Geometric Effects On Carrier Collection In Core-Shell Nanowire P-N Junctions

We report electron-beam-induced current (EBIC) microscopy carried out on free-standing GaAs nanowire core-shell, p-n tunnel junctions. The carrier kinetics in both the n-type core and the p-type shell were determined by analyzing radial EBIC profiles as a function of beam energy. These profiles are highly sensitive to geometric effects such as facet width, shell and core thicknesses, and depletion widths. Combined with Monte Carlo simulations, they permitted measurement of the minority carrier diffusion lengths in the core and the shell, as well as the depletion widths as a function of radial direction. The relatively short minority carrier diffusion length in the core (50 nm), can be attributed to bulk point defects originating from low-temperature core growth (400 C-circle), or to interfacial recombination at traps at the p-n junction.