Poster Presentation 26th ACMM “2020 Visions in Microscopy”

Effects of Twinning Density on Optical properties of GaAs Nanowires (#235)

Zahra Azimi 1 , H H Tan 1 , C Jagadish 1 , J Wong Leung 1
  1. Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Acton, Australian Capital Territory, Australia

The possibility of designing composite Gallium-Arsenide (GaAs) nanowires structures via bottom-up methods has attracted significant interest for the engineering of future optoelectronic devices [1]. The crystal structure and the stacking fault density of GaAs nanowires  largely determine their optoelectronic properties [2]. Here, we present an investigation of the structural and optical properties of GaAs nanowires. GaAs nanowires were grown by metalorganic vapour phase epitaxy (MOCVD) on GaAs (111)B substrates, prepared via selected area epitaxy (SAE). Transmission electron microscopy (TEM) shows that GaAs nanowires have a ZB structure with a varying twin defect density (TDs) along the nanowire’s length. Dark field TEM images along the nanowires shows that the average local twin defect density (ntdd), computed for a section length of 1 um along the NW’s axis, decreases from 110 to 13 #/µm from the base to the tip of the NW. To correlate the GaAs NW crystal structure to its electronic band structure, cathodoluminescence (CL) and time resolved photoluminescence measurement were done at room temperature. The CL intensity increases by 14 times from the bottom to the NW’s tip, while the CL peak position shifted from 897 nm (1.382 eV) to 886 nm (1.399 eV). The CL peaks red-shift along the NWs vertical axis is tentatively attributed to type-II band alignment at the ZB-TD-ZB interfaces. The high surface recombination velocity of GaAs is a major issue for their use in optoelectronic devices. As a result, passivation of the nanowire surface is required for various applications such as lasing. Here, however, we demonstrate that when sufficient nanowire’s length and optimal structural properties are obtained, pure unpassivated GaAs nanowires can achieve low-temperature lasing. This provides insights toward the engineering of GaAs NW properties for their use in devices.

 

 

[1]       B. Ketterer, M. Heiss, E. Uccelli, J. Arbiol, and A. Fontcuberta I Morral, ‘Untangling the electronic band structure of wurtzite GaAs nanowires by resonant Raman spectroscopy’, ACS Nano, vol. 5, no. 9, pp. 7585–7592, 2011.

[2]       R. E. Algra et al., ‘Twinning superlattices in indium phosphide nanowires’, Nature, vol. 456, no. 7220, pp. 369–372, 2008.