Experimental investigations of boron diffusion mechanisms in crystalline and amorphous silicon

Boron, as the main p-type dopant in Si, has been extensively investigated both experimentally and theoretically in order to understand its diffusion mechanisms for modelling and optimization of advanced devices. Crystalline Si matrix was mostly studied, but quite recently increased interest emerged on the behaviour of B in amorphous Si. In this work we present our recent progress in understanding these fundamental processes. Extensive investigation about the room temperature diffusion of B induced by the analyzing beam during secondary ion mass spectrometry, allowed to give information about diffusion mechanism of B both in crystalline and in amorphous phase. Moreover this put the basis for accurate measurements that allowed to investigate the key parameters describing the B diffusion in different equilibrium conditions, i.e. in wide ranges of temperature and doping level. On this basis, a comprehensive, experimentally based, atomistic model for B diffusion has been assessed, advancing and clarifying in a coherent picture the wide existing literature, including the interactions among B and self-interstitial in different charge states. Also the amorphous phase shows a complex B diffusion mechanism, far from being Fick-like. By means of simulation modelling of extensive diffusion data, produced in a wide range of temperatures, times and B concentrations, we have demonstrated that B promotes the formation of dangling bonds and it interacts with them in order to diffuse. Peculiar physical features, such as diffusion shape and transient diffusion, are correctly described by the model.