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Abstract
This dissertation investigates advanced structural engineering techniques on different substrates to address the issue of large strain in InGaN-based light emitters, particularly at longer wavelengths. Initially, strain engineering on sapphire substrate involved growing a thick GaN underlayer; however, the strain relaxation achieved by this approach introduced numerous defects that negatively impacted device lifetime and efficiency. Further investigations of the typically used sapphire substrate were conducted using graded InGaN layers and semibulk structures; however, these strain engineering approaches showed very limited strain mitigation.
Given the limitations of sapphire substrates, the research shifted to an alternative approach using lattice-matching substrates: ZnO and ScAlMgO₄ (SAM) to reduce strain and accordingly enhance optical confinement factor. ZnO however, showed severe thermal instability; thus, it was excluded from further investigation. The preliminary results for InGaN/SAM showed significant improvements in the crystalline quality of InGaN, particularly for lattice-matching compositions intended for red light emitters. N-polar InGaN growth on SAM substrates with varying misorientations revealed a trade-off between surface morphology and crystalline quality, with the best results obtained using a 0.5° offset, achieving unprecedented crystalline quality.
Further analysis focused on the growth of GaN on m-plane SAM substrate, which was oriented along (10-13)-plane. This study highlighted the challenges in achieving a smooth surface and uniform crystalline quality across different azimuth angles, reflecting the structural anisotropy of growth along the m-plane SAM substrate.
Finally, this research has led to the first demonstration of a fully InGaN-based red light-emitting diode (LED) grown on a c-plane SAM substrate. This LED achieved a peak wavelength of 617 nm with promising light output and external quantum efficiency, marking a significant step toward developing longer-wavelength light emitters. These findings contribute to the advancement of full-spectrum RGB displays and high-performance optoelectronic devices, while also opening new horizons for biomedical applications.
Brief Biography
Mohammed Najmi is a Ph.D. candidate in Electrical Engineering at King Abdullah University of Science and Technology, focusing on Electro-Physics in the Energy Conversion Devices and Materials Laboratory (ECO Devices Lab). He holds an M.Eng. in Electrical Engineering from Texas A&M University, specializing in Devices and Nanotechnology, and has completed a Business Management course at Mays Business School. Additionally, he earned a B.Sc. in Applied Electrical Engineering from King Fahd University of Petroleum and Minerals (KFUPM). Mohammed brings over nine years of experience in advanced nanofabrication and characterization technologies, having worked at Texas A&M Aggiefab, KAUST Nanofabrication & Imaging, and Characterizations Corelabs. Throughout his education journey, he has developed expertise in material growth, device characterization, and optoelectronics devices. During his Ph.D. he has served as a teaching assistant for Contemporary Topics in Photonics, and Semiconductor Epitaxy and Devices.
