This program focuses on the development of a novel class of p-type conductive and highly reflective AlGaN-based distributed Bragg reflectors to enable a host of deep ultraviolet optoelectronic devices, including efficient deep ultraviolet light emitting diodes, vertical-cavity-surface-emitting-lasers, and Fabry-Perot based optical modulators. The proposed project is transformative because it will create the foundations for a new family of efficient deep ultraviolet optoelectronic devices and will usher a host of new industrial applications including water / air / food sterilization and free space communications.
Intellectual Merit: The intellectual merit of the proposed project is the utilization of polarization enhanced ionization of dopants, a unique property to AlGaN alloys, to develop an innovative design of deep ultraviolet distributed Bragg reflectors for a number of optoelectronic devices. The work will also advance the development of AlGaN alloys, which are of great scientific and technological interest.
Broader Impacts: The proposed research promotes the promotion of education through the training of students in a variety of disciplines, ranging from epitaxial growth, to quantum engineering, and semiconductor device physics. To increase the effectiveness and scope of the program, the involvement of undergraduates and high-school interns will be emphasized by taking advantage of several existing channels at Boston University, many of which have a strong focus on the recruitment of underrepresented minorities. Finally, the proposed research will have a strong impact on the environmental and medical sectors, due to specific applications to water / air / food sterilization and for diagnostic and therapeutic uses.
The efficient generation of deep ultraviolet light would have a great societal impact, specifically in regard to water/air sterilization and medical diagnostics and therapeutic technology. The most energy efficient light sources come from solid-state devices such as light emitting diodes (LEDs) and lasers. Solid-state devices operating in the deep ultraviolet regime are made from high Al content AlGaN alloys. Commercial devices are grown on sapphire substrates and typically reach efficiencies of 1-9%. The goal of this project was to develop conductive mirrors to further increase energy efficiency. This is achieved by reflecting light away from absorbing areas of the device (such as contacts) while still providing a path for current to complete the circuit. AlGaN structures were grown using molecular beam epitaxy (MBE). In MBE growth of these alloys, Al, Ga, and N atoms are transported as a vapor or plasma to a heated substrate where the crystallization into AlGaN occurs. During this study the effects of growth parameters such as substrate temperature and incident atom species flux were varied and the effects on conductivity and reflectivity characterized. Using this MBE method, we produced mirrors called distributed Bragg reflectors (DBRs) with approximately 80% reflectivity with 15 layers of AlGaN of various compositional profiles. The electrical properties of these DBRs were modeled and experimentally investigated. Throughout the course of this research, two graduate, two undergraduate, and a high school student were trained in many aspects pertaining to semiconductor technology. Specifically this includes growth by MBE, fabrication technology (plasma etching, metal deposition, and photolithography), and semiconductor characterization techniques (photoluminescence, Hall-Effect measurements, reflectivity, and current-voltage measurements).
