Low Temperature Vibrational Properties of Amorphous Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
R. S. Crandall ◽  
E. Iwaniczko ◽  
A. H. Mahan ◽  
X. Liu ◽  
R.O. Pohl
Keyword(s):  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Internal Friction ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Amorphous Solids ◽  
Vibrational Properties ◽  
Deposition Method ◽  
Hot Wire

ABSTRACTWe present internal friction and shear modulus measurements of amorphous silicon (a-Si) and germanium (a-Ge) films. The temperature independent plateau in internal friction below 10 K, common to all amorphous solids, also exists in these films. However, its magnitude which depends critically on the deposition method is smaller than found for all other amorphous solids. In particular, hydrogenated a-Si with about 1 at. % H prepared by hot-wire chemical-vapor-deposition leads to an internal friction nearly three orders of magnitude smaller than observed for all other amorphous solids. The internal friction increases after the hydrogen is removed by effusion.

Light-Induced Increase in Two-Level Tunneling States in Hydrogenated Amorphous Silicon

1999 ◽  
Vol 557 ◽  
Author(s):  
Xiao Liu ◽  
R.O. Pohl ◽  
R.S. Crandall
Keyword(s):  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Internal Friction ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Room Temperature ◽  
Hydrogenated Amorphous Silicon ◽  
Chemical Vapor ◽  
Hot Wire ◽  
Hydrogenated Amorphous

AbstractWe observe an increase of the low-temperature internal friction of hydrogenated amorphous silicon prepared by both hot-wire and plasma-enhanced chemical-vapor deposition after extended light-soaking at room temperature. This increase, and the associated change in sound velocity, can be explained by an increase of the density of two-level tunneling states, which serves as a measure of the lattice disorder. The amount of increase in internal friction is remarkably similar in both types of films although the amount and the microstructure of hydrogen are very different. Experiments conducted on a sample prepared by hot-wire chemical-vapor deposition show that this change anneals out gradually at room temperature in about 70 days. Possible relation of the light-induced changes in the low-temperature elastic properties to the Staebler-Wronski effect is discussed.

New Results on the Microstructure of Amorphous Silicon as Observed by Internal Friction

1997 ◽  
Vol 467 ◽  
Author(s):  
R. S. Crandall ◽  
A. H. Mahan ◽  
E. Iwaniczko ◽  
K. M. Jones ◽  
X. Liu ◽  
...  
Keyword(s):  
Internal Friction ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Amorphous Solid ◽  
Amorphous Solids ◽  
Electron Beam Evaporation ◽  
Hot Wire ◽  
Si Films ◽  
Hydrogenated Amorphous

ABSTRACTWe have measured the low temperature internal friction (Q−1) of amorphous silicon (a-Si) films. Electron-beam evaporation leads to the well-known temperature-independent plateau common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H) with about 1 at.% H produced by hot wire chemical vapor deposition, however, the value of is over two hundred times smaller than for e-beam a-Si. This is the first observation of an amorphous solid without any significant low energy excitations. This finding offers the opportunity to study amorphous solids containing controlled densities of tunneling defects, and thus to explore their nature.

Elastic Properties of Several Silicon Nitride Films

2007 ◽  
Vol 989 ◽  
Author(s):  
Xiao Liu ◽  
Thomas H Metcalf ◽  
Qi Wang ◽  
Douglas M Photiadis
Keyword(s):  
Chemical Vapor Deposition ◽  
Silicon Nitride ◽  
Internal Friction ◽  
Amorphous Silicon ◽  
Elastic Properties ◽  
Vapor Deposition ◽  
Film Growth ◽  
Chemical Vapor ◽  
Structural Disorder ◽  
Order Of Magnitude

AbstractWe have measured the internal friction (Q-1) of amorphous silicon nitride (a-Si3Nx) films prepared by a variety of methods, including low-pressure chemical-vapor deposition (LPCVD), plasma-enhanced chemical-vapor deposition (PECVD), and hot-wire chemical-vapor deposition (HWCVD) from 0.5 K to room temperature. The measurements are made by depositing the films onto extremely high-Q silicon double paddle oscillator substrates with a resonant frequency of ~5500 Hz. We find the elastic properties of these a-Si3N4 films resemble those of amorphous silicon (a-Si), demonstrating considerable variation, depending on the film growth methods and post deposition annealing. The internal friction for most of the films shows a broad temperature-independent plateau below 30 K, characteristic of amorphous solids. The values of Q-1, however, vary from film to film in this plateau region by more than one order of magnitude. This is typical for tetrehedrally bonded amorphous thin films, like a-Si, a-Ge, and a-C. The PECVD films have the highest Q-1 just like an ordinary amorphous solid, while LPCVD films have an internal friction more than one order of magnitude lower. All the films show a reduction of Q-1 after annealing at 800°C, even for the LPCVD films which were prepared at 850°C. This can be viewed as a reduction of structural disorder.

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