In-situ Neutron Reflectometry to Determine Ge Self-Diffusivities and Activation Energy of Diffusion in Amorphous Ge_0.8Si_0.2

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.

Self-Diffusion of Ge in Amorphous GexSi1–x Films Studied In Situ by Neutron Reflectometry

“…x = 1 2.11 ± 0.12 −5.23 ± 1.0 x = 0.80 2.07 ± 0.10 −6.20 ± 1.0 x = 0.43 2.85 ± 0.12 −2.15 ± 0.8 x = 0.13 3.44 ± 0.10 0.57 ± 0.4 x = 0 4.40 ± 0.30 4.17 The data of Si self-diffusion in amorphous silicon produced by sputter deposition 50 is marked with a blue filled square and that produced by Si-ion implantation 43 with an open triangle. The activation enthalpy of Ge self-diffusion in amorphous germanium 44,51,57 and that in amorphous Ge 0.8 Si 0.2 , 58 Ge 0.43 Si 0.57 and Ge 0.13 Si 0.87 are marked with red-filled circles. (b) Activation enthalpy (ΔH) of self-diffusion as a function of x in crystalline Ge x Si 1−x .…”

“…The substrates were cleaned with isopropanol. The deposition rate was determined by XRR measurements as described in ref . The as-deposited multilayers have a total thickness of around 280 nm.…”

“…Neutron reflectometry (NR) ,− is such a nondestructive method. During the last years our group used and developed the method of NR in order to monitor atomic diffusion in situ or in-operando and in real time. ,− ,− …”