Oscillations of As Concentration and Electron-to-Hole Ratio in Si-Doped GaAs Nanowires.

III-V nanowires grown by the vapor-liquid-solid method often show self-regulated oscillations of group V concentration in a catalyst droplet over the monolayer growth cycle. We investigate theoretically how this effect influences the electron-to-hole ratio in Si-doped GaAs nanowires. Several factors influencing the As depletion in the vapor-liquid-solid nanowire growth are considered, including the time-scale separation between the steps of island growth and refill, the "stopping effect" at very low As concentrations, and the maximum As concentration at nucleation and desorption. It is shown that the As depletion effect is stronger for slower nanowire elongation rates and faster for island growth relative to refill. Larger concentration oscillations suppress the electron-to-hole ratio and substantially enhance the tendency for the p-type Si doping of GaAs nanowires, which is a typical picture in molecular beam epitaxy. The oscillations become weaker and may finally disappear in vapor deposition techniques such as hydride vapor phase epitaxy, where the n-type Si doping of GaAs nanowires is more easily achievable.