Defect Formation Mechanism During PECVD of a-Si:H

1997 ◽  
Vol 467 ◽  
Author(s):  
Keiji Maeda ◽  
Ikurou Umezu
Keyword(s):  
Formation Mechanism ◽  
Urbach Energy ◽  
Defect Formation ◽  
Defect Density ◽  
Reaction Energy ◽  
Mobility Edge ◽  
Weak Bond ◽  
Bond Density ◽  
Extra Energy ◽  
Staebler Wronski Effect

ABSTRACTDefect formation mechanism in a-Si:H during PECVD at substrate temperature below 250°C is considered to be breaking of weak bonds in the Urbach tail. To break weak bonds, an extra energy is necessary. This energy is supplied by the reaction energy of SiH3 precursor at the growing surface incorporating SiH2 into the network. The defect density is experimentally shown to be proportional to a product of the energy supply frequency, i.e., SiH2 density, and the weak bond density which is obtained by the Urbach energy. By analysis using the configurational coordinate diagram the energy level of the broken weak bond is determined to be 0.2 eV above the valence band mobility edge. There is similarity of the defect formation mechanism during deposition to that of the Staebler-Wronski effect.

Simultaneous Relaxation of Network and Defects in Silicon-Implanted a-Si:H

1995 ◽  
Vol 377 ◽  
Author(s):  
J. Nakata ◽  
S. Sherman ◽  
S. Wagner ◽  
P. A. Stolk ◽  
J. M. Poate
Keyword(s):  
Electronic Transport ◽  
Annealing Temperature ◽  
Urbach Energy ◽  
Defect Density ◽  
Dark Conductivity ◽  
Equilibrium Theory ◽  
Hopping Conduction ◽  
Dangling Bond ◽  
Bond Density ◽  
Additional Illumination

ABSTRACTWe report extensive optical and electronic transport data on silicon-implanted a-Si:H, annealed in steps in the dark or with additional illumination. All measured properties relax gradually with increasing annealing temperature. The dark conductivity of the as-implanted film is dominated by hopping conduction via midgap defects. This channel is pinched off during the initial stages of annealing. The midgap defect density and the Urbach energy follow an annealing path that agrees qualitatively with the trajectory postulated by the equilibrium theory of the dangling-bond density. Therefore, the silicon network and the defect density equilibrate continuously during network relaxation.

Deposition, Defect and Weak Bond Formation Processes in a-Si:H

1998 ◽  
Vol 507 ◽  
Author(s):  
J Robertson ◽  
M J Powell
Keyword(s):  
Hydrogen Evolution Reaction ◽  
Surface Defect ◽  
Defect Formation ◽  
Defect Density ◽  
Bond Formation ◽  
Surface Processes ◽  
Formation Processes ◽  
Weak Bond ◽  
Further Development ◽  
Surface Defect Density

ABSTRACTThe growth of a-Si:H and the resulting weak bond and defect formation mechanism is analysed in terms of the adsorbed Sill3 model of growth. It is found that this model describes the surface processes well, but it needs further development to correctly describe the temperature dependence of the formation of defects and weak bonds, since the surface defect density decreases monotonically with temperature and does not show a minimum near 250C. We show that the experimentally observed increase in hydrogen content, weak bond and defect density at lower deposition temperatures can be accounted for by a hydrogen evolution reaction from H2* sites.

The Effect of Post-Deuteration on Metastability in a-Si:H

1993 ◽  
Vol 297 ◽  
Author(s):  
N.H. Nickel ◽  
W.B. Jackson ◽  
C.C. Tsai
Keyword(s):  
Defect Formation ◽  
Chemical Potential ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Deuterium Plasma ◽  
Bond Density ◽  
Intense Light ◽  
Hydrogenated Amorphous ◽  
Metastable Defect

Hydrogenated amorphous silicon films were deuterated through a sequence of 1h exposures to a remote deuterium plasma at 350°C. The concentration profiles of hydrogen and deuterium were determined by SIMS at various times during the exposure sequence. The defect density in state A, after deuteration and after illumination with white light were determined using CPM measurements following each 1h exposure sequence. We find that post-deuteration does not alter the defect density in state A, change the Urbach edge, nor significantly alter metastable defect formation. Intense light soaking increases the defect density by about 5 × 10l6cm−3 independent of the total H + D concentration. These results suggest that D always enters the sample in pairs pinning the hydrogen chemical potential which supports the idea of a negative U system for hydrogen and deuterium. Despite an increase of Si-H bonds by as much as 3 × 1021cm−3, the annealed dangling bond density and the weak Si-Si bond density did not change.This suggests that the density of weak Si-Si bonds as well as the dangling bond density is determined by equilibration with strong Si-Si bonds through the interchange of H. The implications of these results for H bonding will be discussed.

Defect Formation During Deposition of Undoped a-Si:H BY PE-CVD

1996 ◽  
Vol 420 ◽  
Author(s):  
Keiji Maeda ◽  
Ikurou Umezu
Keyword(s):  
Surface Reaction ◽  
Defect Formation ◽  
Defect Density ◽  
Bimolecular Reaction ◽  
Enthalpy Change ◽  
Defect Concentration ◽  
Deposition Condition ◽  
Atom Concentration ◽  
Deposition Parameters ◽  
Staebler Wronski Effect

AbstractDependence of the as-grown defect concentration in PECVD undoped a-Si:H on the deposition parameters, i.e., substrate temperature and precursor density in the plasma produced by H2 dilution of SiH4 gas, is investigated. It is found that the defect density behaves similarly to the concentration of SiH2 configuration in the films deposited at substrate temperatures below 300 °C. The defect concentration, however, varies proportionally to about the 3rd to 4th power of the SiH2 concentration depending on the deposition condition. Based on the surface reaction mechanism proposed in our previous paper, a large enthalpy change is expected to accompany the bimolecular reaction of the adsorbed SiH3 radicals, which incorporates the SiH2 configuration into the network. Characteristics of the defect formation caused by tile breaking Si-Si bond near the growing surface owing to this energy is compared with those of the Staebler-Wronski effect. Both similarity in dependence on II atom concentration and difference in annealing temperature are discussed. It is concluded that the as-grown defects are most likely formed during deposition owing to the large enthalpy change accompanying the bimolecular surface reaction.

H NMR Evidence for a Change in The Local Hydrogen Environment of Sites Associated with the Staebler-Wronski Effect in a-Si:H

2002 ◽  
Vol 715 ◽  
Author(s):  
T. Su ◽  
Robin Plachy ◽  
P. C. Taylor ◽  
S. Stone ◽  
G. Ganguly ◽  
...  
Keyword(s):  
Line Shape ◽  
Defect Density ◽  
Hydrogen Atoms ◽  
Hydrogen Environment ◽  
H Nmr ◽  
Line Shapes ◽  
Different Temperatures ◽  
Staebler Wronski Effect

AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.

The Defect Formation Mechanism Associated with Low Dose Implants into Si Fin Structures

2018 ◽  
Author(s):  
Kevin Jones ◽  
Emily Turner ◽  
Jae Young Lee ◽  
Hans van Meer ◽  
Naushad Variam ◽  
...  
Keyword(s):  
Formation Mechanism ◽  
Low Dose ◽  
Defect Formation

scholarly journals Beta Fleck formation in Titanium Alloys

2020 ◽  
Vol 321 ◽  
pp. 10001
Author(s):  
K. Kelkar ◽  
A Mitchell
Keyword(s):  
Titanium Alloys ◽  
Formation Mechanism ◽  
Defect Formation ◽  
Melting Rate ◽  
Vacuum Arc ◽  
Formation Mechanisms ◽  
Alloy Development ◽  
Vacuum Arc Remelting ◽  
Freckle Formation ◽  
Nickel Base

Beta fleck is a troublesome segregation defect in many titanium alloys. It has previously been investigated by several authors and appears to have two formation mechanisms, one similar to that of “freckle” in steels and nickel-base alloys, the other arising in the “crystal rain” effect seen in conventional steel ingots. The freckle defect has been extensively studied and several theories developed to account for its formation in both remelted ingots and directional castings. In this work we compare the findings of investigations into the nickel-base freckle formation mechanism to similar conditions in the vacuum arc remelting of titanium alloys. We find that there are strong similarities between the beta fleck formation conditions and the parameters related to the Rayleigh Number criterion for freckle formation. In particular, the dendritic solidification parameters and the density dependence on segregation coefficients both fit well with the conditions proposed to characterise freckle formation. The second formation mechanism arises in the columnar to equiax transition in solidification. The condition for the avoidance of the defect in the two cases is the shown to be the same, namely the use of a very low VAR melting rate, but that it is unlikely to be 100% successful in preventing defect formation. We propose that the techniques presently in use for alloy development in the superalloy field through optimising the composition for minimum sensitivity to freckle formation should be applied to the formulation of future titanium alloys; also that attention should be paid to developing the PAM process to provide suitable solidification conditions for defect absence in a final ingot.

Effects of nano-copper particles on the properties of Sn58Bi composite solder pastes

2017 ◽  
Vol 34 (1) ◽  
pp. 40-44 ◽  
Author(s):  
Hao Zhang ◽  
Yang Liu ◽  
Fenglian Sun ◽  
Gaofang Ban ◽  
Jiajie Fan
Keyword(s):  
Formation Mechanism ◽  
Composite Solder ◽  
Defect Formation ◽  
Void Formation ◽  
Experimental Results ◽  
Solder Paste ◽  
Content Type ◽  
Weight Percentage ◽  
Copper Particles ◽  
Solder Pastes

Purpose This paper aimed to investigate the effects of nano-copper particles on the melting behaviors, wettability and defect formation mechanism of the Sn58Bi composite solder pastes. Design/methodology/approach In this paper, the mechanical stirring method was used to get the nano-composite solder pastes. Findings Experimental results indicated that the addition of 3 wt.% (weight percentage) 50 nm copper particles showed limited effects on the melting behaviors of the Sn58Bi composite solder paste. The spreading rate of the Sn58Bi composite solder paste showed a decreasing trend with the increase of the weight percentage of 50 nm copper particles from 0 to 3 wt.%. With the addition of copper particles of diameters 50 nm, 500 nm or 6.5 μm into the Sn58Bi solder paste, the porosities of the three types of solder pastes showed a similar trend. The porosity increased with the increase of the weight percentage of copper particles. Based on the experimental results, a model of the void formation mechanism was proposed. During reflow, the copper particles reacted with Sn in the matrix and formed intermetallic compounds, which gathered around the voids produced by the volatilization of flux. The exclusion of the voids was suppressed and eventually led to the formation of defects. Originality/value This study provides an optimized material for the second and third level packaging. A model of the void formation mechanism was proposed.

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