Observing visible-range photoluminescence in GaAs nanowires modified by laser irradiation

摘要

We study the structural and chemical transformations induced by focused laser beam in GaAs nanowires with an axial zinc-blende/wurtzite (ZB/WZ) heterostructure. The experiments are performed using a combination of transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, and photoluminescence spectroscopy. For both the components of heterostructure, laser irradiation under atmospheric air is found to produce a double surface layer which is composed of crystalline arsenic and of amorphous GaO_x. The latter compound is responsible for the appearance of a peak at 1.76 eV in photoluminescence spectra of GaAs nanowires. Under an increased laser power density, due to sample heating, evaporation of the surface crystalline arsenic and formation of /i-Ga_2O_3 nanocrystals proceed on the surface of the zinc-blende part of nanowire. The formed nanocrystals reveal a photoluminescence band in a visible range of 1.7-2.4 eV. At the same power density for wurtzite part of the nanowire, total amorphization with the formation of ß-Ga_2O_3 nanocrystals occurs. Observed transformation of WZ-GaAs to /i-Ga_2O_3 nanocrystals presents an available way for the creation of axial and radial heterostructures ZB-GaAs/ß-Ga_2O_3 for optoelectronic and photonic applications.