The relationship between the film properties and the preparation conditions for a-Si:H grown by homogeneous chemical vapour deposition

Toneva, A.; Mihailova, T.; Danesh, P.; Pantchev, B. I.

doi:10.1088/0268-1242/9/12/021

Cited by 6 publications

(6 citation statements)

References 14 publications

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“…The i-cSi-o also shows the stop-band reflection and the second-band and third-band reflections, although the positions are blue-shifted from those of i-aSi-o, consistent with the difference of refractive index between amorphous Si (n % 4.0) and crystalline Si (n % 3.45). [24] Notably, the position of the third band corresponds to the energy of the full photonic band gap according to theoretical calculations, [14] and its existence implies that both i-aSi-o and i-cSi-o have retained the good structural order of the silica opal. The inset in the SEM image further supports the high structural quality of i-cSi-o.…”

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Tailoring the Electrical Properties of Inverse Silicon Opals ‐ A Step Towards Optically Amplified Silicon Solar Cells

et al. 2009

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It has been just over two decades since John and Yablonovitch theoretically predicted the existence of a complete photonic band gap in 3D silicon photonic crystals, a range of wavelengths for which light is forbidden to propagate in all three spatial dimensions.[1] This breakthrough inspired global research activity to transform the idea into practice, at the time driven mainly by the field of optical telecommunications.[2] Since then, several studies have demonstrated the potential advantages of photonic crystals for other applications, such as light emitting diodes, [3] lasers, [4,5] wave guides, [6,7] photocatalysts, [8] displays, [9,10] and solar cells. [11][12][13] In particular, the inverse silicon opal (i-Si-o) with a high refractive-index contrast has attracted attention because of its demonstrated complete photonic band gap at 1.5 mm and the possibility of large-scale synthesis.[14] While the optical properties of i-Si-o have been thoroughly investigated, [15,16] little research has been focused on its electrical behaviour, knowledge that would underpin the development of any kind of electro-optical device based on i-Si-o. It can be envisioned that the electrical properties of i-Si-o with its 3D open-framework microstructure could be very different from that of Si thin films, similar to the different behaviour observed for electrochemically etched porous silicon.[17] It is therefore our opinion that the electrical properties of i-Si-o need to be elucidated, as this data will be critical for applications such as optically amplified silicon solar cells. [18] The purpose of the work described herein is to understand the electrical properties of i-Si-o, focusing in particular on the influence of the photonic-crystal lattice constant and the effect of crystallinity and hydrogen-plasma passivation of Si on the electrical conductivity of i-Si-o, and how these material properties correlate with the optical properties of i-Si-o.To reach our objectives, we fabricated i-Si-o by infiltrating the voids of a silica-opal template with Si using chemical vapor deposition (CVD), and subsequently etching the silica spheres with hydrofluoric acid (HF).[19] Accurate measurements of the dc electrical dark conductivities (s d ) require electrodes and electrical contacts on the i-Si-o films. Therefore, instead of using glass substrates, which are most commonly employed, we prepared all samples on sapphire substrates due to their high stability against HF etching. Note that the i-Si-o fabricated on glass substrates usually gets detached and becomes free-standing after HF etching, while high-quality intact i-Si-o films can be achieved on sapphire substrates.The as-deposited Si obtained by CVD in the interstitial voids of silica opals is amorphous. We denote them inverse amorphoussilicon opals (i-aSi-os). In order to integrate i-aSi-o in optical, electro-optical, or electrical devices, it is important to achieve inverse crystalline-silicon opals (i-cSi-o), because crystalline silicon has a much higher conductivity than amorphous s...

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Tailoring the Electrical Properties of Inverse Silicon Opals ‐ A Step Towards Optically Amplified Silicon Solar Cells

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“…There are two mechanisms for the penetration of sodium into the growing a-Si : H film: thermal diffusion and field-induced diffusion. The diffusion coefficient of sodium in a-Si : H at a deposition temperature of 563 K is 1.36 X lo-" m2 s -' (Zhang and Haneman 1987). This value is high enough to make the contribution of the thermal component significant.…”

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confidence: 94%

“…The increased room-temperature conductivity and the lower values of activation energy in a-Si : H deposited on soda-lime glass substrates indicate that these films are doped with sodium. It has been suggested that sodium penetrates into the a-Si : H film during its growth and acts as a donor (Zhang andHaneman 1987, Nesheva and. The decrease in electrical conductivity and increase in activation energy on increasing the micropore density suggest that the doping level depends upon the amount of micropores and becomes lower in films with a higher porosity.…”

Section: Results and Disc~jssionmentioning

confidence: 99%

“…Such optical waveguides and waveguide structures are fabricated in glass substrates containing alkali ions. However, it has been demonstrated that deposition of a-Si : H on soda-lime glass leads to the appearance of electrical metastability, which has unambiguously been attributed to sodium contamination of the film (Zhang andHaneman 1987, Nesheva and. Sodium penetrates into a-Si: H through the fildsubstrate interface and therefore the structure of the grown film could play an essential role in this process.…”

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confidence: 99%

“…Films of a-Si : H prepared by plasma-enhanced chemical vapour deposition (PECVD) are porous and many material properties depend upon the amount of micropores. It has been established that micropores are present even in device-grade material and their number is correlated to hydrogen-bonding configurations and other structural properties (Danesh and Pantchev 1988, Danesh, Toneva, Pantchev and Kudeyarova 1990, Danesh, Pantchev, Savatinova, Liarokapis and Raptis 1991, Toneva, Mihailova, Danesh and Pantchev 1994. Therefore, the question arises as to whether there is a correlation between the amount of micropores in a-Si : H films and the penetration of sodium from the soda-lime substrate.…”

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Hydrogenated amorphous silicon on soda-lime glass substrate: Correlation between sodium contamination and porosity of the films

Pantchev

Danesh

1995

Philosophical Magazine A

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A New Synthetic Approach to Silicon Colloidal Photonic Crystals with a Novel Topology and an Omni‐Directional Photonic Bandgap: Micromolding in Inverse Silica Opal (MISO)

et al. 2003

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The fabrication of photonic crystals based on colloidal crystal templating represents one of the most attractive approaches among those currently being considered to overcome the challenge of building up a 3D periodic modulation of refractive index at the micrometer length scale. [1,2] So far, important advances have been made by using micrometer-size silica or latex sphere colloidal crystals, i.e., artificial opals, as templates. Briefly, opal molds are built from a suspension of colloidal particles either by sedimentation on a flat substrate, [3] which gives rise to large size face-centered cubic (fcc) crystals, or by convection-force induced self-assembly, which results in planarized fcc crystals of controlled thickness. [4] By infiltrating the interstitial sites of these structures with high refractive index materials, such as silicon, [5,6] germanium, [7,8] or titanium oxide, [9,10] and later removal of the colloidal crystal scaffold, an inverted opal structure consisting of interconnected air cavities in a high dielectric constant medium is attained. This chemical approach to the fabrication of photonic crystals leads to optical-quality materials with the suitable geometry, topology, and dielectric contrast as to allow the opening of photonic bandgaps.[11]In this same context, it has also been demonstrated that it is possible to synthesize a new type of colloidal crystal made of a wide variety of dense and porous oxides and metals by means of a template approach that utilizes a mold consisting of a periodic distribution of interconnected spherical cavities in a latex background, which is obtained by replicating a silica colloidal crystal in latex and subsequently dissolving the silica template. [12,13] Infiltration of different precursors is used to coat the internal surfaces of the latex mold with different materials and gives rise to a novel kind of hybrid inverse colloidal crystal. The method has been referred to as micromolding in inverse polymer opals (MIPO), and while the approach is quite versatile, it cannot be easily applied to obtain compositions whose synthesis requires high temperatures or corrosive precursors.Here, we present a new type of silicon colloidal photonic colloidal crystal presenting a different topology than previously synthesized high refractive index contrast colloidal photonic crystals. It has been built using a new process of colloidal crystal templating based on micromolding in inverse silica opals (MISO), i.e., interconnected air cavities in a silica matrix. By chemical vapor deposition (CVD) of disilane within this lattice we form a continuous silicon layer of controlled thickness that coats the walls of the silica matrix. Later, by dissolution of the starting inverted silica opal it is possible to obtain fcc silicon colloidal photonic crystals with a topology never observed before, and which present a full photonic bandgap, as indicated by theoretical photonic band structure calculations.Samples employed in this study were prepared as follows. The silica micromold was first ...

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The relationship between the film properties and the preparation conditions for a-Si:H grown by homogeneous chemical vapour deposition

Cited by 6 publications

References 14 publications

Tailoring the Electrical Properties of Inverse Silicon Opals ‐ A Step Towards Optically Amplified Silicon Solar Cells

Tailoring the Electrical Properties of Inverse Silicon Opals ‐ A Step Towards Optically Amplified Silicon Solar Cells

Hydrogenated amorphous silicon on soda-lime glass substrate: Correlation between sodium contamination and porosity of the films

A New Synthetic Approach to Silicon Colloidal Photonic Crystals with a Novel Topology and an Omni‐Directional Photonic Bandgap: Micromolding in Inverse Silica Opal (MISO)

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