In-situ Neutron Reflectometry to Determine Ge Self-Diffusivities and Activation Energy of Diffusion in Amorphous Ge0.8Si0.2

Abstract

Amorphous Ge-Si solid solutions are an interesting class of materials from the fundamental as well as the technological point of view. Self-diffusion of the constituents is an important process because of the inherent metastability. While self-diffusion was already examined in crystalline GexSi1-x (0 < x <1) this is not the case for the amorphous counterparts. This work reports on Ge self-diffusivities obtained from insitu neutron reflectometry measurements during isothermal annealing of ion-beam sputter-deposited amorphous Ge0.8Si0.2 films. The diffusivities are modified peculiarly fast with annealing time by a maximum factor of two due to structural relaxation. The diffusivities in the relaxed state are lower (higher) than in amorphous germanium (silicon). They follow the Arrhenius law and show an activation energy of (2.06 ± 0.1) eV, which equals that of amorphous germanium, but differs from that of amorphous silicon. Thus, it is concluded that the diffusion mechanism of Ge in amorphous Ge0.8Si0.2 and Ge are similar, despite of the presence of dispersed 20 at.% of Si.