Electric-Field-Assisted Phase Switching for Crystal Phase Quantum Dot Fabrication in GaAs Nanowires

The occurrence of several crystal phases within the nanostructures of a single material presents both challenges and opportunities. While unintended phase mixing can degrade optoelectronic performances, deliberate control of polytypism enables heterostructures with unique quantum properties, such as crystal phase quantum dots (CPQDs). However, since tailoring the formation of CPQDs is difficult, applications remain scarce. Here, we demonstrate electric-field-driven crystal phase switching in GaAs nanowires during vapor-liquid-solid growth, enabling precise control of crystal phases and the creation of CPQDs with monolayer precision. Nanowires are epitaxially grown on custom-made silicon microsubstrates using chemical vapor deposition within an in situ TEM. Real-time imaging reveals that the electric field instantaneously switches the crystal phase between zinc blende and wurtzite, creating atomically sharp interfaces. Numerical simulations are developed to investigate the impact of the electric field on the catalyst droplet geometry, which largely governs the crystal phase. This constitutes key progress toward unlocking the potential of CPQDs.