FIB Patterned Templates for Guided Nanostructure Formation

FIB PATTERNED TEMPLATES FOR GUIDED NANOSTRUCTURE FORMATION\ud Hao Wang, PhD\ud University of Pittsburgh, 2013\ud \ud There are many factors that limit significant advances in device technology, including the ability to arrange materials at shrinking dimensions and the ability to successfully integrate new materials having better properties with silicon. Methods for self-assembly of quantum dots are greatly desired for new devices which have smaller sizes, lower energy consumption, higher performance, and new functionality. In order to create such new devices, a patterning method must be used that can arrange quantum dots at the appropriate length scales. A focused ion beam (FIB) is one method of laterally arranging nanosized islands of dissimilar materials on silicon by creating template patterns directly on the Si substrate with nanoscale resolution. With the intention of promoting self-assembly of nanostructures, surface topography features and chemical/compositional variations are used in the near surface region of the templates. Two changes are taking place simultaneously during the milling process: surface topography is created as material being removed while implanted Ga is added. The implanted Ga can form clusters or nanocrystals when heating.1,2 Both processes are of potential interest for lateral positioning of nanostructures. \ud One possible concern for device applications is the effect of the implanted Ga which is a result of the milling process. Implantation can result in damage to the lattice, unwanted doping of the substrate, and/or nucleation of Ga nanocrystals from the implanted material. On the other hand, it may also be desirable in some scenarios to take advantage of the implanted material and nucleate nanostructures directly from it. For example, Ga surface islands could result upon annealing with the potential to be converted to Ga-based compounds, such as GaN, on Si through chemical reactions. GaN is a direct band gap material and of interest for electrically pumped ultraviolet-blue LEDs(light-emitting diodes), lasers, and potentially for single photon sources.3–6 \ud For a lattice mismatched system such as SiGe/Si, the topography created by the FIB can lead to the formation of strain-relieving islands at the preferential sites. For the case of SiGe/Si, the physical evaporation of Si and Ge under UHV(ultra-high vacuum) conditions, that deposition of epitaxial strained SiGe on top of a FIB patterned Si substrate can lead to preferential island formation at FIB patterned pit edges under appropriate growth conditions.7 \u