Early-Stage Nucleation Behavior of GaAs Nanowires on Si Substrate based on In-Situ TEM

To take advantage of the unique physical properties of nanowires (NWs), it is crucial to accurately control their geometry, crystal structure, and doping level. This goal will ultimately be achieved by a deeper understanding of the growth mechanisms.<br/><br/>Meanwhile, the initial stages of the growth process are the least understood and have been investigated almost exclusively by ex-situ techniques. Here, we present real-time observations of the nucleation and growth of self-catalyzed GaAs nanowires using a transmission electron microscope (TEM) equipped with molecular-beam-epitaxy (MBE) sources. Custom-made floating substrates, in the form of electron-transparent &lt;111&gt;-oriented Si membranes, were fabricated using MEMS (Micro-electromechanical Systems) technology. A combination of finite-element simulations and Raman spectroscopy was used to accurately calibrate the sample temperature and optimize its design. The results were in good agreement and further verified by the dimension and distribution of pre-deposited Ga droplets.<br/><br/>Nanowires were grown directly on the membrane inside the microscope via a vapor-liquid-solid mechanism as a practical MBE configuration and the process was monitored <i>in situ</i> and in real-time with high spatial and temporal resolution. On the base of our direct observations, the main steps of this dynamic process, from Ga droplet deposition to crystal nucleation at the interface as well as the vertical growth of nanowires will be discussed.