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.

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.

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.

Molecular Hydrogen in Hot-Wire Hydrogenated Amorphous Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
Xiao. Liu ◽  
E. Iwaniczko ◽  
R.O. Pohl ◽  
R.S. Crandall
Keyword(s):  
Internal Friction ◽  
Amorphous Silicon ◽  
Molecular Hydrogen ◽  
Solid Phase ◽  
Hydrogenated Amorphous Silicon ◽  
Chemical Vapor ◽  
Amorphous Solid ◽  
Hot Wire ◽  
Hydrogenated Amorphous ◽  
Triple Point Temperature

ABSTRACTWe have studied the elastic properties of hydrogenated amorphous silicon (a-Si:H) prepared by hot wire chemical-vapor deposition (HWCVD). With 1 at.% H, this material has been found to be the only amorphous solid which has a low-temperature internal friction more than two orders of magnitude smaller than all other amorphous solids studied to date, as reported recently. As the hydrogen concentration increases above 1 at.%, a broad relaxation peak in internal friction around 5 K is observed. Even more striking is an extremely narrow peak in internal friction accompanied by a discontinuous change in the sound velocity at 13.8 K, which coincides with the triple point temperature of molecular hydrogen. Evidences are provided to show that this anomaly is caused by bulk molecular hydrogen which undergoes a liquid-solid phase transition. This is the first observation for the existence of bulk H2 in HWCVD a-Si:H.

Comparison of Characteristics of Rapid Thermal and Microwave Annealed Amorphous Silicon Thin Films Prepared by Electron Beam Evaporation and Low Pressure Chemical Vapor Deposition

2013 ◽  
Vol 663 ◽  
pp. 372-376
Author(s):  
Chi Hua Hsieh ◽  
Li Te Tsou ◽  
Sheng Hao Chen ◽  
Huai Yi Chen ◽  
Yao Jen Lee ◽  
...  
Keyword(s):  
Electron Beam ◽  
Chemical Vapor Deposition ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Electron Beam Evaporation ◽  
Silicon Thin Films ◽  
Pressure Chemical ◽  
Si Films ◽  
The Cost

In this study we use chemical and physical vapor depositions to fabricate amorphous silicon (a-Si) films. We also use traditional rapid thermal annealing (RTA) and advanced microwave annealing (MWA) to activate or crystallize a-Si films and then observe their sheet resistances and crystallization. We discovered, although the cost of films fabricated by electron beam (e-beam) evaporation is relatively lower than by chemical vapor deposition (CVD), the effects of the former method are poorer whether in sheet resistance or film crystallization. In addition, only at the doping layer prepared by CVD can film crystallization degree produced by MWA match RTA.

High Voltage Amorphous Silicon Solar Cells by Hot-Wire Chemical Vapor Deposition

2002 ◽  
Vol 715 ◽  
Author(s):  
Qi Wang ◽  
Eugene Iwaniczko
Keyword(s):  
Phase Transition ◽  
Chemical Vapor Deposition ◽  
Amorphous Silicon ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Open Circuit ◽  
Hot Wire ◽  
Steel Substrates ◽  
Hydrogenated Amorphous ◽  
P Cells

AbstractWe have achieved the best open-circuit voltage (Voc = 0.94 V) to-date in hydrogenated amorphous silicon (a-Si:H) photovoltaic cells deposited entirely by hot-wire chemical vapor deposition. The fill factor (FF = 0.74) remained high and a current density of 8-9 mA/cm2 with about 1800 Å i-layer was obtained in our n-i-p cells on untextured stainless-steel substrates. The Voc improvement of about 60 mV in compared to our previous best Voc was obtained by incorporating materials grown with H-dilution close to the phase transition from amorphous to microcrystalline silicon in the i-layer and at the i-p interface. A low substrate temperature of 150°C for the i-layer was also essential, most likely to widen the bandgap of the i-layer. A brief atomic H-treatment after grown the i-layer increases the Voc further by improving the p-i interface. The last 60 Å of the i-layer before p-layer is extremely close to the transition to microcrystallinity, though it remains mainly amorphous. Our p-layers are also close to the phase transition.

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