ETY tel: fax: Nanoscale physics of nitride semiconductor heterostructures for electronic and optoelectronic devices Our principal research objective is to elucidate the relationships among nanoscale structural morphology, electronic properties, and device behavior in Group III- nitride semiconductor heterostructures. To this end, proximal probe techniques offer unique capabilities for materials characterization at the nanometer scale. In collaboration with researchers at Emcore/Veeco, we investigated the nanoscale structure of InGaN/GaN quantum-well structures designed for application in visible light emitters, as shown in Figure 1. Researchers at Emcore/Veeco observed that modification of epitaxial growth conditions (“improved” vs. “baseline”) in nominally identical quantum-well structures led to large increases in luminescence efficiency, as shown in Figure 2. Imaging by scanning capacitance microscopy (SCM), as shown in Figure 3, revealed the origin of the increased luminescence efficiency. The “improved” structure exhibited highly localized carrier accumulation, evident as circular features in Figure 3(b), whereas carrier accumulation in the “baseline” structure was much more uniform, as shown in Figure 3(a). Numerical simulations and nanoscale capacitance spectroscopy reveal that this carrier localization occurs in nanoscale In-rich clusters within the quantum-well region, leading to improved radiative recombination efficiency as localized carriers are shielded from defects in surrounding material. These experiments provided direct experimental confirmation of a widely postulated correlation between In clustering and high luminescence efficiency in InGaN/GaN quantum well structures - a topic of considerable controversy within the community of researchers investigating nitride-based light emitters for displays, solid-state lighting, and other applications. Edward T. Yu University of California, San Diego DMR m1m1m1m [X. Zhou, E. T. Yu, D. I. Florescu, J. C. Ramer, D. S. Lee, S. M. Ting, and E. A. Armour, Appl. Phys. Lett. 86, (2005).] Figure 1. InGaN/GaN quantum-well structure for visible (green) LED, and experimental geometry for SCM measurement. Figure 2. Room-temperature photoluminescence spectra, revealing increased luminescence efficiency in “improved” vs. “baseline” sample. (a)(b) Figure 3. SCM images of (a) “baseline” and (b) “improved” structures, revealing localized carrier accumulation in “improved” structure correlated with increased luminescence efficiency. Research

ETY tel: fax: Nanoscale physics of nitride semiconductor heterostructures for electronic and optoelectronic devices Our education and outreach efforts incorporate, among other activities, participation in a yearly offering of a Freshman Seminar in Electrical and Computer Engineering at UCSD. Each year, the seminar focuses on different aspects of electronics, photonics, and related technologies and their impact on students’ everyday lives. Shown at right is the PI teaching of a Freshman Seminar class in April The topic for this lecture was “Why Size Matters: What is Nanotechnology and Why Is It Different?” Graduate students involved in this project are active participants as mentors to secondary school students from the UCSD Preuss School. The Preuss School is a San Diego charter school targeting underprivileged, high-potential students from the San Diego Unified School District. UCSD students act as mentors to Preuss School students, providing tutoring, academic and career advice, and guidance in extracurricular activities. Shown at right is a graduate student from the PI’s laboratory, Sourobh Raychaudhuri, assisting a Preuss School student in his studies. Edward T. Yu University of California, San Diego DMR PI Edward Yu teaching a Freshman Seminar class at UCSD. Graduate student researcher Sourobh Raychaudhuri assisting a student at the UCSD Preuss School in his studies. Education and Outreach