Studies of the self-assembled growth mechanism on nanocrystalline silicon nanodots

Abstract

Nanocrystalline silicon (nc-Si) nanodots have been grown on corning glass (7059) substrate using a self-assembly VHF-PECVD method under the following experimental conditions: Fixed deposition temperatures of 300/400 °C, deposition times 30/60 s, plasma power of 10 W, silane gas flow rate of 10 sccm, as well as deposition pressure of 10-2 torr. It is predicted that the onset of nucleation began immediately after the deposition and start to appear clearly after 20-60 s during which growth mechanisms occur. Essentially, the nanodots were formed onto the substrate in dome-like shapes by virtue of equilibrium surface energies, yLS, yLN and yNS. The associated liquid/solid nucleation mechanism was then simulated and related parameters were obtained: Free energy change per unit volume ?Gv ~-104 Jmol-1; Surface energies per unit area, ?LN = 1.44 Jm-2, ?NS = 19 - 60 Jm-2 and ?LS = 0.74 Jm-2; Critical energies ?G* ~10-15 J; Critical radii r* = 16 - 48 nm. These results were experimentally verified, in particular for selected critical radius r* less than 50 nm. Other measurements were also carried out: PL analysis gave bandgap energies ~ 1.8-2.4 eV, whilst Raman spectra revealed the coexistence of nc-Si and amorphous Si. It is strongly suggested that, the nc-Si nanodot grown on glass substrate fulfills the Volmer-Weber growth mode with a minor modification.