Efficient methodology to correlate structural with optical properties of GaAs nanowires based on scanning electron microscopy

Abstract

Twin boundaries and boundaries between zincblende (ZB) and wurtzite (WZ) segments of GaAs-related nanowires (NWs) form intrinsic heterointerfaces with essential consequences for the application of such nanomaterials in optoelectronic devices. We show that for GaAs and GaAs/(Al, Ga)As core/shell NWs, crystal twinning along the NW axis can be imaged with a spatial resolution of 10 nm using secondary electrons in a scanning electron microscope (SEM). Changes of the crystal structure from the ZB to the WZ phase have been investigated by electron backscatter diffraction. In addition to these methods, we employ spectrally and spatially resolved cathodoluminescence measurements in the same SEM to study the correlation between the structural and optical properties in single NWs. Two GaAs/AlAs/GaAs core/shell/shell NWs differing significantly in the crystal structure along their axis have been investigated combining these three techniques in order to demonstrate the strength of the employed methodology. Our experiments show that based on commonly available SEM methods, an overview of the structural properties along an entire NW and their impact on the spectral and spatial luminescence distribution can be efficiently obtained providing a quick feedback for the optimization of growth conditions.

Correlated Nanoscale Analysis of the Emission from Wurtzite versus Zincblende (In,Ga)As/GaAs Nanowire Core–Shell Quantum Wells

“…EBSD in an SEM allows the determination of the crystal polytype of extended segments in GaAs NWs . To this end, a Zeiss Ultra 55 field-emission SEM equipped with an EDAX/TSL EBSD system was operated at an acceleration voltage of 20 kV and a beam current of 1.7 nA.…”

“…EBSD in an SEM allows the determination of the crystal polytype of extended segments in GaAs NWs. 62 To this end, a Zeiss Ultra 55 field-emission SEM equipped with an EDAX/TSL EBSD system was operated at an acceleration voltage of 20 kV and a beam current of 1.7 nA. NWs were dispersed on a Si substrate covered with Au-markers to facilitate subsequent CL measurements on the same NW.…”

Correlated Electro-Optical and Structural Study of Electrically Tunable Nanowire Quantum Dot Emitters

“…The seminal work of Bao et al correlated the optical and structural properties of rotationally twined InP nanowires, combining photoluminescence (PL) and TEM . Several reports followed, mainly correlating PL or cathodoluminescence (CL) with scanning transmission electron microscopy (STEM) in various nanowire systems, with particular effort devoted to the study of polytypism in nanowires. − Correlated studies on the same nanowire were also performed for transport measurements, with a pioneering article by Peng and co-workers demonstrating that the conductive behavior (metallic or semiconductor) of In 2 Se 3 nanowires depends on the crystallographic growth direction . Other demonstrations of correlated structural and transport studies include, for instance, mechanical bend test, transport, and high-resolution TEM on an individual Nb 2 O 5 nanowire or phototransport measurements correlated with high-angle annular dark field (HAADF) STEM on axial GaN/AlN heterostructured nanowires …”

Carrier diffusion in GaN -- a cathodoluminescence study. I: Temperature-dependent generation volume

“…SEM is thus well suited and often the method of choice for the fabrication and investigation of nanostructures [3]. For a comprehensive physical and chemical characterization of these structures, various analytical techniques can be combined in a single instrument, such as secondary and backscattered electron imaging, electron backscatter diffraction, cathodoluminescence spectroscopy (CL) and energy dispersive x-ray spectroscopy (EDX) [4,5]. A spatial resolution corresponding to the minimum diameter of the focused electron beam can, however, only be achieved for secondary electron imaging.…”