Advanced architectures of GaN-based light-emitting devices from blue to UV

• Main Author: Zheng, Haiyang
• Other Authors: Hilmi Volkan Demir
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/142747
• Institution: Nanyang Technological University

In the past few decades, remarkable progress has been made in the research and development of gallium nitride (GaN)-based light sources. Among them, GaN-based blue and ultraviolet (UV) light-emitting diodes (LEDs) have achieved great success and attracted considerable attention in a wide range of applications. GaN-based blue LEDs are highly efficient and reliable visible light sources, and thus have found broad applications in solid-state lighting (SSL), automobile headlights, LED displays, liquid crystal display (LCD) backlights, flash units, and compact projectors and scanners. Also, GaN-based UV LEDs are energy efficient and robust UV light sources, and they have great potential in UV curing, counterfeit detection, UV lithography, photocatalysis, air purification and tanning (UV-A or near-UV), medical phototherapy, protein analysis and drug discovery (UV-B), water/air disinfection, and bioagent-sensing (UV-C or deep-UV). In this thesis, leveraging on the GaN-based blue LED materials and device platform that we developed, we extended our work beyond the visible and ventured into the deep-UV. In this thesis, we have successfully developed and established the GaN-based UV LED materials and devices platform, which allows us to grow high-quality GaN-based epitaxial wafers and demonstrated state-of-the-art devices with lateral, flip-chip and vertical architectures. Leverage on this platform, various structures have been designed, grown and fabricated to enhance the performance of InGaN/(Al)GaN blue and near-UV LEDs. In one of the important works, we have designed the near-UV micro-LEDs to enhance the efficiency and reduce the efficiency droop. In a separate work, the low confinement capability of near-UV multiple quantum wells (MQWs) and thus low carrier injection has been alleviated by raising the barrier height of the quantum barriers of our LEDs. We have also explored the possibility of pumping the MQWs using e-beam and demonstrated the e-beam pumped UV CL structures. Moreover, we have extended our research from near-UV to deep-UV CL structures based on e-beam pumping. The findings of this thesis from blue to UV contribute to both materials level and device level understanding of III-N material systems and device platforms for applications ranging from artificial lighting to curing and disinfection.