Facile fabrication of ordered Si1-xGex nanostructures via hybrid process of selective epitaxial growth (SEG) and self-assembled nanotemplates

Abstract

In this study, a facile fabrication method of the ordered Si1-xGex nanodots (NDs) and nanowires (NWs) was successfully developed via hybrid process of selective epitaxial growth (SEG) of Si1-xGex and self-assembled nanotemplates, i.e., anodic aluminum oxide (AAO) and diblock copolymer (DBC) of polystyrene-b-polymethylmethacrylate (PS-b-PMMA). Si1-xGex films were selectively grown on the Si windows against the oxide area at a growth temperature of 550 degrees C by repeating the unit cycle consisting of two consecutive steps; Si1-xGex deposition step using Si2H6 and GeH4 and Cl-2 exposure step for removing the nuclei or deposits formed on the oxide area during the preceding Si1-xGex deposition step. The chemical composition of the Si1-xGex films was readily controlled by adjusting the flow rate of GeH4 from 20 sccm to 45 sccm while that of Si2H6 gas was fixed at 10 sccm, giving rise to the variation of Ge composition in Si1-xGex from 22.2% to 34.0%.

In order to fabricate well-ordered Si1-xGex nanostructures, Si windows with hexagonal arrangement were fabricated using AAO and PS-b-PMMA. AAO was prepared through multi-step anodization of the Al films of Al/Si(001) substrate under suitable anodizing conditions. Subsequently, ordered Si windows were fabricated by removing the barrier layer at the bottom of the AAO membrane by reactive ion etching (RIE). In case of PS-b-PMMA, SiO2 templates with ordered Si windows were fabricated through replication of nano-cylindrical pattern of PS-b-PMMA to the 20-nm thick SiO2 layers of SiO2/Si. By utilizing the ordered Si windows obtained from both AAO and PS-b-PMMA, Si1-xGex was selectively grown on Si windows against the oxide area, viz., aluminum oxide in AAO and SiO2 templates. Hexagonally ordered NDs and freestanding NWs were facilely fabricated on the Si substrates after removing the AAO and SiO2 templates. (C) 2012 Elsevier B.V. All rights reserved.