Crystal phase engineering in self-catalyzed GaAs and GaAs/GaAsSb nanowires grown on Si(111)

• Self-catalyzed GaAs and GaAs/GaAsSb NWs are grown on Si(111).
• GaAs crystal phase engineering is demonstrated by tuning Ga droplet contact angle.
• Fraction of TPL in contact with NW side wall dictates ZB/WZ nucleation probability.
• Contact angle is controlled by GaAsSb insert, flux interruption and V/III ratio.
• Challenges for obtaining abrupt GaAs crystal phase heterointerface are discussed.

Accomplishing control of the crystal phases in III–V semiconductor nanowires (NWs) is important for applications in future advanced nano-devices. In this work, we report on the growth of both zinc blende (ZB) and wurtzite (WZ) GaAs in self-catalyzed GaAs and GaAs/GaAsSb axial heterostructured NWs on Si(111) substrates by the vapor–liquid–solid technique using molecular beam epitaxy. The self-catalyzed GaAs NWs usually adopt the ZB phase. However, by growing GaAs NWs with short GaAsSb axial inserts, the crystal phase of GaAs can be changed from ZB below the GaAsSb insert, to WZ above. This crystal phase change in GaAs can be explained in terms of a change in the contact angle of the Ga droplet which changes the fraction of the triple-phase-line in contact with the edge of the NW top facet and therefore affects the probability of nucleation for ZB and WZ phases. In addition, by growing ZB GaAs after the insert using a flux interruption, we demonstrate the growth of all combinations of crystal phases of the GaAs segments on both sides of the GaAsSb insert. This understanding has also enabled us to achieve the growth of WZ phase in GaAs NWs as well as a ZB–WZ–ZB GaAs NW heterostructure, by changing the Ga droplet contact angle, without growing a GaAsSb insert. The contact angle was controlled by introducing different flux interruptions and tuning the V/III flux ratio.