Kris's Research Notes

September 6, 2011

Nanowires, Part 2

Filed under: GaAs Simulations — Kris Reyes @ 1:05 pm

Recall in this previous post, we discussed our first steps toward simulating VLS nanowire growth. In those simulations, we observed that the ‘solid’ behaved like a liquid which wet the substrate. Here, we address this by adjusting the desorption rate so that the solid phase is in equilibrium with the vapor phase.

Here is a simulation when the desorption rate is so adjusted:

This was with \gamma_{AA} = 0.40, \gamma_{BB} = 0.35, \gamma_{GA} = 0.10, \mu_{A} = 0.34 and \lambda_D = 0.7 eV.

As previously observed, the parameter \lambda_D does not seem to play much of a role in these simulations. Here are simulation results for the above parameter values, varying \lambda_D:

As before, we see different behavior depending on the relative strengths of the different energies. For example, here is a result where the nanowire grows on the substrate rather than perpendicular to it:

There are regimes in which nanowires fail to form entirely. For example, when \gamma_{BB} = \gamma_{AB}, the B material completely wets the surface:

We also see nanowires with a B-material core:

Perhaps most interestingly, we get bizarre structures that occur when the B-droplet splits during the formation of the nanowire. This tends to occur with smaller \lambda_D (so really quick diffusion through the B droplet) and (surprisingly counter-intuitive) with higher \gamma_{BB} bond strength. Here is one of the stranger results where we vary \lambda_D:

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