Institut Penyelidikan dan Teknologi Nano Optoelektronik (INOR) - Tesis
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- PublicationModelling Of Inhomogeneous Vertical Underwater Optical Wireless Communication Links(2023-03)Sabril, Muhammad SafiyUnderwater optical wireless communication (UOWC) is becoming increasingly widespread, moving beyond its former restriction to military and defense applications to now also being used in commercial fields. Despite its growing popularity, designing UOWC systems is challenging due to the complex interaction of light with water. To overcome these challenges, this thesis proposes using inhomogeneous medium in UOWC channel modeling, as opposed to the traditional homogeneous medium model which assumes a single constant value for the ocean’s physical and chemical properties. The thesis presents two inhomogeneous models: Model II, based on the variation in chlorophyll concentration, and Model III, which includes the variation in both chlorophyll concentration and refractive index. These models are compared to Model I, the homogeneous model. To estimate the received power, channel bandwidth, and delay spread, the Monte Carlo (MC) technique was improved to account for medium inhomogeneity.
- PublicationEpitaxial Growth Of Iii-V Nitrides Based Light Emitting Diodes By Metal Organic Chemical Vapor Deposition(2023-03)Samsudin, Muhammad Esmed AlifThis research aims to improve the performance of indium gallium nitride (InGaN) based LEDs and to demonstrate a working aluminum gallium nitride (AlGaN) based LEDs through metal organic chemical vapour deposition epitaxy. The effect of gallium nitride (GaN) nucleation growth temperature, superlattice period, and indium composition on InGaN based LED performance was studied. It was found that growing GaN nucleation at 570°C reduced threading dislocations (TDs) in the overgrown GaN layer (which served as the LED base layer). At 570°C nucleation, larger 3D growths (islands) formed, promoting dislocation inclination, and thus reducing TDs. Subsequently, 20 periods of In0.04Ga0.96N/GaN SLs led to reasonable V-pits size. This increased holes injection into the multiquantum well and hence, improved the LED performance. This research also attempted to find out factors which limit the use of GaN substrates in InGaN based LEDs development over sapphire substrates, particularly pattern sapphire substrate (PSS), which is widely used in many studies, including in this research.
- PublicationSynthesis And Characterization Of Organic-inorganic Bismuth Halide Perovskites For Photonics Applications(2023-09)Heng, Han YannThe study focused on synthesizing organic-inorganic Bi-halides perovskite compounds using different halides (iodide, bromide, and chloride) in a low-toxic and eco-friendly manner. The aim was to develop Pb-free perovskite materials that are less hazardous for workers in the photonics industry and that can be produced using inexpensive and less complicated processes. In this regards, a hydrophobic phenylammonium cation ([(C6H5)NH3]+) was selected, which is known to contributed to a better sample stability. The synthesis methods involved three different approaches: one step solvent (OSS), OSS added oleic acid (OA), and a non-coordinated solvent method at different temperatures. The stability of the samples were evaluated, and it was observed that the ones synthesized at 60 °C exhibited the best stability for most of the solvents and types of halides. The strong ionic interaction between the BiX63- anion and the short short PhA+ cations in the 0D structure greatly contributed to its stability. In general, the PhA4BiCl6 sample showed the highest stability among the halides due to the stronger attraction between nucleus and electron. The study also involved the growth of a single crystal of PhA4BiI6 using a solvent evaporation technique from which the structure of the zero-dimensional (0D) perovskite compounds was determined, supported by field emission scanning electron microscopy with energy-dispersive X-ray (FESEM-EDX) and Fourier transform infrared (FTIR) spectroscopy results
- PublicationSpin Coated Gallium Oxide Thin Films And The Effect Of Mo-Doping Concentration On Luminescence Properties(2023-07)Wang TiankunBeta-type gallium oxide (β-Ga2O3) with ultra-wide band gap energy and good emission property is suitable for optoelectronic applications such as luminescence devices. However, the growth of good quality β-Ga2O3 films using low cost and simple techniques, particularly the sol-gel spin coating technique, is still remains challenging. For luminescence features, undoped and doped β-Ga2O3 emit multicolour emissions due to the multi-energy level of intrinsic vacancies, which is unsuitable for the display application. From the fundamental and engineering point of view, it is worth investigating the above topics. In this project, the β-Ga2O3 thin films synthesized by the sol-gel spin coating method and their photoluminescence were investigated. For the fabrication, the sol-gel spin coating growth conditions, and processes of the β-Ga2O3 thin films on Si and Al2O3 substrates were investigated. Special treatments on the substrate and the coated layer were conducted to improve the uniformity and smoothness of each coated layer and the final deposited film. Different spin coating cycles, and annealing temperatures were also investigated from the morphologic and optical aspects. Finally, a set of samples with 6-layers spin-coated films and annealed under different temperatures, i.e., from 900 °C, to 1100 °C were prepared. These samples were then subjected to an in-depth X-ray diffraction analysis. The results show that the micro strain is not the key factor for the Bragg peaks broadening. To investigate luminescence properties, a series of Mo-doped β-Ga2O3 on Al2O3 were synthesized. A green luminescence band associated with the Mo ion dxz-dyz band transition appeared slowly with the increase of the Mo-doping concentration.
- PublicationEpitaxial Growth Of Gan On Gan Multi Quantum Well For The Deep Green Light Emitting Diode(2022-10)Abdul Rais, Shamsul AmirThis work has focused on the effort of fabricating the deep green light emitting diode (LED). First, the multi-quantum well (MQW) that was expected to be able to emit a deep green wavelength was designed and fabricated. The MQW was first grown on a patterned sapphire substrate due to nucleation layer and lattice match which are nearest to the gallium nitride (GaN) substrate. The growth of six pairs of GaN/ InxGa1−xN layer that has 12.16/3.35 nm thickness was successfully carried out. The MQW has low crystal defect even when the indium ratio for InxGa1−xN layer growth was 9 times more than gallium. Previous research shows that a high indium ratio in GaN crystal growth would yield high strain but none of these have been observed. The MQW was later inserted into the full LED structure. The LED was grown on the GaN substrate. The resulting LED has good crystal quality, with dislocation of 8.7x107cm-2 . The photoluminescence (PL) spectrum also gives a good result, 568 nm which is in the deep green region. However, the device needed to be annealed to activate the p-type, and the wavelength blue-shifted greatly, 45nm after the annealing process. This prompted the introduction of the indium pre-flow technique to the later growth of the LED samples.