Germanium Ge70/74Ge isotope heterostructures: An approach to self-diffusion studies

We demonstrate a technique to study self-diffusion in germanium, using isotope heterostructures (70Ge/74Ge). After interdiffusing the nominally undoped layers of Ge70 and Ge74 at temperatures between 543 and 690°C, the diffusion profiles are measured with secondary-ion-mass spectroscopy. The analysis of the experimental data allows an accurate determination of the self-diffusion enthalpy and the self-diffusion entropy. The isotope heterostructures are especially well suited for self-diffusion studies because the diffusion takes place at the interfaces inside the crystal. Thus, no surface effects or limited amounts of tracers complicate the measurements. We compare our results with those obtained with the standard techniques where the tracer self-diffusion coefficients are determined based on studying the redistribution of radioactive tracers, initially deposited on the specimen surface. Utilizing the stable isotopes in our experiment avoids complications due to decay of the radioactive tracers encountered in the traditional measurements.