Kansas State University

1. III-Nitride Deep Ultraviolet Photonic Materials and Structures Jingyu Lin & Hongxing Jiang DMR-0504601  Kansas State University Identification of cation vacancies and complexes in AlGaN alloys • High quality and highly conductive AlxGa1-xN alloys with x > 0.5 are needed to achieve optoelectronic devices active in the deep ultraviolet region ( < 300 nm). Achieving highly conductive AlxGa1-xN alloys with high Al content has been very challenging. It is known that the presence of cation vacancies in AlxGa1-xN reduces n-type conductivity because cation vacancies act as compensating centers (or deep level acceptors) for n-type dopants. However, identification of cation vacancies in AlGaN has been difficult. • By employing deep ultraviolet (UV) photoluminescence (PL) spectroscopy, we have identified two different deep level acceptors in AlxGa1-xN alloys: isolated cation vacancies (Vcation) with 3-negatively charged state and Vcation-complexes with 2-negatively charged state. These acceptor levels are pinned to two different energy levels universal to AlxGa1-xN alloys (0  x 1). The presence of prominent cation vacancy related emission peaks in Al-rich AlxGa1-xN alloys directly translates to reduced conductivities and thus the UV PL technique can be utilized for material and layer structural optimization. • Much work remains to be done to enhance p-type doping efficiency in Al-rich AlGaN alloys. Figure description: Deep acceptor (cation vacancies) energy levels (EA) as functions of x in AlxGa1-xN alloys, obtained from PL measurement. Ec and Ev are also included with ED0 being the shallow donor level. The valence band maximum of GaN is chosen as E=0. The well known yellow-line (YL) in GaN and violet-line (VL) in AlN are also indicated.

2. III-Nitride Deep Ultraviolet Photonic Materials and Structures Jingyu Lin & Hongxing Jiang DMR-0504601  Kansas State University Reaching out to local school kids The P.I. (Lin) of this project serves as a faculty advisor for the Woman in Engineering and Science Program (WESP) at Kansas State University. WESP provides outreach, recruitment, and programs for girls and women from middle school through post-graduate levels, to encourage them to consider and persist in careers in science, mathematics and engineering. Prof. Lin conducts demonstrations on LEDs, lasers and optical effects in local schools several times a year in order to reach out to the broader community. The PI’s lab is a “hot” spot for illustrating “Science in Action” to local students. She also participates in a yearly university open-house demonstrating progress in III-nitride photonic devices through NSF supported materials research. Figure description: “It’s so cool! How did you do that?” Visitors from a local school observing a blue light emitting “wild-cat” - Kansas State University logo fabricated in the P.I.’s lab.