J. Walia, N. Dhindsa, J. Flannery, R. LaPierre, J. Forrest, S.S. Saini
University of Waterloo, Canada
pp. 32 - 33
Keywords: gallium arsenide, nanowires, Raman spectroscopy, photothermal
The structural and optical changes in vertically etched GaAs nanowires are examined. The nanowires were annealed via photo-thermal conversion, using 100 mW of incident laser power, to induce the onset of arsenic formation. Four nanowire diameters of 65 nm, 155 nm, 200 nm, and 245 nm, arranged in square lattices spaced 400 nm apart, were studied. Annealing temperatures were found be dependent on nanowire diameters, ranging from 480 K to 700 K, resulting from the different degrees of optical confinement in each sample. The presence of As was confirmed using Raman spectroscopy. It was found that all diameters exhibited photothermal formation of crystalline arsenic (c-As), even for annealing temperatures as low 480 K, suggesting the temperature required for c-As formation in GaAs nanowires is reduced relative to the bulk by about ~ 220 K. The salient changes in structural color generation properties resulting from the annealing process are easily seen using an optical microscope, whereas no changes of any kind are seen with scanning electron microscopy. In this connection, color generation properties of GaAs nanowire arrays can be locally tuned using a laser, and the onset of these changes are initiated at lower temperatures than expected.