In Situ Observation of Higher Order Polytypes in Au-Seeded GaAs Nanowires

Abstract Crystal phase selection in III−V semiconductor nanowires is one of the key aspects of these structures that has enabled their successful use in devices. In addition to the commonly known polytypes zinc blende (ZB) and wurtzite (WZ) there exist rare, higher order polytypes such as 4H, 6H, and 8H. These rare polytypes may present unique material properties provided they can be controllably grown. To enable robust growth of the higher order polytypes, we first need to understand their formation on a fundamental level in addition to realizing how they fit within the currently known crystal phase trends. Here, we present an in situ study of polytypism in GaAs nanowires, first mapping crystal phase as a function of V/III ratio. We can observe the same crystal phase trends as in previous growth studies using ex situ systems and modeling, namely, that WZ crystal phase exists in a growth window between low and high V/III ratio ZB crystal phase. Next, we demonstrate that transient growth of long-range polytypes including 4H, 6H, and 8H is possible for growth parameters between the high V/III ratio ZB and WZ crystal structures. Furthermore, we provide a qualitative interpretation of how long-range polytypes can be incorporated into the existing models by proposing that here supersaturation exhibits deterministic trends. Lastly, we demonstrate how our in situ results translate to ex situ systems.