Direct Observations of Twin Formation Dynamics in Binary Semiconductors

With the increaseddemand for controlled deterministic growth ofIII-V semiconductors at the nanoscale, the impact and interestof understanding defect formation and crystal structure switchingbecomes increasingly important. Vapor-liquid-solid (VLS)growth of semiconductor nanocrystals is an important mechanism forcontrolling and studying the formation of individual crystal layersand stacking defects. Using in situ studies, combiningatomic resolution of transmission electron microscopy and controlledVLS crystal growth using metal organic chemical vapor deposition,we investigate the simplest achievable change in atomic layer stacking-singletwinned layers formed in GaAs. Using Au-assisted GaAs nanowires ofvarious diameters, we study the formation of individual layers withatomic resolution to reveal the growth difference in forming a twindefect. We determine that the formation of a twinned layer occurssignificantly more slowly than that of a normal crystal layer. Tounderstand this, we conduct thermodynamic modeling and determine thatthe propagation of a twin is limited by the energy cost of formingthe twin interface. Finally, we determine that the slower propagationof twinned layers increases the probability of additional layers nucleating,such that multiple layers grow simultaneously. This observation challengesthe current understanding that continuous uniform epitaxial growth,especially in the case of liquid-metal assisted nanowires, proceedsone single layer at a time and that its progression is limited bythe nucleation rate.

Automated summary

The research focuses on the formation of single crystal layers and twinned layers in GaAs, revealing that twinned layers form significantly slower with the propagation being limited by the energy cost. The slower propagation of twinned layers increases the probability of nucleating additional layers.