Possible theoretical models for carrier diffusion coefficient of one-dimensional Si wire devices

We use the semi-microscopic theory to elucidate the effective diffusion coefficient of carriers in one-dimensional Si wire devices. In the theoretical model, it is assumed that the primary spectrum of the diffusion process of majority and minority carriers rules the diffusion process; a statistical assessment of the diffusion coefficient is performed using quantum-mechanical analysis. Here the model assumes that the thermalization of carrier transport is ruled by the specific characteristic length. The theory reveals that the diffusion coefficient drastically decreases as the wire width enters the sub-10-nm range. Although it is suggested that the behavior of the diffusion coefficient of such Si wires is related to phonon scattering events in narrow wires, it is not so clear whether it is the dominant mechanism ruling the diffusion coefficient of Si wires. A quantitative prediction of carrier mobility in Si wires is also made on the basis of Einstein's relation, and the model's validity is examined. (C) 2015 The Japan Society of Applied Physics