Photocurrent Enhancement by Surface Plasmon Resonance of Gold Nanoparticles in Single Gallium Nitride Nanowires

This dissertation presents the study on the electron transport properties of individual gallium nitride (GaN) nanowires grown by a vapor liquid solid (VLS) process. Conductive atomic force microscopy (C-AFM) and two-probe methods has been used to investigate the variation in electrical conductance of GaN nanowires as a function of nanowire length (5 mum to 40 mum), nanowire diameter (80 nm to 400 nm) and gold (Au) nanoparticle decoration on the surface of nanowires. We also report the photoconducting and photo-excitation properties of individual GaN nanowires and examine the influence of nanowire dimensions and Au nanoparticle decoration with respect to different wavelength of laser light (405 nm (blue), 532 nm (green), and 632.8 nm (red)) used. Standard photolithography techniques are applied to pattern the two-point Cr/Au (50 run/ 150 nm) electrodes on single GaN nanowires lying on SiO2 substrate. Experimental results demonstrated the deviation in electrical properties of individual GaN nanowires due to nanowire geometry, surface modification and light exposure in the visible range. Photoresponse of bare GaN nanowires as a function of nanowire diameter and a constant laser power (10mW/cm2), increase smoothly with increasing diameter and from longer to shorter wavelengths of light. In the case of Au/GaN nanowires, the enhancement in photocurrent is effectively equivalent to the values obtained prior to metallization for diameters less than 200 nm. Above a critical diameter of ~200nm the photocurrent of Au/GaN nanowires exhibit diameter dependent enhancement of 100% to 500% larger than their dark current values. Time dependent photocurrent measurements revealed a faster response time in Au/GaN nanowires compared to the bare GaN nanowires, which make them suitable candidates for opto-electronic switches. This study will have a far reaching impact on the development of nanophotonic devices and will stimulate further research on the rapidly developing field of surface plasmon nanophotonics.