Self-Diffusion in Amorphous Silicon

The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on $^{29}\mathrm{Si}/^{\text{nat}}\mathrm{Si}$ heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and $700\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with an activation energy of $(4.4\ifmmode\pm\else\textpm\fi{}0.3)\text{ }\text{ }\mathrm{eV}$. In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about $700\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, which can be interpreted as the consequence of a high diffusion entropy.