Phase Transformation in Radially Merged Wurtzite GaAs Nanowires.
III-V Nanowires (NWs) grown with metal-organic chemical vapor deposition commonly show a polytypic crystal structure, allowing growth of structures not found in the bulk counterpart. In this paper we studied the radial overgrowth of pure wurtzite (WZ) GaAs nanowires and characterized the samples with high resolution X-ray diffraction (XRD) to reveal the crystal structure of the grown material. In particular, we investigated what happens when adjacent WZ NWs radially merge with each other by analyzing the evolution of XRD peaks for different amounts of radial overgrowth and merging. By preparing cross-sectional lamella samples we also analyzed the local crystal structure of partly merged NWs by transmission electron microscopy. Once individual NWs start to merge, the crystal structure of the merged segments is transformed progressively from initial pure WZ to a mixed WZ/ZB structure. The merging process is then modeled using a simple combinatorial approach, which predicts that merging of two or more WZ NWs will result in a mixed crystal structure containing WZ, ZB, and 4H. The existence large and relaxed segments of 4H structure within the merged NWs was confirmed by XRD, allowing us to accurately determine the lattice parameters of GaAs 4H. We compare the measured WZ and 4H unit cells with an ideal tetrahedron and find that both the polytypes are elongated in thec-axis and compressed in thea-axis compared to the geometrically converted cubic ZB unit cell.
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden.
Daniel
D
Jacobsson
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden.
Fangfang
F
Yang
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden ; AZUR Space Solar Power GmbH , Theresienstrasse 2, 74072 Heilbronn, Germany.
Karla
K
Hillerich
nCHREM/Centre for Analysis and Synthesis, Lund University , Box 124, 221 00 Lund, Sweden.
Filip
F
Lenrick
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden.
Sebastian
S
Lehmann
Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenbergerstrasse 69, A-4040 Linz, Austria ; Department of Condensed Matter Physics, Charles University in Prague , Ke Karlovu 5, 121 16, Praha 2, Czech Republic.
Dominik
D
Kriegner
Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenbergerstrasse 69, A-4040 Linz, Austria.
Julian
J
Stangl
nCHREM/Centre for Analysis and Synthesis, Lund University , Box 124, 221 00 Lund, Sweden.
L Reine
LR
Wallenberg
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden ; nCHREM/Centre for Analysis and Synthesis, Lund University , Box 124, 221 00 Lund, Sweden.
Kimberly A
KA
Dick
Solid State Physics/The Nanometer Structure Consortium, Lund University , Box 118, 221 00 Lund, Sweden.
Jonas
J
Johansson