Influence of Plasma Stimulation on Si Nanowire Nucleation and Orientation Dependence

Abstract

One-dimensional nanoscale materials play a key role in nanotechnology, as well as provide model systems to explore new properties. Semiconductor nanowires grown by the vapor-liquid-solid (VLS) process are a natural choice to explore electronic and optoelectronic properties of 1D systems because of their high crystalline quality and because their diameters and length can be controlled during synthesis in a predictable manner. In VLS growth gaseous reactants drive nanowire growth from liquid metal catalyst nanodots, the size of which defines the diameter of the nanowires.[ [4] However despite numerous studies there is still only limited understanding of the basic mechanisms that control nanowire nucleation and the resulting orientation dependence. [5][6][7][8][9] In the present work we introduce a plasma during silane-hydrogen VLS nanowire growth on Si (100) The ability to carry out growth at low temperatures is important for device integration and is essential for maintaining the integrity of nanoscale structures. For thermally activated, low-pressure chemical vapor deposition (LPCVD) with silane-hydrogen gas mixtures, VLS growth temperatures of 450°C or higher are typically required for reasonably rapid growth rates and for high quality single crystal nanowires. However, the addition of low power rf (13.56 MHz) plasma increases the concentration of more reactive Si containing gas species and the incorporation of Si into the Au liquid eutectic catalyst. This effect in turn promotes higher growth rates. One advantage of growing nanowires at low temperatures is that the mobility and size coarsening of the Au seeds is minimized, promoting the growth of smaller diameter nanowires.Up to now there have been only a few studies reported for plasma enhanced growth of nanowires. Hofmann et al.[10] reported Au catalyzed Si nanowire growth on amorphous SiO 2 substrates below 400°C by LPCVD with silane under rf plasma stimulation and found significant enhancements in the growth rate. Sharma and Sunkara [11] demonstrated Si nanowire growth from molten Ga in the presence of microwave plasmas of silane and hydrogen gases. We are interested in quantitatively comparing nanowire nucleation, growth rates, and orientations under thermal and plasma stimulated conditions for seeded growth from crystalline substrates. In our work Si nanowires were grown in an LPCVD reactor on Au seeded Si (100) surfaces from hydrogen-diluted silane gases under thermal conditions, both with and without a 2.5W rf plasma. Growth temperatures were varied from 300 to 430°C. Generally, the overall nanowire density is significantly greater under plasma compared to thermal growth conditions.

Plasma‐Assisted Approaches in Inorganic Nanostructure Fabrication

“…[57,87,89,142] The nucleation, growth, and crystallization behavior of the nanostructures can be tuned due to the new chemistry equilibrium induced by the excited species at the plasma/solid interface. [47,55,92,106,117,125] Moreover, radicals and ions exhibit a synergic effect, which has been verified in plasma etching processes. [226,227] The particle formation in plasmas usually occurs in cases of high precursor density and higher power density, [96][97][98]102] which can be either enhanced or weakened by controlling the plasma conditions according to the purpose.…”

“…Excitation by radio-frequency plasma during the growth resulted in a notable increase in [110] oriented nanowires with much narrower diameter. [125] The tuning of orientation was attributed to the higher Si chemical Although not well understood, the mechanism of electric-field guided growth in inorganic crystalline one-dimensional nanostructures is different from that in the CNTs. [47,[52][53][54] In CNT growth, the electric-field force is the driving force to align the CNTs.…”

“…The plasma, however, can amplify certain crystal-growth features indirectly, such as changing the precursor spatial distribution or the chemical potential. [55,125] Experimental evidences and theoretical insights into this issue are still insufficient and need further investigation.…”

The effect of microscopic texture on the direct plasma surface passivation of Si solar cells

“…[18][19][20][21][22] It should also be noted that hydrogen can have a similar role in growth of metal oxide nanostructures. [23][24][25][26][27][28][29][30][31][32] The H þ ions are randomly distributed over the simulation plane with the length and width of 44 lm; this plane is located at the sheath edge and is parallel to the substrate. The initial velocities of the ions are equal to the Bohm velocity.…”

Semiconductor Nanowires

“…38, 69 The decomposition chemistry occurring away from the seed metal in the reaction media can also be tuned by the choice of reactant and reaction conditions. Ultimately, the quality of the nanowires -the defect density, the diameter variation, the amount of non-nanowire reaction by-products -relate to the reaction chemistry.…”