Absorption spectroscopy and time-resolved photoluminescence in wedge-shaped nanowalls of GaN.

Wedge-shaped c-GaN nanowall networks grown on c-sapphire substrates are found to show significant blue shift and broadening of the band-edge feature in photoluminescence (PL) spectra. Electron mobility in these structures has also been estimated to be much higher than the theoretical mobility limit in GaN for the same concentration of electrons. These findings suggest quantum confinement of the electrons in the system. Such a confinement has been theoretically explained in terms of the accumulation of negative polarization charges at the inclined facets of the nanowedges that force the free electrons in the conduction band to assemble at the central vertical plane of the structure. If such a triangular confining potential at all exists, the carrier recombination rate is expected to be reduced due to the movement of the photogenerated electrons and holes in opposite directions. Here, we have carried out time-resolved photoluminescence measurements at different transition energy points on a nanowedge-network and a continuous c-GaN epitaxial film grown on c-sapphire substrates. Our study reveals slower PL decay time for the network sample as compared to the continuous film that supports the theoretical model. [ABSTRACT FROM AUTHOR]