The dependence of External quantum efficiency (EQE) on wavelength for conventional emitters

1. Quasi Equilibrium Crystal Shapes and Kinetic Wulff Plots of Gallium Nitride Grown by Hydride Vapor Phase EpitaxyJames S. Speck, University of California-Santa Barbara, DMR 0906805 Gallium Nitride has become a prominent semiconductor and has opened the door for a new generation of solid state lighting. However, despite the rapid advance in device performance, basic science behind the growth of GaN has lagged. This work demonstrates the quasi equilibrium crystal shape of GaN and the Kinetic Wulff Plots that are derived from the growths by hydride vapor phase epitaxy. GaN was grown on selectively aread masked substrates to demonstrate the growth velocities and thus surface free energy of the facets that emerge during growth. This data can then be used to construct the kinetic wulff plots and demonstrate the slowest growing facets which produce the equilibrium crystal shape. This SEM image shows a GaN crystal that was grown on a selective area sample to demonstrate the shape evolution. The clear facets that emerge present the equilibrium crystal shape under the growth conditions. Semipolar {1011}, nonpolar {1120} and {1010}, and (0001) N-face are observed in these growths Image courtesy Asako Hirai

2. Impact of Nonpolar and SemipolarGaNJames S. Speck, University of California-Santa Barbara, DMR 0906805 UCSB has pioneered new orientations of GaN – namely non basal plane orientations referred to as nonpolar and semipolar planes. These planes offer the promise of high efficiency emitters – particularly in the “green gap” Our fundamental growth studies direct our understanding of optimal nonpolar and semipolar planes. The kinetic Wulff plots reveal the stable growth planes and subtle features of these planes for different growth conditions. The dependence of External quantum efficiency (EQE) on wavelength for conventional emitters and UCSB nonpolar and semipolarGaN. Nonpolar and semipolarGaN provide a pathway to solve the “green gap” in efficiency. The work in the program teaches us the quasi- equilibrium nonpolar and semipolar planes.