• Mumthaz Muhammed, Mufasila

Abstract

III-nitride direct bandgap semiconductors have attracted significant research interest due to their outstanding potential for modern optoelectronic and electronic applications. However, the high cost of III-nitride devices, along with low performance due to dislocation defects, remains an obstacle to their further improvement. In this dissertation, I present a significant enhancement of III-nitride devices based on emerging materials. A promising substrate, (-201)-oriented β-Ga2O3 with unique properties that combine high transparency and conductivity, is used for the first time in the development of high-quality vertical III-nitride devices, which can be cost-effective for large-scale production. In addition, hybridizing GaN with emerging materials, mainly perovskite, is shown to extend the functionality of III-nitride applications. As a part of this investigation, high-performance and high-responsivity fast perovskite/GaN-based UV-visible broadband photodetectors were developed.State-of-the-art GaN epilayers grown on (-201)-oriented β-Ga2O3 using AlN and GaN buffer layers are discussed, and their high optical quality without using growth enhancement techniques is demonstrated. In particular, a low lattice mismatch (⁓4.7%) between GaN and the substrate results in a low density of dislocations ~4.8Å~107 cm−2. To demonstrates the effect of (-201)-oriented β-Ga2O3 substrate on the quality of III-nitride alloys, high-quality ternary alloy InxGa1−xN film is studied, followed by the growth of high quality InxGa1−xN/GaN single and multiple quantum wells (QWs). The optical characterization and carrier dynamics by photoluminescence (PL) and time-resolved PL measurements were subsequently performed. Lastly, to investigate the performance of a vertical emitting device based on InGaN/GaN multiple QWs grown on (-201)-oriented β-Ga2O3 substrate, high-efficiency vertical-injection emitting device is developed and extensively investigated. The conductive nature of the substrate developed as a part of this study yields better current and heat characteristics, while its transparency ensures high light extraction. The straightforward and direct growth process employed does not require a high-cost complex fabrication process.Finally, a broadband photodetector composed of the emerging CH3NH3PbI3 perovskite with the p-GaN, is developed. The findings reported in this dissertation demonstrate the superior performance of CH3NH3PbI3/GaN photodetectors produced by simple and cost-effective solution processed spray-coating method. In particular, it is demonstrated that perovskite/GaN device can work as a self-powered photodetector.

Topics

• density
• perovskite
• impedance spectroscopy
• photoluminescence
• extraction
• semiconductor
• nitride
• dislocation
• coating method