A new method to fabricate size-selected compound semiconductor nanocrystals: Aerotaxy

A new method of fabrication is proposed to produce compound semiconductor nanocrystals with very narrow size distribution. It utilizes the formation of an aerosol of ultrafine group-III particles and their self-limited reaction with a group-V containing precursor at elevated temperatures. Since the new material grows in a self-organized fashion within the aerosol phase we call this process aerotaxy. GaAs nanocrystals, of approximate diameter 10 nm, have been produced by this method employing the reaction of Ga particles with arsine. The size of the final GaAs particle is self-limited by the size of the introduced size-selected Ga particle. This size can be tuned carefully. Transmission electron microscopy images exhibit good crystallinity of the particles. The kinetics of the transformation of Ga particles into GaAs nanocrystals depend on temperature and arsine flow. The starting temperature of this conversion was found to be as low as 200 degrees C, which may be the result of a very high V/III ratio. Studies on the variation of particle diameter with the conditions of formation have indicated activation energies for different process steps. Our approach opens the possibility to produce large quantities of size-selected nanocrystals of compound semiconductors.