Analysis of Critical Dimensions for Nanowire Core-Multishell Heterostructures

Abstract

Critical dimensions for nanowire core-multishell heterostructures are analyzed by using finite-element method based on the energy equilibrium criteria. Results show that the nanowire core-shell heterostructure can sufficiently reduce the strain in the shell and increase the critical shell thickness. The critical dimensions for the nanowire core-multishell heterostructure are determined by the stress fields generated at two heterointerfaces. For thin barrier, the critical dimensions decrease as the core radius increases, while when the barrier is thick enough, the critical dimensions show an increase with the increase of core radius conversely. This can be attributed to a competition between the lattice mismatch and strain distribution, which dominate the critical dimensions alternatively. Two critical quantum well thicknesses are obtained in the nanowire core-multishell heterostructure. Below the dislocation-free critical thickness, the structure will be coherent regardless of the barrier thickness. While above the dislocation-unavoidable thickness, dislocations are always energetically favored. In the dislocation-controllable region between the two critical thicknesses, coherent structure can be obtained via controlling the well and barrier thicknesses. The results are in good agreement with the experimental data and may serve as guidance for the design of coherent nanowire core-multishell quantum well structures and devices.

X-ray Bragg Ptychography on a Single InGaN/GaN Core–Shell Nanowire

“…Due to significant thickness of the epitaxial shell, misfit dislocations play a major role in strain relaxation process. Following theoretical predictions, − the critical thickness of the shell in core–shell NWs does not exceed 20 nm for the core with a diameter of 340 nm. Therefore, the relaxation of misfit strain via dislocations has to be considered.…”

Growth and Strain Relaxation Mechanisms of InAs/InP/GaAsSb Core-Dual-Shell Nanowires

“…Semiconductor nanowires (NWs) can be used as building blocks for electronic and photonic devices and sensors due to their unique properties, such as high surface-to-volume ratio, free-standing nature, and capability to relax elastic stress in two dimensions . One of the most appealing NW features is the possibility to create heterostructures by combining different materials in both axial and radial directions. , In recent years, researchers have been paying much attention to the so-called core–shell (CS) NWs because radial geometry can improve the performance and/or add new properties in the devices. , For example, surface passivation by the introduction of one or more shells around the core can enhance the radiative emission efficiency, reducing the carrier surface recombination . Many core–shell NWs based on III–V semiconductors have been demonstrated: InAs/InP, InAs/GaAs, InAs­(Sb)/GaSb, InAs/GaSb, and GaAs/GaSb .…”

“…2,3 In recent years, researchers have been paying much attention to the so-called core−shell (CS) NWs because radial geometry can improve the performance and/or add new properties in the devices. 4,5 For example, surface passivation by the introduction of one or more shells around the core can enhance the radiative emission efficiency, reducing the carrier surface recombination. 6 Many core−shell NWs based on III−V semiconductors have been demonstrated: InAs/InP, 7 InAs/GaAs, 8 InAs(Sb)/GaSb, 6 InAs/GaSb, 9 and GaAs/GaSb.…”

3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells

“…As discussed previously, there is no general model that predicts when dislocations will form or what types of dislocations are most probable for core–shell NW heterostructures. ,, Qualitatively, defect formation is dependent on the core diameter, shell and barrier thicknesses, and lattice mismatch (In content). Yan et al considered the formation of a dislocation loop and predicted critical InGaAs QW thicknesses for cylindrical NWs with core/barrier thicknesses similar to those studied in this work (100 nm GaAs core and 50 nm GaAs barrier). Their model predicts a critical QW thickness of ∼23 nm at a 20% In content.…”

“…Theory and modeling have played important roles in understanding and predicting the onset of defect formation in core–shell heterostructures. − One key finding is that the theoretical critical layer thickness in the shell of NWs is increased compared to planar structures for two reasons. First, the coaxial geometry of NWs enables enhanced strain relaxation parallel to the growth interface, which increases in area with time.…”