Quantum dots (QDs) are tiny semiconductor nanostructures that have garnered significant attention for future nanoscale applications in recent years. So far, there is still a challenge for the growth of QDs to control the composition, size, and morphology significantly. In our dissertation, we investigate the growth QDs using a plasma-assisted molecular beam epitaxy (PA-MBE) system with various characterization of QDs, mainly hexagonal boron nitride (h-BN) and indium gallium nitride (InGaN). In this dissertation, two research projects are discussed.
The first research project (Chapter 4) observes the growth of h-BN QDs on the surface of polycrystalline Ni film at 700 to 800 °C by PA-MBE. RHEED patterns can identify the surface condition during growth and BN formation. Observing the surface morphology of Ni films with FE-SEM and AFM revealed BN QDs on the Ni films. Raman spectroscopy and KPFM analysis confirmed the existence of h-BN QDs. Cathodoluminescence spectra showed h-BN QDs at wavelengths 546 and 610 nm. Impurities and vacancies in the trapping centres triggered this. Furthermore, the effect of substrate and boron source cell temperatures ware also discussed, suggesting that h-BN QDs grew better as the temperatures of boron K-cell and substrate growth increased.
The second research project (Chapter 5) is focused on the droplet epitaxy of InGaN QDs on Si (111) substrate. PA-MBE was used to examine the formation of In-Ga droplets in an ultra-high vacuum, followed by surface nitridation. During the droplet epitaxy technique, in-situ RHEED patterns confirm the transformation of amorphous In-Ga alloy droplets onto polycrystalline InGaN QDs, further verified by HR-TEM and XPS spectroscopy. The growth mechanism of InGaN QDs on silicon is investigated by varying the substrate temperature, In-Ga droplets' deposition time, and nitridation plasma duration, which are vital parameters. Self-assembled InGaN QDs can be achieved at 350 oC with 1.33 x 1011 cm-2 density and an average size of 13.3+3nm. Uncapped InGaN QDs emit visible red (715 nm) and infrared (795 and 857 nm) lights from the photoluminescence spectrum. The formation of Indium-rich composition of InGaN QDs by droplet epitaxy technique could be used to create optoelectronic devices with long wavelengths.

Chapter 1. Introduction ....... 2
1.1 Overview 2
1.2 Motivation and objectives 4
1.3 Organization of dissertation 5

Chapter 2. Literature Review .........10
2.1 Hexagonal Boron Nitride (h-BN) 10
2.2 Indium Galium Nitride (InGaN) 15
2.3 Substrates 20
2.3.1 Nickel (Ni) 20
2.3.2 Silicon (Si) 20
2.4 Self-assembled Quantum Dots (QDs) 21

Chapter 3. Research Method .......26
3.1 Plasma-assisted molecular beam epitaxy (PA-MBE) 26
3.2 Growth Mechanism of InGaN QDs by Droplet Epitaxy 32

Chapter 4. The Growth of Hexagonal Boron Nitride Quantum Dots on Polycrystalline Nickel Films by Plasma-Assisted Molecular Beam Epitaxy .....36
4.1 Materials and Methods 36
4.1.1 Preparation of Substrate 36
4.1.2 The Growth of h-BN QDs 36
4.1.3 The Growth Characterizations of h-BN Quantum Dots 37
4.2 Results and Discussion 38
4.2.1 Reflection High-Energy Electron Diffraction (RHEED) Pattern 38
4.2.2 Field Emission-Scanning Electron Microscopy (FE-SEM) 39
4.2.3 Atomic force microscopy (AFM) and Kevin probe force microscopy (KPFM) 40
4.2.4 Raman spectroscopy 42
4.2.5 Cathodoluminescence (CL) spectroscopy 43
4.3 Conclusions 44

Chapter 5. Droplet Epitaxy of InGaN Quantum Dots growth on Silicon (111) by Plasma-Assisted Molecular Beam Epitaxy .....48
5.1 Materials and Methods 48
5.1.1 Substrate preparation 48
5.1.2 InGaN QDs growth 48
5.1.3 Characterizations of InGaN quantum dots 49

5.2 Results and Discussion 50
5.2.1 Reflection high energy electron diffraction 50
5.2.2 Field emission scanning electron microscopy (FE-SEM) 51
5.2.3 Atomic force microscopy and scanning kevin probe force microscopy 54
5.2.4 X-ray photoelectron spectroscopy (XPS) 56
5.2.5 Transmission electron microscopy 59
5.2.6 Photoluminescence spectroscopy 60
5.3 Conclusions 62

Chapter 6. Overall Conclusions .....66
6.1 Overall Conclusions 66
6.2 Future recommendations. 67

References .......70

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