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Title: Structural properties of a-Si films and their effect on aluminum induced crystallization

Abstract

In this paper, we report the influence of the structural properties of amorphous silicon (a-Si) on its subsequent crystallization behavior via the aluminum induced crystallization (AIC) method. Two distinct a-Si deposition techniques, electron beam evaporation and plasma enhanced chemical vapor deposition (PECVD), are compared for their effect on the overall AIC kinetics as well as the properties of the final poly-crystalline (poly-Si) silicon film. Raman and FTIR spectroscopy results indicate that the PECVD grown a-Si films has higher intermediate-range order, which is enhanced for increased hydrogen dilution during deposition. With increasing intermediate-range order of the a-Si, the rate of AIC is diminished, leading larger poly-Si grain size.

Authors:
;  [1]; ;  [1];  [2];  [3]
  1. Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Ankara 06800 (Turkey)
  2. (Turkey)
  3. Central Laboratory, Middle East Technical University, Ankara 06800 (Turkey)
Publication Date:
OSTI Identifier:
22492127
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 5; Journal Issue: 10; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ALUMINIUM; CHEMICAL VAPOR DEPOSITION; COMPARATIVE EVALUATIONS; CRYSTALLIZATION; DILUTION; ELECTRON BEAMS; EVAPORATION; FILMS; FOURIER TRANSFORMATION; GRAIN SIZE; HYDROGEN; INFRARED SPECTRA; PLASMA; RAMAN SPECTROSCOPY; SILICON

Citation Formats

Tankut, Aydin, Ozkol, Engin, Karaman, Mehmet, Turan, Rasit, Micro and Nanotechnology Graduate Program, Middle East Technical University, Ankara 06800, and Canli, Sedat. Structural properties of a-Si films and their effect on aluminum induced crystallization. United States: N. p., 2015. Web. doi:10.1063/1.4933193.
Tankut, Aydin, Ozkol, Engin, Karaman, Mehmet, Turan, Rasit, Micro and Nanotechnology Graduate Program, Middle East Technical University, Ankara 06800, & Canli, Sedat. Structural properties of a-Si films and their effect on aluminum induced crystallization. United States. doi:10.1063/1.4933193.
Tankut, Aydin, Ozkol, Engin, Karaman, Mehmet, Turan, Rasit, Micro and Nanotechnology Graduate Program, Middle East Technical University, Ankara 06800, and Canli, Sedat. Thu . "Structural properties of a-Si films and their effect on aluminum induced crystallization". United States. doi:10.1063/1.4933193.
@article{osti_22492127,
title = {Structural properties of a-Si films and their effect on aluminum induced crystallization},
author = {Tankut, Aydin and Ozkol, Engin and Karaman, Mehmet and Turan, Rasit and Micro and Nanotechnology Graduate Program, Middle East Technical University, Ankara 06800 and Canli, Sedat},
abstractNote = {In this paper, we report the influence of the structural properties of amorphous silicon (a-Si) on its subsequent crystallization behavior via the aluminum induced crystallization (AIC) method. Two distinct a-Si deposition techniques, electron beam evaporation and plasma enhanced chemical vapor deposition (PECVD), are compared for their effect on the overall AIC kinetics as well as the properties of the final poly-crystalline (poly-Si) silicon film. Raman and FTIR spectroscopy results indicate that the PECVD grown a-Si films has higher intermediate-range order, which is enhanced for increased hydrogen dilution during deposition. With increasing intermediate-range order of the a-Si, the rate of AIC is diminished, leading larger poly-Si grain size.},
doi = {10.1063/1.4933193},
journal = {AIP Advances},
number = 10,
volume = 5,
place = {United States},
year = {Thu Oct 15 00:00:00 EDT 2015},
month = {Thu Oct 15 00:00:00 EDT 2015}
}
  • Amorphous (a-)Si-based materials always attracted attention of the scientific community, especially after their use in commercial devices like solar cells and thin film transistors in the 1980s. In addition to their technological importance, the study of a-Si-based materials also present some interesting theoretical-practical challenges. Their crystallization as induced by metal species is one example, which is expected to influence the development of electronic-photovoltaic devices. In fact, the amorphous-to-crystalline transformation of the a-SiAl system has been successfully applied to produce solar cells suggesting that further improvements can be achieved. Stimulated by these facts, this work presents a comprehensive study of themore » a-SiAl system. The samples, with Al contents in the ∼0−15 at. % range, were made in the form of thin films and were characterized by different spectroscopic techniques. The experimental results indicated that: (a) increasing amounts of Al changed both the atomic structure and the optical properties of the samples; (b) thermal annealing induced the crystallization of the samples at temperatures that depend on the Al concentration; and (c) the crystallization process was also influenced by the annealing duration and the structural disorder of the samples. All of these aspects were addressed in view of the existing models of the a-Si crystallization, which were also discussed to some extent. Finally, the ensemble of experimental results suggest an alternative method to produce cost-effective crystalline Si films with tunable structural-optical properties.« less
  • We report a detailed study of the mechanisms and energetics of hydrogen (H) insertion into strained Si-Si bonds during H-induced crystallization of hydrogenated amorphous Si (a-Si:H) thin films. Our analysis is based on molecular-dynamics (MD) simulations of exposure of a-Si:H films to H atoms from a H{sub 2} plasma through repeated impingement of H atoms. Hydrogen atoms insert into Si-Si bonds as they diffuse through the a-Si:H film. Detailed analyses of the evolution of Si-Si and Si-H bond lengths from the MD trajectories show that diffusing H atoms bond to one of the Si atoms of the strained Si-Si bondmore » prior to insertion; upon insertion, a bridging configuration is formed with the H atom bonded to both Si atoms, which remain bonded to each other. After the H atom leaves the bridging configuration, the Si-Si bond is either further strained, or broken, or relaxed, restoring the Si-Si bond length closer to the equilibrium bond length in crystalline Si. In some cases, during its diffusion in the a-Si:H film, the H atom occupies a bond-center position between two Si atoms that are not bonded to each other; after the H diffuses away from this bond-center position, a Si-Si bond is formed between these previously nonbonded Si atoms. The activation energy barrier for the H insertion reaction depends linearly on both the initial strain in the corresponding Si-Si bond and a strain factor that takes into account the additional stretching of the Si-Si bond in the transition-state configuration. The role of the H insertion reactions in the structural relaxation of the a-Si:H network that results in disorder-to-order transitions is discussed.« less
  • Thin films of SrBi{sub 4}Ti{sub 4}O{sub 15} (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 deg. C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P{sub r} and a coercive field E{sub c} values of 5.1 {mu}C/cm{sup 2} and 135 kV/cm for themore » film thermally treated in the microwave oven and 5.4 {mu}C/cm{sup 2} and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10{sup 10} switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.« less
  • We study the properties of Si-rich silicon oxide SiO{sub x} (x < 2) films grown on silica substrates by molecular beam deposition, in a wide range of Si content and annealing temperatures. The measured refractive index and absorption coefficient are successfully described using the effective medium approximation and the chemical compositions measured by x-ray photoelectron spectroscopy (XPS). The Si-SiO{sub 2} phase separation and the degree of Si crystallization increase with the annealing temperature; however, even after annealing at 1200 Degree-Sign C, the samples contain a large proportion of suboxides and partially disordered Si. The Si Raman signal and the absorptionmore » coefficient are nearly proportional to the amount of elemental Si provided by XPS. On the other hand, the Si Raman signal is much weaker than it is expected from the amount of elemental Si, which can be explained by the presence of ultra-small Si nanocrystals (diameters < 2 nm) and/or by the difference in the properties of bulk and nanoscale Si. The 1.5-eV photoluminescence (PL) intensity is the highest for annealing at 1100-1150 Degree-Sign C and x = 1.8-1.9. In contrast, the PL quantum yield steadily increases when the intensity of the Si Raman signal decreases. This observation suggests that the Si nanocrystals observed in the Raman spectra are not direct light-emitting centers. The temperatures induced by laser light in these films are surprisingly high, especially at the highest Si content (x {approx} 1.3). The laser-induced temperature (up to {approx}350 Degree-Sign C) substantially down-shifts the Raman band of Si nanocrystals (in our experiments from {approx}518 to {approx}512 cm{sup -1}) and increases the absorption coefficient (by a factor of {approx}1.4).« less
  • Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si{sub 1−x}Sn{sub x}, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si{sub 1−x}Sn{sub x} exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous siliconmore » occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.« less