Plan-view transmission electron microscopy investigation of GaAs/(In,Ga)As core-shell nanowires

摘要

Plan-view transmission electron microscopy in combination with electron energy-loss spectroscopy have been used to analyze the strain and the chemical composition of GaAs/(In,Ga)As core-shell nanowires. The samples consist of an GaAs core and a radially arranged (In,Ga)As layer as quantum well and GaAs outer-shell. The nominal parameters of the quantum well in the two samples under investigation are: an indium concentration of 25% and a quantum well thickness of 22 nm and 11 nm, respectively, while the core and the external shell dimensions are fixed. Scanning transmission electron microscopy using high-angle annular dark field detector was performed to verify the actual dimensions of the layers. Geometric phase analysis was carried out in order to examine the local strain of the radial (In,Ga)As quantum well, while the local chemical composition was determined by means of spatially resolved electron energy-loss spectroscopy. Finite elements calculations were carried out in order to simulate the multi-shell structure and extract the actual strain distribution. The results indicate that there is a uniform strain distribution at the coherent interfaces. In addition, based on calculations, we show that there is no region in the considered core-shell structure absolutely free of strain.