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Diffusion of silicon in crystalline germanium

2006; IOP Publishing; Volume: 21; Issue: 6 Linguagem: Inglês

10.1088/0268-1242/21/6/008

1361-6641

Hughes H. Silvestri, H. Bracht, J. Lundsgaard Hansen, A. Nylandsted Larsen, E. E. Häller,

Semiconductor materials and interfaces

We report the determination of the diffusion coefficient of Si in crystalline Ge over the temperature range of 550 to 900 °C. A molecular beam epitaxy (MBE) grown buried Si layer in an epitaxial Ge layer on a crystalline Ge substrate was used as the source for the diffusion experiments. For samples annealed at temperatures above 700 °C, a 50 nm thick SiO2 cap layer was deposited to prevent decomposition of the Ge surface. The temperature dependence of the diffusion coefficient can be described by a single activation energy (3.32 ± 0.03 eV) and pre-factor (42+21−14 cm2 s−1) over the entire temperature range studied. Our diffusivity data extend former measurements by two orders of magnitude at the low temperature end. The diffusion of the isovalent Si in Ge is slower than Ge self-diffusion over the full temperature range and reveals an activation enthalpy that is higher than that of self-diffusion. This points to a reduced interaction potential between the Si atom and the native defect mediating the diffusion process. For Si, which is smaller in size than the Ge self-atom, a reduced interaction is expected for a Si–vacancy (Si–VGe) pair. Therefore we conclude that Si diffuses in Ge via the vacancy mechanism.