The objective of this research is to develop a super-atmospheric-pressure MOCVD (metal-organic chemical vapor deposition) epitaxial deposition system for group-III nitride semiconductor materials. Such a system does not presently exist in the United States. III-nitrides are of interest as critical active materials optoelectronic devices (light emitting diodes, laser diodes, and solar cells) and transistors. The development complements ongoing investment at UNC Charlotte.
The intellectual merit is in enabling basic research on III-nitride optoelectronic materials, and through understanding of connections between device performance, material properties, defect formation, and growth conditions. The track record of participants is excellent and adequate resources are in place for conducting this work. The proposed research is not incremental but fundamental in the study of ultra-low defect material growth. A proposed photoluminescence system will provide a means for quantitative analysis of radiative efficiency of semiconductor materials.
The broader impact of this program is to provide unique optoelectronic heterostructures to many device researchers including: (1) UNC Charlotte faculty and students in several departments, (2) selected high school student interns through established UNC Charlotte programs, (3) businesses operating within the Charlotte Research Institute, and (4) as part of the Optics User Facilities, faculty and researchers at other institutions. Students will benefit by directly operating the reactor, and also by fabricating devices using novel materials provided. Societal impact is considerable, through increased lighting efficiency and improved solar cell technology.
Over the period 2008-2013, the National Science Foundation (NSF) provided funding for design and construction of a new electronic material manufacturing system to the research group of Professor Edward Stokes in the Department of Electrical and Computer Engineering (ECE) at the University of North Carolina at Charlotte (UNCC). This project was funded through the NSFâ€™s Major Research Instrumentation (MRI) program and was entitled "MRI: Development of a high-pressure MOCVD for III-nitride semiconductor devices". Over the last 15 years, first at General Electric, then at UNCC, Professor Stokes has been involved in development of electronic devices which are useful for high efficiency lighting. Since about 25% of electricity is used for lighting, higher efficiency light sources save electricity, and reduce the amount of fossil fuels that are burned to make electricity. The highest efficiency light sources currently available are made from semiconductor light emitting diodes (LEDs). The first generation of LED light bulbs are now commonly available and many citizens and businesses are using them for general illumination. However, there are still improvements to be made. Semiconductor materials for LED lighting are typically manufactured using a process called MOCVD. Many scientists believe that if MOCVD was used at higher pressure, it would be possible to expand the range of colors available from LEDs and therefore to make even higher efficiency LED light bulbs. So the NSF MRI project at UNC Charlotte was focused on design, construction, and commissioning of a high pressure MOCVD system. At this time, the system is operational and Professor Stokes is working with his students and with industrial partners to use the system to improve electronic materials for LED lighting and also for solar cells. Over the course of this project many students, faculty, and industrial partners have been involved in this project. Professor Mesbah Uddin and his student Mr. Phill Davis used advanced software from the automotive industry to simulate the operation of the high pressure MOCVD. Mr. Davis joined the project first as an undergraduate Mechanical Engineering (ME) student under an NSF Reseach Experience for Undergraduates (REU) program, then later continued after being selected for an NSF Ph.D. fellowship. The detailed construction and commissioning of the reactor was coordinated and supervised by Professor Stokes, along with post-doctoral researcher Dr. Andrew Melton. The software to operate the reactor was developed over two summers by undergraduate REU Computer Engineering student Hosman Martinez. Two other REU students from ECE, Mr. Matthew Conway and Mr. Danny Fullager, assisted with the construction and commissioning of the reactor Ph.D. student Mr. Cheng Li developed a custom microscope which is used to evaluate materials from the high pressure MOCVD. Mr. Li was partially supported by grants from industrial partner Veeco Turbodisc, a major manufacturer of MOCVD equipment. Veeco also provided advice and consulting over the course of the MOCVD design and construction, and they provided numerous samples of useful starting materials to the program The high pressure MOCVD system is now fully operational and available for usage by the faculty and students of UNC Charlotte and their research partners from government, industry, and other academic institutions. Finally, the high pressure MOCVD is used routinely as an educational tool. Dr. Stokes and Dr. Melton developed a special series of lecture and laboratory work for Dr. Stokes "Fabrication of Nanomaterials" class which is taught each spring at UNC Charlotte. In this interdisciplinary class, Ph.D. students from engineering, chemistry, and physics learn about LED lighting and participate in the manufacture and analysis of custom electronic materials using the high pressure MOCVD system.