Freestanding semiconductor nanowires have been explored for a wide range of next-generation optoelectronic devices and sensors, where the unique nanowire shape and mechanical flexibility has enabled highly lattice-mismatched heterostructures and novel device geometries. Along these lines, spontaneous bending in asymmetric core−shell nanowire heterostructures has opened up possibilities for novel strain-gradient engineering and new bottom-up device fabrication approaches. Strain gradients—which cannot be realized in conventional planar heterostructures grown on bulk substrates—can be employed to control the motion of charge carriers, which can be utilized to improve light emission from nanowire heterostructures. The synthesis of spontaneously bent nanowires makes use of the nanowire shape and the directionality of the shell deposition process. However, both the synthesis and device possibilities of bent nanowire heterostructures remain underexplored.

In this presentation, we explain the underlying mechanisms governing the synthesis of bent nanowire heterostructures by molecular beam epitaxy. We show that the bending process leads to large local variations in nanowire shell thickness, bending and strain, along the length of the nanowire. Photoluminescence spectroscopy on bent-nanowire heterostructures demonstrates that spatially varying strain fields induce charge carrier drift toward the tensile-strained outside of the nanowires. The strain gradient is employed for light emission by placing an active region of quantum dots at the outer side of a bent nanowire to exploit the resulting carrier drift, increasing the emission from the quantum dots by an order of magnitude compared to straight nanowires. In another application of bent nanowire synthesis, deposition shadowing by neighboring nanowires is explored and used to connect nanowire pairs. These novel nanowire pair nanostructures are of high interest for nanowire sensors. A novel nanowire pair sensor—with a controllable bottom-up fabrication process—is presented.