Role of point defects on B diffusion in Ge

The key role of Ge in microelectronics is well established. Despite this, the behavior of dopants in Ge is not definitively clear. This paper aims at reviewing our experimental studies on B diffusion in Ge. In particular, B diffusion was investigated both in equilibrium and non-equilibrium conditions (i.e. during and after passing proton irradiation or during the dissolution of end of range defects produced by amorphization) in order to shed light on its microscopic mechanism as well as on the activation energies involved. The obtained results demonstrate that B diffusion in Ge is interstitials driven and that the found diffusion mechanism in Ge is still the same in equilibrium and non-equilibrium condition. Indeed, the mechanism that makes the B mobile species to return substitutional has an exponential behavior in which the diffusion length of the mobile species increases by decreasing the temperature, with an activation energy of −0.64 eV. On the basis of these results, B diffusion can be exploited to indirectly monitor the interstitial concentration in Ge. This is very important when a point defect engineering wants to be achieved. For instance, we demonstrates that O implantation and subsequent annealing leads to the formation of GeO₂ nanoclusters, that induces a high injection of interstitials, as monitored by the diffusion of B layers, with clear potentiality to control the diffusion of dopants that diffuse through a vacancy mediated mechanism.