Role of self-interstitials on B diffusion in Ge

B diffusion in crystalline Ge is investigated under equilibrium and non-equilibrium conditions in a large temperature range (200-800 degrees C), in order to discriminate the role of self-interstitials (Is) and the energy barriers involved in the microscopic mechanism of B migration. To this aim, we copiously furnished Is by 200 or 300 key H+ irradiation, and performed a direct comparison with B diffusion in thermal conditions at the same temperature (T). The diffused profiles of B were simulated assuming the kick-out model, and the extracted parameters (migration length, lambda, and formation rate of mobile B, g) indicated that the B diffusion is always mediated by Is showing different features at low and high T regimes. For T lower than 600 degrees C the thermal generation of Is is negligible and the only barrier to g (measured to be similar to 0.1 eV) is due to the Is migration and B mobile formation. At T higher than 600 degrees C, the thermal generation of Is starts to overcome the Is supply from the irradiation, and the activation energy of g increases to 3.0-3.5 eV. The migration length in the low-T regime has the largest value (similar to 20 nm), while it decreases down to 1-2 nm by increasing T, showing a negative activation energy of similar to-0.64 eV, compatible with a dissociation process which stops the diffusion event. In this regard, we observed that the mobile B migration length depends only on T, regardless of the point defects concentration. These results and the energy barriers measurements contribute to a further comprehension of the B diffusion and point defects in crystalline Ge. (C) 2011 Elsevier B.V. All rights reserved.