PhD ceremony Mr. G. Eising: Crystallization phenomena in germanium antimony phase-change films

PhD ceremony: Mr. G. Eising

Dissertation: Crystallization phenomena in germanium antimony phase-change films

Promotor(s): prof. B.J. Kooi

Faculty: Mathematics and Natural Sciences

Phase-change materials are currently widely used in rewritable optical media, where the differences in optical properties between the meta-stable amorphous phase and the stable crystalline phase are used to store binary information. Apart from the optical differences, there is also a strong difference in electrical resistance between the two phases, and this is being used to create an electrical memory, which has proven to be an interesting candidate for the next-generation memories.

In this thesis the crystal growth properties of germanium antimony alloys are studied. Using a high-speed optical camera we were able to directly observe the crystal growth. By changing the alloy by only a few atom percentages we observed a strong change in growth rates and activation energies during isothermal measurements. By further increasing the temperature we show that the often used Arrhenius dependence is not valid at higher temperatures.

By inducing external stresses in the phase-change films we are able to increase and decrease the crystal growth rate. Additionally, we are able to create one dimensional growth by using anisotropic stresses. Differences in electrical properties were studied and a Schottky barrier was found at the amorphous-crystalline interface with associated potential difference.

Next to the experimental studies we computationally studied crystal nucleation by simulation the growth and decay of critical clusters.