ETY 2006 [email protected] http://nanolab.ucsd.edu tel: +1.858.534.6619 fax: +1.858.822.3425 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. YuUniversity of California, San Diego DMR- 0405851 1m 1m [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, 202113 (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