Critical dimensions in coherently strained coaxial nanowire heterostructures

Abstract

Articles you may be interested inFerromagnet-semiconductor nanowire coaxial heterostructures grown by molecular-beam epitaxy Appl. Phys. Lett. 95, 133126 (2009); 10.1063/1.3240405 Strain distribution and interface modulation of highly lattice-mismatched InN/GaN heterostructure nanowires Appl. Phys. Lett. 95, 033112 (2009);We present a methodology to determine critical dimensions for coherently strained coaxial nanowire heterostructures based on a well-known formalism used to determine the critical thickness in planar epitaxial growth. The unique geometry of the nanowire structure along with the volumetric similarity of the core and shell regions give rise to a number of possible stable core-shell configurations for a given choice of materials. We show that a unique critical core radius and critical shell thickness, dependent on core radius, can quantify these configurations. Illustrative calculations are presented for various nitride semiconductor-based core-shell structures. It is anticipated that this model will serve as a guide to determine the feasibility of specific coherently strained nanowire heterostructure designs.

Faster radial strain relaxation in InAs–GaAs core–shell heterowires

“…Such three-dimensional geometries dramatically modify the theoretical critical thresholds for strain relaxation. [4][5][6][7][8][9] For nanowire core diameters below critical thresholds, the volume strain energy is too small for dislocations, meaning coherent axial or core-shell geometries are theoretically feasibly consistent with experimental observations. 10 Barriers to the nucleation of misfit dislocations have often resulted in larger critical thicknesses in planar systems, 11 also likely true for nanowires.…”

“…17 Wurtzite phase heterowires with preferred growth directions (001) and hexagonal sidewall facets were investigated. The radii of the InAs cores (11-26 nm) all exceeded theoretical critical core radii values (>2 nm) 8 with GaAs shell thicknesses greater than 2.5 nm. Strain relaxation via dislocations was observed with the degree of radial relaxation in most cases, greater than axial strain relaxation.…”

“…Calculations conflict as to which direction should relax first. 4,7,8 The percentage axial strain relaxation of the WZ wires increased exponentially with shell thickness (normalized to the core size) more slowly than radial strain relaxation, which was comparably more abrupt. Extrapolation indicated a critical shell-to-core ratio for axial strain relaxation at these core radii of 0.1.…”

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

“…5 In addition, the band gap of the InAs shell as well as that of the GaAs core close to the heterointerface will be significantly influenced by strain due to the large lattice misfit between the two materials. 35,36 We calculated the strain distribution of our GaAs/InAs core/shell NWs, the resulting band alignment around the heterointerface, and the confinement energy for electrons in the InAs shell in terms of linear elasticity theory. Since the shell layer is 2 nm thick and the NW core has a diameter of 86 nm, we could not do a full 3D modelling due to limitations in computer power.…”

III-Nitride quantum dots in nanowires: growth, structural, and optical properties

“…Accordingly, it is theoretically predicted that the formation of fully strained axial and core-shell NW heterostructures should be observed in a wide range of lattice mismatch values [12][13][14]. Recently, it has been further shown for axial heterostructures that depending on in-plane lattice mismatch and NW diameter, the growth of disks could be favored with respect to the formation of 3D islands [15].…”