In Situ Study of Axial GaSb/GaAs Nanowire Heterostructure Formation.

Combining multiple III-V materials into axial nanowire heterostructures has enabled the fabrication of custom nanowire-based devices useful for a wide range of applications. However, our ability to form axial heterostructures between arbitrary combinations of III-V compounds is impeded by a lack of information on the dynamics of the heterojunction formation process, often resulting in suboptimal heterostructure morphologies, particularly for materials including Sb. In this work, we utilize environmental transmission electron microscopy to examine the formation of GaSb/GaAs heterojunctions in Au-seeded nanowires in situ. We demonstrate that the growth parameter window for successful GaSb/GaAs heterostructure formation is very narrow and requires the growth of a ternary GaSb _x As_1-x segment. Furthermore, we show that as the nanowire changes the composition from GaSb to GaAs, the nanoparticle and nanowire morphologies are highly dynamic. At the end of the transition, we observe that the nanoparticle volume is halved and the nanowire diameter is reduced from ≈40 to ≈30 nm at the liquid-solid interface. Moreover, the nanowire growth rate increases by a factor of 7, when GaAs composition is reached, at our optimized growth conditions. Additionally, we are able to observe that the change in the crystal phase from GaSb zincblende (ZB) to GaAs wurtzite (WZ) happens via a mixed ZB-4H-WZ regime and is dependent not only on the nanowire composition but also on the vapor-phase composition in the growth chamber. These results offer unique insight into the formation dynamics of axial nanowire heterostructures, elucidating the interplay between all phases and growth species.