S.Y. Huang

Silicon on silicon: self-organized nanotip arrays formed in reactive Ar+H2 plasmas

The formation of arrays of vertically aligned nanotips on a moderately heated (up to 500 degrees C) Si surface exposed to reactive low-temperature radio frequency (RF) Ar+H(2) plasmas is studied. It is demonstrated that the nanotip surface density, aspect ratio and height dispersion strongly depend on the substrate temperature, discharge power, and gas composition. It is shown that nanotips with aspect ratios from 2.0 to 4.0 can only be produced at a higher RF power density (41.7 mW cm(-3)) and a hydrogen content of about 60%, and that larger aspect ratios can be achieved at substrate temperatures of about 300 degrees C. The use of higher (up to 500 degrees C) temperatures leads to a decrease of the aspect ratio but promotes the formation of more uniform arrays with the height dispersion decreasing to 1.5. At lower (approximately 20 mW cm(-3)) RF power density, only semispherical nanodots can be produced. Based on these experimental results, a nanotip formation scenario is proposed suggesting that sputtering, etching, hydrogen termination, and atom/radical re-deposition are the main concurrent mechanisms for the nanostructure formation. Numerical calculations of the ion flux distribution and hydrogen termination profiles can be used to predict the nanotip shapes and are in a good agreement with the experimental results. This approach can be applied to describe the kinetics of low-temperature formation of other nanoscale materials by plasma treatment.

From amorphous to microcrystalline: Phase transition in rapid synthesis of hydrogenated silicon thin film in low frequency inductively coupled plasmas

Hydrogenated silicon (Si:H) thin films were fabricated on glass substrates by low frequency inductively coupled plasma-assisted chemical vapor deposition using a silane precursor with low hydrogen dilution at room temperature. The crystallinity and microstructure properties of the Si:H thin films deposited at different inductive radio-frequency (rf) power density were systematically studied by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. We found that at a low rf power density of 16.7 to 20.8 mW/cm3, the structure of silicon thin films evolves from a completely amorphous phase to an intermediate phase containing both amorphous and microcrystalline silicon. As the power density is increased to a moderate value of 25 mW/cm3, a highly crystallized (111)-preferred hydrogenated microcrystalline silicon (μc-Si:H) film featuring a vertically aligned cone-shaped structure, is emerging. Both the crystallinity and deposition rate exhibit a monotonic increase with the increase in the rf p...

Dilution effect of Ar/H2 on the microstructures and photovoltaic properties of nc-Si:H deposited in low frequency inductively coupled plasma

This work reports upon the dilution effect of Ar + H2 on the microstructures, optical, and photovoltaic properties of the hydrogenated nanocrystalline silicon (nc-Si:H) thin films. High crystallinity (up to 82.6%) nc-Si:H thin films were fabricated from silane diluted by Ar + H2 in a low-frequency inductively coupled plasma (LFICP) facility at a low temperature of 300 °C. The substitution of H2 by Ar in the diluent gas leads to an increase of the deposition rate, grain size, and crystallinity, and a decrease of the optical bandgap. Varying the Ar content caused a fluctuation of the H concentration and a change of the preferential orientation from (111) to (220) in the synthesized thin films. These effects physically originated from changes of the Ar + H2 + SiH4 plasma environment in the LFICP system. The enhancement of the dissociation of SiH4/H2 molecules by ion Ar+ and the metastable state Ar* were discussed in terms of related chemical reactions between the diluent gases and silane. Furthermore, it was...

Self-organized ZnO nanodot arrays : effective control using SiNx interlayers and low-temperature plasmas.

An advanced inductively coupled plasma (ICP)-assisted rf magnetron sputtering deposition method is developed to synthesize regular arrays of pear-shaped ZnO nanodots on a thin SiNx buffer layer pre-deposited onto a silicon substrate. It is shown that the growth of ZnO nanodots obey the cubic root-law behavior. It is also shown that the synthesized ZnO nanodots are highly-uniform, controllable by the experimental parameters, and also feature good structural and photoluminescent properties. These results suggest that this custom-designed ICP-based technique is very effective and highly-promising for the synthesis of property- and size-controllable highly-uniform ZnO nanodots suitable for next-generation light emitting diodes, energy storage, UV nanolasers, and other applications.

Crystalline silicon surface passivation by intrinsic silicon thin films deposited by low-frequency inductively coupled plasma

Amorphous and microcrystal hydrogenated intrinsic silicon (a-Si:H/μc-Si:H) thin films with good silicon surface passivation effect were deposited using a precursor gases of silane and hydrogen, which were discharged by low frequency inductively coupled high density plasma source. With regard to silicon surface passivation, the effect of discharge power on thin films properties, including the optical band gap, the crystal fraction, and bond configuration, as well as the deposition rate were thoroughly investigated. It was found that the best passivation effect was obtained at the region near the transition regime from a-Si:H to μc-Si:H with a minimized incubation layer between the passivation layer and substrate. Cz-silicon wafer passivated by as-deposited μc-Si:H thin films without any post-deposition thermal annealing possesses minority carrier lifetime of about 234 μs. This is attributed to the chemical annealing from the high-density hydrogen plasma during the deposition process. Subsequent thermal ann...

Growth of SiC nanoparticle films by means of RF magnetron sputtering

Plasma radio frequency (RF) magnetron sputtering growth of SiC nanoparticle films on AlN buffered Si(100) is investigated under different reactive gas flows. Introduction of hydrogen into the growth is found to yield a strongest photoluminescence (PL) at 620 nm. If the hydrogen gas flow is zero, or replaced by methane, the PL intensity decreases and the peak is red-shifted to round 680 and 660 nm. These results are discussed in relation to the morphological, compositional, and structural analysis.

Amorphous/crystalline silicon heterojunction solar cells via remote inductively coupled plasma processing.

Low-frequency inductively coupled plasma (ICP) has been widely used to deposit amorphous or microcrystalline Si thin films, but the intrinsic drawback namely ion bombardment effect limits its application in Si heterojunction solar cells. In this letter, we redesigned typical ICP and realized a remote plasma deposition with suppressed ion bombardment effect. This remote ICP system enables the synthesis of high quality amorphous Si layers with a compact network and a high hydrogen content (10.5%). By using this remote ICP system, we achieved amorphous/crystalline silicon heterojunction solar cells with an efficiency of 14.1% without any back surface field or textures.

On conductivity type conversion of p-type silicon exposed to a low-frequency inductively coupled plasma of Ar + H2

The treatment of an Ar + H2 plasma generated by a low-frequency inductively coupled plasma system at 500??C introduces an n-type region (of average electron concentration ~1015?cm?3) on a Czochralski p-type substrate, forming a deep p?n junction. Examination by an electron microscope shows that the plasma treatment produces uniform nanocones on the surface and some defects, such as dislocations and platelets, in the subsurface. All these observed results are hydrogen-related. The conductivity type conversion is due to the formation of hydrogen-enhanced oxygen-related thermal donors (OTDs) as well as hydrogen-incorporated shallow thermal donors. The OTD-related signals are directly observed in the infrared absorption spectra. Both donors are annihilated after annealing at 550??C for 10?min, resulting in conductivity recovery from n-type to original p-type. The electrical properties of the as-formed junction are investigated using current versus voltage (I?V), capacitance versus voltage (C?V) and Hall effect measurements. On this basis, the junction depth, carrier profile and hydrogen diffusion behaviour are studied. Moreover, a clear photovoltaic effect of the junction has been observed through the Suns-Voc and illuminated I?V tests.

In situ catalyzation of carbon nanostructures growth in low-frequency inductively coupled plasmas

A low-frequency inductively coupled plasma source has been employed for in situ catalyzed growth of carbon nanostructures. The catalyzing process depends strongly on the plasma parameters and controls the shape and alignment of nanostructures.

Plasma-enabled growth of ultralong straight, helical, and branched silica photonic nanowires

This article reports on the low-temperature inductively coupled plasma-enabled synthesis of ultralong (up to several millimeters in length) SiO2 nanowires, which were otherwise impossible to synthesize without the presence of a plasma. Depending on the process conditions, the nanowires feature straight, helical, or branched morphologies. The nanowires are amorphous, with a near-stoichiometric elemental composition ([O]/[Si]=2.09) and are very uniform throughout their length. The role of the ionized gas environment is discussed and the growth mechanism is proposed. These nanowires are particularly promising for nanophotonic applications where long-distance and channelled light transmission and polarization control are required.