Controlled Formation of Radial Core–Shell Si/Metal Silicide Crystalline Heterostructures

Abstract

The highly controlled formation of "radial" silicon/NiSi core-shell nanowire heterostructures has been demonstrated for the first time. Here, we investigated the "radial" diffusion of nickel atoms into crystalline nanoscale silicon pillar 11 cores, followed by nickel silicide phase formation and the creation of a well-defined shell structure. The described approach is based on a two-step thermal process, which involves metal diffusion at low temperatures in the range of 200-400 °C, followed by a thermal curing step at a higher temperature of 400 °C. In-depth crystallographic analysis was performed by nanosectioning the resulting silicide-shelled silicon nanopillar heterostructures, giving us the ability to study in detail the newly formed silicide shells. Remarkably, it was observed that the resulting silicide shell thickness has a self-limiting behavior, and can be tightly controlled by the modulation of the initial diffusion-step temperature. In addition, electrical measurements of the core-shell structures revealed that the resulting shells can serve as an embedded conductive layer in future optoelectronic applications. This research provides a broad insight into the Ni silicide "radial" diffusion process at the nanoscale regime, and offers a simple approach to form thickness-controlled metal silicide shells in the range of 5-100 nm around semiconductor nanowire core structures, regardless the diameter of the nanowire cores. These high quality Si/NiSi core-shell nanowire structures will be applied in the near future as building blocks for the creation of utrathin highly conductive optically transparent top electrodes, over vertical nanopillars-based solar cell devices, which may subsequently lead to significant performance improvements of these devices in terms of charge collection and reduced recombination.

Revealing Seed‐Mediated Structural Evolution of Copper‐Silicide Nanostructures: Generating Structured Current Collectors for Rechargeable Batteries

“…[2][3][4]9,13,32,[49][50][51][52][53][54][55][56][57] A large range of transition metal silicide NWs with different crystal phases has been synthesized using these techniques. [23,[58][59][60][61][62][63][64][65][66][67][68][69] However, the controlled synthesis and reproducibility of metal silicide NWs is challenging due to the complex metal-Si phase diagrams, with the possibility of numerous metal silicide stoichiometries. [1,2,9,13,50,70,71] Furthermore, the mechanisms behind anisotropic metal silicide NWs growth remain unclear.…”

Controlled Silicidation of Silicon Nanowires Using Flash Lamp Annealing

“…They demonstrated Schottky barrier-based transistors using this process. A third variant was first reported by Kosloff et al, 38 where diffusion of Ni into Si nanopillars at 200−400 °C was used to form a Si−NiSi core− shell nanowire.…”