Formation Of Si Nanostructures Research Articles

Effect of the Graded Silicon Content in SRN/SRO Multilayer Structures on the Si Nanocrystals and Si Nanopyramids Formation and Their Photoluminescence Response.

Two multilayer (ML) structures, composed of five layers of silicon-rich oxide (SRO) with different Si contents and a sixth layer of silicon-rich nitride (SRN), were deposited by low pressure chemical vapor deposition. These SRN/SRO MLs were thermally annealed at 1100 °C for 180 min in ambient N2 to induce the formation of Si nanostructures. For the first ML structure (MLA), the excess Si in each SRO layer was about 10.7 ± 0.6, 9.1 ± 0.4, 8.0 ± 0.2, 9.1 ± 0.3 and 9.7 ± 0.4 at.%, respectively. For the second ML structure (MLB), the excess Si was about 8.3 ± 0.2, 10.8 ± 0.4, 13.6 ± 1.2, 9.8 ± 0.4 and 8.7 ± 0.1 at.%, respectively. Si nanopyramids (Si-NPs) were formed in the SRO/Si substrate interface when the SRO layer with the highest excess silicon (10.7 at.%) was deposited next to the MLA substrate. The height, base and density of the Si-NPs was about 2–8 nm, 8–26 nm and ~6 × 1011 cm−2, respectively. In addition, Si nanocrystals (Si-ncs) with a mean size of between 3.95 ± 0.20 nm and 2.86 ± 0.81 nm were observed for the subsequent SRO layers. Meanwhile, Si-NPs were not observed when the excess Si in the SRO film next to the Si-substrate decreased to 8.3 ± 0.2 at.% (MLB), indicating that there existed a specific amount of excess Si for their formation. Si-ncs with mean size of 2.87 ± 0.73 nm and 3.72 ± 1.03 nm were observed for MLB, depending on the amount of excess Si in the SRO film. An enhanced photoluminescence (PL) emission (eight-fold more) was observed in MLA as compared to MLB due to the presence of the Si-NPs. Therefore, the influence of graded silicon content in SRN/SRO multilayer structures on the formation of Si-NPs and Si-ncs, and their relation to the PL emission, was analyzed.

Recent Progress in the Understanding of Si-Nanostructures Formation in <i>a</i>-SiN<sub>x</sub>:H Thin Film for Si-Based Optoelectronic Devices

There has been a rapidly increasing interest in the synthesis and characterization of Si- nanostructures embedded in a dielectric matrix, as it can lead to energy-efficient and cost-effective Complementary Metal-Oxide-Semiconductor (CMOS)-compatible Si-based light sources for optoelectronic integration. In the present contribution, first an overview of the SiOx as a dielectric matrix and its limitations are discussed. We then review the literature on hydrogenated amorphous silicon nitride (a-SiNx:H) as a dielectric matrix for Si-nanostructures, which have been carried out using silane (SiH4) and ammonia (NH3) as the reactant gases. Our studies demonstrate that the least amount of hydrogen in the as-deposited (ASD) a-SiNx:H films not only allows in-situ formation of Si-nanostructures but also stabilizes silicon nitride (Si3N4) phase. The recent advances made in controlling the shape and size of Si-nanostructures embedded in a-SiNx:H matrix by swift heavy ion (SHI) irradiation are briefly discussed.

Influence of Mass Transport on Formation of Si-Nanostructures

Nanowire-like, condyloid-like and flakes of Si-nanostructures weresynthesized by thermal evaporation under different mass transportconditions by changing the ambient pressure. The structural analysisshows that a higher mass transport rate isnot favourite for the formation of fine single crystalline nanowireswhen the substrate placed closely to the thermal vapour source. Thehigher mass transport rate can induce a lower Si partial pressure nearthe source and hence results in a lower supersaturation near thesubstrate. Experimental results reveal that the formation ofSi-nanowires is not controlled by mass transport but by surfaceprocess. The driving force on the surface is the key factor for theformation of well-crystallized nanowires.

XPS study of ion‐beam‐assisted formation of Si nanostructures in thin SiO2 layers

AbstractThin thermally grown SiO2 layers have been enriched with Si up to ∼15 at.% by Si ion implantation at room temperature. X‐ray photoelectron spectroscopy (XPS) was used to monitor the composition changes caused in the layers by bombardment with 3 keV Ar ions at elevated temperatures. Argon ion irradiation of pure SiO2 does not lead to the formation of Si nanoprecipitates. That was the case also for room‐temperature Ar bombardment of Si‐rich layers. Their ‘hot’ irradiation with Ar ions was found to enhance considerably the formation of segregated Si nanophase inclusions. The process starts at ∼500°C and becomes strongly pronounced at 650°C. At this temperature ion‐beam‐induced crystallization of Si nanoprecipitates may be achieved. The results obtained are explained in the framework of the physical model, based on the irradiation‐enhanced diffusion of excess Si atoms. Copyright © 2002 John Wiley & Sons, Ltd.

High reactivity of silicon suboxide clusters

The recent silicon-oxide-assisted formation of Si nanostructures has been studied based on quantum-mechanical calculations of ${\mathrm{Si}}_{n}{\mathrm{O}}_{m}$ $(n,m=1--8)$ clusters. We found that (1) energetically the most favorable small silicon-oxide clusters have O atomic ratios at around 0.6, and (2) remarkably high reactivity at the Si atoms exists in silicon suboxide ${\mathrm{Si}}_{n}{\mathrm{O}}_{m}$ clusters with $2n>m.$ The results show that the formation of Si-Si bonds is preferred and thus facilitates the nucleation of Si nanostructures when silicon suboxide clusters come together or stack to a substrate.

Low temperature process for nano-structure formation with Si films

Effects of sample preparation conditions on the formation of Si nano-structures were investigated. The samples were formed by various deposition methods with various deposition conditions, and subsequent oxidation and/or annealing was carried out. It was found that the film structure as well as the morphology of the thermally treated samples is greatly affected by not only the substrate temperature and the deposition rate but the presence of O 2 during deposition. In particular, O 2 flow during deposition was observed to apparently enhance formation as well as growth of Si grains. It was stated that the enhancement of crystallization is a consequence of formation and subsequent evaporation of SiO. These results were accounted for by formation kinetics of Si nano-structures. Furthermore, it was suggested that an optimized process for Si nano-structure may be obtained through modifications of the kinetics involved by systematic variations of the deposition conditions. In addition, I–V characteristics observed from the multiple junctions showed tunneling behavior implying the feasibility of fabricating novel devices such as single electron transistors.

Formation of Si nano-structures by O2 flow during deposition

Formation of Si nano-structures by O2 flow during deposition