen Theorem
3.9.2.2 Second Hohenburg Kohen Theorem
3.9.3 Kohan-Sham Equation
3.9.4 Exchange Correlational Functional
3.9.5 Local Density Approximation (LDA)
3.9.6 Local Spin Density Approximation (LSDA)
3.9.7 Generalized Gradient Approximation (GGA)
3.9.8 LDA and GGA with Hubbard Correction
3.9.9 Hybrid Functional
3.9.10 Tran-Blah Modified Becke Johnson Potential (TB-mBJ)
3.10 Basis Sets
3.10.1 Slater-Type Orbital (STO)
3.10.2 Gaussian-Type Orbital (GTO)
3.11 Amsterdam Density Functional (ADF)
4. COMPUTATIONAL TECHNIQUES
4.1 ADF-BAND
4.2 Brief Introduction to ADF-BAND
4.2.1 Features of ADF-BAND
4.2.2 Operating System for ADF-BAND
4.2.3 Electronic and Structural Parameters using ADF-BAND
4.2.4 Construction of wurtzite ZnS structure with ADF-BAND
4.2.5 Construction of a unit cell of ZnS
4.3 Computational Aspect
5. RESULTS AND DISCUSSIONS
5.1 Electronic Properties
5.1.1 Chromium Doped Zinc Sulphide: 16 atoms
5.1.2 Cr Doped ZnS: 32 atoms
5.1.3 Cr Doped ZnS: 64 atoms
5.2 Conclusion
Research Objectives and Topics
The research aims to investigate the electronic and magnetic properties of chromium-doped wurtzite zinc sulphide (ZnS) using density functional theory (DFT) methods, specifically focusing on the material's potential in spintronics applications.
- Application of generalized gradient approximation (GGA) and GGA+U functionals.
- Analysis of p-type semiconductor formation and half-metallic characteristics.
- Investigation of ferromagnetic behavior through electron hopping and exchange interactions.
- Evaluation of structural stability and band gap modification upon doping.
- Comparative study of chromium doping in different supercell sizes (16, 32, and 64 atoms).
Excerpt from the Book
3.6.1 Direct Exchange Interaction
When electrons of neighboring atoms interact with each other without any involvement of third party atom, then that type of interaction is direct. When electrons with same spin are kept at a distance then this reduces the coulomb repulsion, which is also the consequences of Pauli’s exclusion principle. When interaction is considered for transition metal doped semiconductors, then 3d or 4f orbitals exhibit high degree of localization and are very far away from the nucleus. Thus, for such type of materials direct interaction has negligible significance, and indirect interaction encounters in the system [37].
Summary of Chapters
CHAPTER 1: INTRODUCTION: Outlines the significance of semiconductor materials in modern electronics and introduces the specific focus on chromium-doped ZnS in the wurtzite phase for spintronic applications.
CHAPTER 2: LITERATURE REVIEW: Reviews previous experimental and computational studies on the electronic structure and band gap properties of zinc sulphide and doped systems.
CHAPTER 3: THEORETICAL BACKGROUND: Details the fundamental physics, including energy band theory, density functional theory (DFT), and the computational methods used to model these properties.
CHAPTER 4: COMPUTATIONAL TECHNIQUES: Describes the specific ADF-BAND software package, the construction of supercells, and the methodology employed for simulating chromium-doped ZnS.
CHAPTER 5: RESULTS AND DISCUSSIONS: Presents the findings regarding total and partial density of states (DOS) for various supercell sizes, discussing electronic behavior, band gaps, and magnetic properties.
Keywords
Zinc Sulphide, Chromium Doped, Density Functional Theory, DFT, GGA, Hubbard Correction, Spintronics, Ferromagnetism, Half Metallic, Band Gap, Wurtzite, Semiconductor, p-type, Exchange Interaction, ADF-BAND
Frequently Asked Questions
What is the primary focus of this research?
The research focuses on analyzing the electronic and magnetic properties of chromium-doped wurtzite zinc sulphide to evaluate its suitability for spintronic devices.
What are the central themes of this work?
The work explores semiconductor doping, computational physics (specifically DFT), magnetic exchange interactions, and the role of localized 3d states in determining material properties.
What is the main research objective?
The primary objective is to demonstrate that chromium-doped wurtzite ZnS exhibits half-metallic and ferromagnetic properties, identifying it as a promising candidate for spintronics.
Which scientific methods were utilized?
The study relies on density functional theory (DFT) using the ADF-BAND software, incorporating GGA and GGA+U functionals for optimized calculation results.
What topics are covered in the main body?
The main body covers the theoretical basis of band structures, the methodology for computational modeling of doped systems, and detailed discussions on the density of states for different atom concentrations.
Which keywords best describe this study?
Key terms include ZnS, chromium doping, DFT, spintronics, ferromagnetism, half-metallicity, GGA+U, and band gap engineering.
How does the Hubbard correction affect the results?
The Hubbard correction increases the calculated band gap and effectively separates the spin-up and spin-down channels for 3d states, providing a more accurate representation of the material's magnetic properties.
Why is the Jahn Teller Distortion significant in this study?
Jahn Teller Distortion is crucial as it removes state degeneracy, stabilizes orbitals, and plays a key role in splitting states, which directly influences the material's magnetic behavior.
- Citar trabajo
- SN Butt (Autor), 2017, Zinc Sulphide Doped With Chromium. A Density Functional Theory Study, Múnich, GRIN Verlag, https://www.grin.com/document/508622
