Direction-Dependent Homoepitaxial Growth of GaN Nanowires

formation of a fluorescent-dye layer on the surface of porous alumina, the porous alumina substrate was dipped in an ethanol solution containing 20 wt.-% dendrimer [13] and 4 × 10 M pyrromethene 597 (EXITON) for 1 min and then dried. The thickness of the fluorescent-dye layer was approximately 1 lm. Optically pumped lasing experiments were performed using a frequency doubled Nd:yttrium aluminum garnet (YAG) pulse laser (532 nm wavelength, 8 ns pulse width, and 10 Hz repetition rate). The spot size of the incident light was 300 lm. The excitation light from the laser was irradiated from a direction parallel to the cylinder array to the surface of the fluorescent-dye layer. The emission from the cross section of porous alumina cut in the C–X direction was observed using a spectrometer.