Modeling of the electron beam induced current signal in nanowires with an axial p-n junction.

A tridimensional mathematical model to calculate the electron beam induced current (EBIC) of an axial p-n nanowire junction is proposed. The effect of the electron beam and junction parameters on the distribution of charge carriers and on the collected EBIC current is reported. We demonstrate that the diffusion of charge carriers within the wire is strongly influenced by the electrical state of its lateral surface which is characterized by a parameter called surface recombination velocity ( v r ). When the surface recombination is weak (i.e. low v r value), the diffusion of charge carriers occurs in one dimension (1D) along the wire axis, and, in this case, the use of bulk EBIC models to extract the diffusion length ( L ) of charge carriers is justified. However, when the surface effects are strong (i.e. high v r values), the diffusion happens in three dimensions (3D). In this case, the EBIC profiles depend on v r value and two distinct cases can be defined. If the L is larger than the nanowire radius ( r a ), the EBIC profiles show a strong dependency with this parameter. This gives evidence that the recombination of generated carriers on the surface through v r is the dominant process. In this situation, a decrease of two orders of magnitude in the EBIC profiles computed with a high and a low v r value is observed in neutral regions of the junction. For the case of L smaller than r a the dependency of the EBIC profiles on the v r is weak, and the prevalent recombination mechanism is the bulk recombination process.