Hierarchical-Oriented Si/ZnO Heterostructured Nanowires

In this work, self-catalytic growth of zinc oxide (ZnO) nanostructures on silicon nanowires (Si NWs) was studied using a vapor transport and condensation (VTC) method. ZnO seeded Si NWs were used as a base for the growth of ZnO nanostructure branches. We investigated the changes in morphologies of the ZnO nanostructures by varying the average size of the ZnO seeds and ZnO evaporation time. Our observations showed that the larger ZnO seeds are energetically more stable in promoting growth of ZnO nanorods (NRs) along the [0001] direction (c-axis). Increase in ZnO evaporation time lengthens the ZnO NRs, however, results in non-uniform diameter along the NRs due to irregular supply and precipitation of ZnO vapors on the non-polar surfaces of the NRs. The mechanisms of the seed size-dependent growth and time-dependent growth of ZnO nanostructures on Si NWs base were addressed. The hierarchical oriented Si/ZnO heterostructure NWs revealed interesting optical properties, among which, an enhancement in near band edge emission and suppression in optical reflection of the Si NWs.