Counterintuitive strain distribution in axial (In,Ga)N/GaN nanowires

TL;DR

This study reveals unexpected strain behavior in axial (In,Ga)N/GaN nanowires, showing large negative out-of-plane strains due to free sidewall deformation, with implications for experimental strain assessment.

Contribution

It uncovers a counterintuitive strain distribution in nanowires and links it to deformation at sidewalls, using finite element simulations within linear elasticity theory.

Findings

Large negative out-of-plane strain occurs near segment length-to-radius ratio of one.

Deformation at free sidewalls causes significant shear strain components.

Reciprocal space maps can experimentally detect this strain state.

Abstract

We study the three-dimensional deformation field induced by an axial (In,Ga)N segment in a GaN nanowire. Using the finite element method within the framework of linear elasticity theory, we study the dependence of the strain field on the ratio of segment length and nanowire radius. Contrary to intuition, the out-of-plane-component of the elastic strain tensor is found to assume large negative values for a length-to-radius ratio close to one. We show that this unexpected effect is a direct consequence of the deformation of the nanowire at the free sidewalls and the associated large shear strain components. Simulated reciprocal space maps of a single (In,Ga)N/GaN nanowire demonstrate that nanofocus x-ray diffraction is a suitable technique to assess this peculiar strain state experimentally.