Characterization of Hydride Vapor Phase Epitaxy Grown GaN Substrates for Future III-Nitride Growth

The aim of this research is to investigate and characterize the quality of commercially obtained gallium nitride (GaN) on sapphire substrates that have been grown using hydride vapor phase epitaxy (HVPE). GaN substrates are the best choice for optoelectronic applications because of their physical and electrical properties. Even though HVPE GaN substrates are available at low-cost and create the opportunities for growth and production, these substrates suffer from large macro-scale defects on the surface of the substrate. In this research, four GaN on sapphire substrates were investigated in order to characterize the surface defects and, subsequently, understand their influence on homoepitaxial GaN growth. Two substrates were unintentionally doped (UID) GaN on sapphire, and the other two were semi-insulating (SI) GaN on sapphire which were doped with iron (Fe) in order to compensate the background doping inherent in GaN. Several characterization techniques were performed. Atomic force microscopy, scanning electron microscopy, and optical microscopy were performed to characterize the surface morphology. X-ray diffraction, cathodoluminescence, transmission measurements, and optical transmission electron microscopy were applied to study the bulk structural and optical properties. The investigation of the surface of GaN substrates exposed various defects that are associated with defects in the structure such as dislocations, as well as vacancies and point defects. The UID GaN substrates suffered from hexagonal V-shape pits with pits densities of approximately 10 and 10 cm, whereas, the SI GaN substrates exhibited much larger macroscale pits with areal densities of about 10 cm. X-ray diffraction results were deconvoluted in order to characterize the screw and mixed (edge and screw) dislocation densities for the studied substrates. The UID substrates exhibited screw dislocation densities of 10 and 10 cm and mixed dislocation densities of 10 and 10 cm. The SI substrates, however, exhibit generally lower densities of dislocations of 10 and 10 cm for screw and mixed, respectively. Cathodoluminescence measurements demonstrated interesting results for the UID and SI substrates with energies of 4 and 3.5 eV, respectively. The transmission measurements for the UID substrates showed that the bandgap energy was 3.39 eV. Acknowledgements First of all, my deep gratitude to the God who gave me the passion to achieve my ambitions and made me look always forward. He made me always optimistic for the better and confident about my ability and what I can do. My great gratitude to my advisor, Dr. Morgan Ware, who accepted me in his great research group. He is such an amazing advisor who helps and supports his students, and he is very patient with them. He taught me a lot about GaN and semiconductor materials during our discussions. I would like to thank him for providing all materials that I needed in my research and for making it easy to go through. If I did not understand something, I usually asked him, and he explained to me very clearly and guided me in the right direction. This thesis would not be complete without his support, advice, and encouragement. I would like to thank every person in my research group. I would like to thank Pijush Ghosh who helped me from the beginning of my research and training in the labs. I would like to thank him for GaN growth that he did for my research. I would like to thank Alaa Alnami who supported me all the time. I would like to thank Manal Aldawsari for helping me in optical transmission measurements. I would like to thank Mirsaeid Sarollahi who helped and taught me about PL measurements. I would like to thank Reem Alhelais to helped me in cutting the samples. I would like to thank Najla Alnami who supported me in my research. She introduced me to Dr. Ware when I asked to join his group. She always helped me when I discussed with her about semiconductors and physics. I would like to thank Mohammed Alavijeh who usually supported me when I worked in AFM lab. He helped me to get better results. I would like to thank Andrian Kuchuk for x-ray diffraction measurements. Also, I would like to thank Dr. Mourad Benamara and Qigeng Yan for CL and TEM measurements. I am thankful to the director of the Microelectronic-Photonics, Dr. Rick Wise, for his guidance of such an incredible department. He always guides us from the first day in our journey to the last day. He helped me a lot by explaining the rules and providing the information that I needed to graduate. He supported me and encouraged me during my studying. Also, I would like to thank Renee Jones-Hearon who assisted me to do all documents on time. I would like to thank my parents, Amnah and Ahmed, who support me always. I would like to thank them to allow me to travel and achieve my ambitions. I thank them for my education and my encouragement to study since I was a child. They supported me in hard times and contacted me every day to ask about me and my progress. Also, I would like to thank my brother, Hassan, and sister, Nassim, who asked about me and gave me some suggestions to pass through all the hardness. I would like to thank my husband, Alhussain, who supported me and helped me during my graduate study. He helped me a lot during my graduating time to take care of my children, especially my daughter who is two months old. He tried to offer the best environment at home for me, so I could work and did a lot of work. I would like to thank my son, Aseel, and daughter, Nora, for their understanding of my situation. My son helped me to take care of his sister and even he sometimes cooked for me when I missed some meals.