Controlled nonuniformity in macroporous silicon pore growth

Photoelectrochemical etching of uniform prestructured silicon wafers in hydrofluoric acid containing solutions yields periodic structures that can be applied to two- and three-dimensional photonic crystals or microfluidics. Here we demonstrate experimentally macroporous silicon etching initiated by a nonuniform predefined lattice. For conveniently chosen parameters we observe a stable growth of pores whose geometrical appearance depends strongly on the spatially different nucleation conditions. Moreover, we show preliminary results on three-dimensionally shaped pores. This material can be used to realize hybrid photonic crystal structures and incorporate waveguides in three-dimensional photonic crystals

A Novel Method to Fabricate Silicon Nanowire p–n Junctions by a Combination of Ion Implantation and in-situ Doping

We demonstrate a novel method to fabricate an axial p–n junction inside <111> oriented short vertical silicon nanowires grown by molecular beam epitaxy by combining ion implantation with in-situ doping. The lower halves of the nanowires were doped in-situ with boron (concentration ~1018cm−3), while the upper halves were doubly implanted with phosphorus to yield a uniform concentration of 2 × 1019 cm−3. Electrical measurements of individually contacted nanowires showed excellent diode characteristics and ideality factors close to 2. We think that this value of ideality factors arises out of a high rate of carrier recombination through surface states in the native oxide covering the nanowires

Tree-like alumina nanopores generated in a non-steady-state anodization{

Novel tree-like alumina nanopores were reproducibly obtained in non-steady-state anodization conditions by exponential decrease of anodization potential. The mechanism of pore formation was thought to be due to a combination of electrical treeing and mechanic stress in the growth process. Furthermore, some interesting properties from gold nanotrees were observed showing that the tree-like nanopores will be new templates towards fabrication of nanotrees from a variety of materials possibly exhibiting new shape-dependent properties. Nanoporous alumina formed by electrochemical anodization of aluminium in acid electrolytes has been extensively studied for more than 50 years. 1 Wood&apos;s model 2 and further modified models 3,4 can give satisfactory interpretations of many experimental phenomena, such as monodispersity of pore size distribution, linear dependence of pore diameter and inter-pore distance on the applied anodization potential. However, these models cannot easily explain well some recent findings, such as selfordered pore growth in two-step anodization, 5,6 self-ordering under high-field anodization 7,8 and at burning potential, 9 guided pore growth by imprint lithography, 10,11 etc. In order to understand the self-ordering pore growth mechanism, repulsive interactions between the pores 12 and high electric field theory 7-9 have been proposed. In contrast to the extensive research efforts on steady-state anodization, non-steady-state anodization has been given little attention. Here, it was found that unexpected tree-like alumina nanopores were generated in non-steady-state anodization when the anodization potential was decreased exponentially in a stepwise way. The development of pores is more like that of tree or root in nature, which cannot be simply explained by Wood&apos;s models. 17,18 Scheme 1 illustrates the fabrication process of tree-like alumina nanopores. Firstly, ordered nanopore arrays were fabricated via well-established two-step anodization in oxalic acid at 40 V (see details in ESI{). The nanopores have a depth of y2 mm, and a diameter of y35 nm. Then, the anodization potential was decreased exponentially from 40 V to 5 V. The change of the applied anodization potential as a function of time is shown i

Wafer bonding: applications and technology

During the past decade direct wafer bonding has developed into a mature materials integration technology. This book presents state-of-the-art reviews of the most important applications of wafer bonding written by experts from industry and academia. The topics include bonding-based fabrication methods of silicon-on-insulator, photonic crystals, VCSELs, SiGe-based FETs, MEMS together with hybrid integration and laser lift-off. The non-specialist will learn about the basics of wafer bonding and its various application areas, while the researcher in the field will find up-to-date information about this fast-moving area, including relevant patent information