Templated self-organization of SiGe quantum structures for nanoelectronics

A central challenge for modern device technology aiming towards nanoelectronics, spintronics and quantum computation is to implement exact control in the positioning of nanostructures like quantum dots. Templated self-organization, i.e. combining the well developed top-down approaches to fabricate nanostructures in the microelectronics with bottom-up techniques of self-assembly offers a variety of new paths for the implementation of nanostructures into modern device technology. In this paper two routes are discussed, the ordering of Ge quantum dots on prepatterned Si substrates and the self-scrolling process of Si/SiGe as well as Si/SiGe/Cr hybrid structures into 3-dimensional nano-objects. Prepatterning of Si substrates is achieved by extreme ultra-violet interference lithography (EUV-IL) using diffractive optics exposing areas of typically 0.7 × 0.7 mm2 in a single exposure with perfect periodicity. 2-Dimensional hole arrays have been fabricated using EUV-IL and reactive ion etching. Subsequently, molecular beam epitaxy was employed to grow Si/Ge 2-dimensional quantum dot arrays on the prepatterned substrates. Adjusting the exposure and MBE growth conditions, the perfection of ordering and the density of ordered dots is controlled. Moreover, the ordering of quantum dot molecules, comprising 4 quantum dots per lattice point, has been achieved. Scrolled nano-objects were fabricated from Si/SiGe as well as Si/SiGe/Cr hybrid layered structures. Patterned by standard lithographic techniques into mesa structures, underetching leads to a scrolling of the layer stacks into nanotubes, nanospirals and other 3-d objects due to strain relaxation. Entering the nanometer regime anomalous scrolling is observed. Possible applications for quantum dots and scrolled nanotubes for nanoelectronic devices are discussed.