scholarly journals Amorphous Dielectric Thin Films with Extremely Low Mechanical Loss

2015 ◽  
Vol 60 (1) ◽  
pp. 359-363 ◽  
Author(s):  
X. Liu ◽  
D.R. Queen ◽  
T.H. Metcalf ◽  
J.E. Karel ◽  
F. Hellman
Keyword(s):  
Amorphous Silicon ◽  
Glassy State ◽  
Amorphous Structure ◽  
Dielectric Thin Films ◽  
Disordered Solids ◽  
Amorphous Network ◽  
Covalently Bonded ◽  
Thermal Measurements ◽  
Amorphous Dielectric ◽  
Hydrogenated Amorphous

Abstract The ubiquitous low-energy excitations are one of the universal phenomena of amorphous solids. These excitations dominate the acoustic, dielectric, and thermal properties of structurally disordered solids. One exception has been a type of hydrogenated amorphous silicon (a-Si:H) with 1 at.% H. Using low temperature elastic and thermal measurements of electron-beam evap-orated amorphous silicon (a-Si), we show that TLS can be eliminated in this system as the films become denser and more structurally ordered under certain deposition conditions. Our results demonstrate that TLS are not intrinsic to the glassy state but instead reside in low density regions of the amorphous network. This work obviates the role hydrogen was previously thought to play in removing TLS in a-Si:H and favors an ideal four-fold covalently bonded amorphous structure as the cause for the disappearance of TLS. Our result supports the notion that a-Si can be made a “perfect glass” with “crystal-like” properties, thus offering an encouraging opportunity to use it as a simple crystal dielectric alternative in applications, such as in modern quantum devices where TLS are the source of dissipation, decoherence and 1/f noise.

scholarly journals Impurity-Defect Complexes in Hydrogenated Amorphous Silicon

1990 ◽  
Vol 209 ◽  
Author(s):  
Lin H. Yang ◽  
C. Y. Fong ◽  
Carol S. Nichols
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Defect Complexes ◽  
Amorphous Network ◽  
Pseudopotential Calculations ◽  
Impurity Defect ◽  
Supercell Model ◽  
Hydrogenated Amorphous

ABSTRACTThe two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H) - a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping - have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using firstprinciples self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfoldcoordinated phosphorus and boron at the second neighbor position to a dangling bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H.

First-principles Modeling of Structure, Vibrations, Electronic Properties and Bond Dynamics in Hydrogenated Amorphous Silicon: Theory versus Experiment

2009 ◽  
Vol 1153 ◽  
Author(s):  
Anatoli Shkrebtii ◽  
Ihor Kupchak ◽  
Franco Gaspari
Keyword(s):  
Amorphous Silicon ◽  
Electronic Properties ◽  
First Principles ◽  
Hydrogen Diffusion ◽  
Hydrogenated Amorphous Silicon ◽  
Amorphous Structure ◽  
Material Structure ◽  
Electron Charge Density ◽  
Wide Range ◽  
Hydrogenated Amorphous

AbstractWe carried out extensive first-principles modeling of microscopic structural, vibrational, electronic properties and chemical bonding in hydrogenated amorphous silicon (a-Si:H) in a wide range of hydrogen concentration and preparation conditions. The theory has been compared with experimental results to comprehensively characterize this semiconductor material. The computer modeling includes ab-initio Molecular Dynamics (MD), atomic structure optimization, advanced signal processing and computer visualization of dynamics. We extracted parameters of hydrogen and silicon bonding, electron charge density and calculated electron density of states (EDOS) and hydrogen diffusion. A good agreement of the theory with various experiments allowed us to correlate microscopic processes at the atomic level with macroscopic properties. Here we focus on correlation of the amorphous structure of the material, atom dynamics and electronic properties. These results are of increasing interest due to extensive application of a-Si:H in modern research and technology and to the significance of detailed understanding of the material structure, bonding, disordering mechanisms and stability.

Anomalous Diffusion of Hydrogen and the Dependence of the Diffusion Constants on Hydrogen Content in Hydrogenated Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
R. Shinar ◽  
H. Jia ◽  
X.-L. Wu ◽  
J. Shinar
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Diffusion Constant ◽  
Relaxation Processes ◽  
Diffusion Constants ◽  
Amorphous Network ◽  
Sputter Deposited ◽  
Hydrogenated Amorphous ◽  
Deposited Film ◽  
Diffusion Of Hydrogen

ABSTRACTThe diffusion constant of hydrogen DH(t) in hydrogenated amorphous silicon (a-Si:H) is strongly dependent on the Si-bonded H content CH of the films. It increases by over four orders of magnitude for CH ranging from 1 to 19 at. %. In an rf sputter-deposited film of CH ∼5 at. % it increases with time at 300 ≤ T ≤ 362°C. The dispersion parameter α in DH(t) = D∞ (ωt)-αis thus negative. This observation and the increase of α with T above a sample-dependent temperature Tτ are discussed in relation to low temperature structural relaxation processes in the amorphous network.

scholarly journals Sputtered Non-Hydrogenated Amorphous Silicon as Alternative Absorber for Silicon Photovoltaic Technology

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6550
Author(s):  
Susana Fernández ◽  
J. Javier Gandía ◽  
Elías Saugar ◽  
Mª Belén Gómez-Mancebo ◽  
David Canteli ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Room Temperature ◽  
Structural Changes ◽  
Continuous Wave ◽  
Low Cost ◽  
Hydrogenated Amorphous Silicon ◽  
Amorphous Structure ◽  
Gas Pressure ◽  
Hydrogenated Amorphous ◽  
Deposition Conditions

Non-hydrogenated amorphous-silicon films were deposited on glass substrates by Radio Frequency magnetron sputtering with the aim of being used as precursor of a low-cost absorber to replace the conventional silicon absorber in solar cells. Two Serie of samples were deposited varying the substrate temperature and the working gas pressure, ranged from 0.7 to 4.5 Pa. The first Serie was deposited at room temperature, and the second one, at 325 °C. Relatively high deposition rates above 10 Å/s were reached by varying both deposition temperature and working Argon gas pressure to ensure high manufacturing rates. After deposition, the precursor films were treated with a continuous-wave diode laser to achieve a crystallized material considered as the alternative light absorber. Firstly, the structural and optical properties of non-hydrogenated amorphous silicon precursor films were investigated by Raman spectroscopy, atomic force microscopy, X-ray diffraction, reflectance, and transmittance, respectively. Structural changes were observed in the as-deposited films at room temperature, suggesting an orderly structure within an amorphous silicon matrix; meanwhile, the films deposited at higher temperature pointed out an amorphous structure. Lastly, the effect of the precursor material’s deposition conditions, and the laser parameters used in the crystallization process on the quality and properties of the subsequent crystallized material was evaluated. The results showed a strong influence of deposition conditions used in the amorphous silicon precursor.

Photoinduced Structural Changes in Hydrogenated Amorphous Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
K. Shimizu ◽  
T. Tabuchi ◽  
K. Hattori ◽  
H. Kida ◽  
H. Okamoto
Keyword(s):  
Amorphous Silicon ◽  
Network Structure ◽  
Structural Changes ◽  
Light Exposure ◽  
Hydrogenated Amorphous Silicon ◽  
Structural Disorder ◽  
Separation Procedure ◽  
Absorption Signal ◽  
Amorphous Network ◽  
Hydrogenated Amorphous

ABSTRACTPolarized electroabsorption method has been used to study photo-induced structural changes in hydrogenated amorphous silicon. The field-modulated absorption signal consists of two components, one of which is the true polarization-dependent electroabsorption serving as an indicator of the structural disorder, and the other is the thermoabsorption resulted from the temperature modulation due to Joule heating. The thermoabsorption component has removed from the observed field-modulated absorption signal to make an accurate and reliable evaluation of structural disorder by phase-separation procedure. As a result, about 15-25 % of the observed signal arises from the thermoabsorption effect for the Tauc gap region. Nevertheless, any essential alteration is not needed for our previous PEA results. The internal stress as well as density have been measured to provide another evidences for the photo-induced structural change. It is found that amorphous silicon film expands and the density tends to decrease upon light-exposure, the temporal behaviors of which coincide with that of the PEA ratio factor indicating disorderness of the amorphous network structure. The results permit us to conclude that a large scaled change in the amorphous network structure occurs under light-exposure, which might proceed the light-induced creation of metastable dangling bond defects.

BONDING IN HYDROGENATED AMORPHOUS SILICON

1981 ◽  
Vol 42 (C4) ◽  
pp. C4-773-C4-777 ◽  
Author(s):  
H. R. Shanks ◽  
F. R. Jeffrey ◽  
M. E. Lowry
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Hydrogenated Amorphous

High Rate Deposition of Stable Hydrogenated Amorphous Silicon in Transition from Amorphous to Microcrystalline Silicon

2003 ◽  
Vol 762 ◽  
Author(s):  
Guofu Hou ◽  
Xinhua Geng ◽  
Xiaodan Zhang ◽  
Ying Zhao ◽  
Junming Xue ◽  
...  
Keyword(s):  
Phase Transition ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Chemical Vapor ◽  
High Rate ◽  
Very High Frequency ◽  
High Quality ◽  
Working Pressure ◽  
Hydrogen Dilution ◽  
Hydrogenated Amorphous

AbstractHigh rate deposition of high quality and stable hydrogenated amorphous silicon (a-Si:H) films were performed near the threshold of amorphous to microcrystalline phase transition using a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The effect of hydrogen dilution on optic-electronic and structural properties of these films was investigated by Fourier-transform infrared (FTIR) spectroscopy, Raman scattering and constant photocurrent method (CPM). Experiment showed that although the phase transition was much influenced by hydrogen dilution, it also strongly depended on substrate temperature, working pressure and plasma power. With optimized condition high quality and high stable a-Si:H films, which exhibit σph/σd of 4.4×106 and deposition rate of 28.8Å/s, have been obtained.

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