Investigation of structural properties of poly-Si thin films obtained by aluminium induced crystallization in different atmospheres

Fan

Sci. China Phys. Mech. Astron.

et al. 2010

Typically, highly p-doped (2×10 18 cm −3 ) poly-Si films fabricated by the aluminum induced layer exchange (ALILE) process are not suitable for solar cell absorber layers. In this paper, the fabrication of high-quality, continuous polycrystalline silicon (poly-Si) films with lower doping concentrations (2×10 16 cm −3 ) using aluminum-induced crystallization (AIC) is reported. Secondary-ion-mass spectroscopy (SIMS) results showed that annealing at different temperature profiles leads to a variety of Al concentrations. Hall Effect measurements revealed that Al dopant concentration depends on the annealing temperature and temperature profile. Raman spectral analysis indicated that samples prepared via AIC contain some regions with small grains. polycrystalline silicon, low doping concentration, AIC, crystallizationThe crystallization of amorphous silicon (a-Si) deposited on glass substrates is gaining increasing interest for its importance in polycrystalline silicon (poly-Si) thin film solar cells [1]. One of the most important challenges for the development of polycrystalline silicon (poly-Si) thin film solar cells on glass substrates is the growth of crystalline silicon at low-temperature. A promising means to overcome this problem is the deposition of a-Si followed by subsequent low-temperature crystallization. The crystallization techniques that attracting most attention so far have been the solid phase crystallization (SPC) [2], laser crystallization (LC) [3], and rapid photo-thermal crystallization (RTP) [4]. As an alternative approach, metal-induced crystallization (MIC) has caught considerable interest, because the crystallization temperature of a-Si are much lower than reported temperature for SPC of a-Si of about 600°C. When a-Si is in contact with certain metal, remarkably, the crystallization temperature is well below the eutectic temperature of the corresponding metal/Si system [5]. In MIC of silicon, the silicide forming and nonsilicide forming crystallization is distinguishable. In contrast to compound forming systems (e.g. Ni/Si, Cu/Si, and Ag/Si, etc.), simple eutectic systems, such as Al/Si (AIC), do not form stable silicides [6]. The Al/Si system does not form a stable silicide; a lower crystallization temperature can be achieved [7]. For Al/Si system, the crystallization temperatures as low as 100°C has been reported [8]. The mechanism for AIC is the aluminum-induced layer exchange (ALILE) process which was first introduced by Nast et al. [9]. Annealing of a glass/Al/a-Si composite layer at temperature below the eutectic temperature of the Al/Si system (577°C) leads to the formation of a glass/poly-Si/Al(+Si) composite layer. During the annealing, silicon atoms diffuse into the aluminum layer and then nucleate in the aluminum matrix. The nuclei grow in all directions until confined within the aluminum layer between the glass and the a-Si layer. Crystal growth then continues in a lateral direction only until adjacent crystallites form a continuous poly-Si layer. The

Section: Resultsmentioning

confidence: 99%

Poly-Si films with low aluminum dopant containing by aluminum-induced crystallization

Fan

Sci. China Phys. Mech. Astron.

et al. 2010

“…25 More recent reports have studied aluminum-induced crystallization in this materials system. 26,27 The mechanical properties of the metastable phase, formed during RT deposition with Si concentrations >45 at.%, were also examined recently. 28 The results of the Scherrer formula calculations, used to estimate the crystallite size from x-ray patterns, showed a decrease of the Al nanocrystallite size with increasing Si concentration.…”

Section: Resultsmentioning

confidence: 99%

Combinatorial investigation of the mechanical properties of aluminum-silicon thin film nanocomposites

2007

We have undertaken the exploration of Al x Si 1−x material systems to discover new alloys with enhanced mechanical properties. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined through indentation experiments by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes. In samples with an Al concentration near 55 at.%, the data show that decreasing the Al crystallite size by nearly one half increases the nanocomposite hardness by nearly a factor of two.

“…Annealing in different atmospheres lead to different morphological structures due to different stages in the crystallization of the poly-Si crystallites, as reported in. 10 Generally, it is observed by optical reflection microscopy that the annealing in vacuum, vacuum + air and N 2 + H 2 leads to a decrease of the size of the a-Si areas, thus indicating the formation of more uniform poly-Si layer. CPM grey level height image and AFM image (Figs.…”

Section: Characterization Of the Poly-si Layersmentioning

confidence: 99%

“…The layers are then isothermally annealed in the following atmospheres: (i) air at 540 C for 3 h, (ii), vacuum (10 −3 -10 −4 Pa) at 550 C for 4 h, (iii) vacuum and subsequently in air (the same conditions as in (i) and (ii)), and (iv) N 2 + H 2 (forming gas) at 530 C for 4 h. The crystalline structure of the poly-Si films is improved when the annealing is performed in an atmosphere containing H 2 as shown in. 10 It is supposed that the presence of H 2 stimulates the crystalline grain growth during the process of AIC by increasing the diffusion rate of Al and Si. The poly-Si layers obtained are not chemically treated (etched) before HA deposition and therefore Al inclusions are present on the surfaces.…”

Section: Poly-si Preparationmentioning

confidence: 99%

“…Poly-Si layers are formed at low temperature, in comparatively short periods of time, by aluminum induced crystallization (AIC). 9 10 We demonstrate a time-saving method for the fabrication of structures organized on both a micro-and nanoscale typically found in nature, by using laser light. In the applied LLSI method, laser irradiation of the poly-Si surfaces leads to the creation of micrometer scale architecture with precisely controlled size and shape, and a subsequent growth of nanostructured HA.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Bioactivity of Polycrystalline Silicon Layers

Pramatarova¹,

Pecheva²,

Montgomery³

et al. 2008

j nanosci nanotechnol

After oxygen, silicon is the second most abundant element in the environment and is present as an impurity in most materials. The widespread occurrence of siliceous biominerals as structural elements in lower plants and animals suggests that Si plays a role in the production and maintenance of connective tissue in higher organisms. It has been shown that the presence of Si is necessary in bones, cartilage and in the formation of connective tissue, as well as in some important metabolic processes. In this work, polycrystalline silicon layers are tested in terms of bioactivity, i.e., their ability to induce hydroxyapatite formation from simulated body fluid. Hydroxyapatite is a biologically compatible material with chemical similarity to the inorganic part of bones and teeth. Polycrystalline silicon layers are obtained by aluminum induced crystallization of Al and amorphous Si thin films deposited sequentially on glass substrates by radio-frequency magnetron sputtering and subsequently annealed in different atmospheres. The hydroxyapatite formation is induced by applying a method of laser-liquid-solid interaction. The method consists of irradiating the samples with laser light while immersed in a solution that is supersaturated with respect to Ca and P. As a result, heterogeneous porous sponge-like carbonate-containing hydroxyapatite is grown on the polysilicon surfaces. Crystals that are spherical in shape, containing Ca, P and O, Na, Cl, Mg, Al, Si and S, as well as well-faceted NaCl crystals are embedded in the hydroxyapatite layer. Enhancement of the hydroxyapatite growth and increased crystallinity is observed due to the applied laser-liquid-solid interaction.