Charge carrier dynamics under the influence of extreme strain gradients realized in bent semiconductor nanowires

The quasi-one-dimensional nature and remarkable flexibility of semiconductor nanowires (NWs) unlock new possibilities in strain engineering, enabling the tailoring of electronic properties through the introduction of high strain gradients. In this study, we systematically investigate the effects of inhomogeneous strain on the electronic transitions of bent GaAs NWs. Taking advantage of the flux directionality and high crystal quality achieved through molecular beam epitaxy (MBE), high-phase-purity GaAs NWs are fabricated and bent through the growth of an In0.5Al0.5As asymmetric stressor shell, which introduces a substantial lattice mismatch (≈3.6%). The bending is designed using an analytical elastic model that predicts the curvature based on shell thickness and cross-sectional geometry. To refine the model’s accuracy and deepen our understanding, plan-view transmission electron microscopy (TEM) is employed to characterize the bent NWs, providing valuable insights into the growth kinetics of the asymmetric shell. The systematic fabrication of bent NWs facilitates the investigation of their electronic transitions through photoluminescence (PL) spectroscopy, using the clean spectra of zinc-blende GaAs NWs prior to bending as a reference. This baseline is crucial for analyzing bending effects. The inhomogeneous strain is investigated by considering deformation potential interactions, piezoelectric fields, and the previously unexplored flexoelectricity in GaAs. Our findings reveal the presence of electric fields in all bent NW samples, expanding the understanding of inhomogeneous strain effects. To advance strain engineering, we develop a one-dimensional model that accounts for deformation potential, piezoelectricity, and flexoelectricity, which calculates electronic transition shifts based on NW diameter and curvature. These calculated shifts are consistent with the trends observed in our PL experimental data. We further discuss the limitations of this model by comparing it with results from finite element method (FEM) simulations of piezoelectric potential.