Crystal-structure-dependent photoluminescence from InP nanowires

The formation and photoluminescence (PL) of InP nanowires grown by metal organic vapour phase epitaxy on InP(1 1 1)B substrates, using colloidal gold nanoparticles as catalysts, are investigated. The dependence of the orientation and dimensions of the nanowires on the growth temperature is studied using scanning electron microscopy. Vertically aligned < 1 1 1 > oriented nanowires with a mean base diameter in the range 50-150 mu m, and a tip diameter of 50 nm, show a PL blue-shift of about 80 meV compared to the substrate. Blue-shift due to quantum confinement is ruled out because of the large diameter of the nanowires. A clear correlation between the orientation of the nanowires on the substrate and the PL peak position is observed. Based on x-ray diffraction and transmission electron microscopy measurements, it is proposed that the as-grown vertically oriented nanowires have crystallized in the wurtzite lattice instead of in the zinc-blende structure, which results in a blue-shifted PL.