Simulation of growth of silicon nanowhiskers with Ge-Si heterojunctions

The process of formation of Si-Ge heterostructures based on nanowhiskers (NWs) grown according to the vapor-liquid-solid mechanism is studied using the Monte Carlo simulation. It is found that, during growth of axial heterojunctions (HJs), it is impossible to obtain an atomically flat Si-Ge HJ, which is related to a gradual change in the catalyst-drop composition during the switch between fluxes. The dependence of the composition of the Ge (x) Si1 - x transition layer on the ratio of fluxes and on the Ge and Si deposition time is studied. It is found that the width of the axial Si-Ge HJs depends on the NW diameter. It depends linearly on the diameter under the adsorption-induced growth conditions and decreases with increasing diameter under the diffusion-induced growth conditions. This means that, as the NW thickness decreases, abrupt HJs in the Ge-Si system can be obtained only in the case of chemical-vapor-deposition growth in which the diffusion-induced growth component is insignificant.