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.

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.

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 Study of Optical and Electrical Properties of a-SiC:H for Multi-junction Si Thin Film Solar Cell

2010 ◽  
Vol 1245 ◽  
Author(s):  
Jenny H. Shim ◽  
W.K. Yoon ◽  
S.T. Hwang ◽  
S.W. Ahn ◽  
H.M. Lee
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
High Efficiency ◽  
Open Circuit Voltage ◽  
Defect Density ◽  
Wide Bandgap ◽  
Open Circuit ◽  
Deposition Condition ◽  
Wide Bandgap Material ◽  
Pressure Regime

AbstractStudies have shown that wide bandgap material is required for high efficiency multi-junction solar cell applications. Here, we address proper deposition condition for high quality a-SiC:H films. In high power high pressure regime, we observed that the defect density get much lowered to the similar defect level of a-Si:H film with high H2 dilution. Single junction solar cells fabricated with the optimized condition show high open circuit voltage and low LID effect. The degradation after the LID test was only 13 % reduction of the efficiency indicating that a-SiC:H could be promising material for multi-junction solar cells.

Improved Light Soaking Stability of R.F. Sputter Deposited Amorphous Silicon

1991 ◽  
Vol 219 ◽  
Author(s):  
A. Wynveen ◽  
J. Fan ◽  
J. Kakalios ◽  
J. Shinar
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Initial Defect ◽  
Optical Gap ◽  
Sputter Deposited ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous

ABSTRACTStudies of r.f. sputter deposited hydrogenated amorphous silicon (a-Si:H) find that the light induced decrease in the dark conductivity and photoconductivity (the Staebler-Wronski effect) is reduced when the r.f. power used during deposition is increased. The slower Staebler-Wronski effect is not due to an increase in the initial defect density in the high r.f. power samples, but may result from either the lower hydrogen content or the smaller optical gap found in these films.

DECAHEDRAL AND ICOSAHEDRAL SYMMETRIES: AN APERIODIC MULTIPLE TWINNING MODEL WITH LINEAR STRAINS AND DENSITY INHOMOGENEITY

1992 ◽  
Vol 06 (10) ◽  
pp. 1623-1630 ◽  
Author(s):  
LUIGI G. CONTI
Keyword(s):  
Defect Formation ◽  
Defect Concentration ◽  
Concentration Gradients ◽  
Density Inhomogeneity ◽  
Pure Metals ◽  
And Migration ◽  
Multiple Twinning

The decahedral and icosahedral symmetries often observed in pure metals can be easily explained on the basis of an aperiodic multiple twinning model if defect concentration gradients are present. The different behavior of Au and Pt is discussed in detail in terms of defect formation volumes and migration thermodynamics.

Metastable Defects in Tritiated Amorphous Silicon

2007 ◽  
Vol 989 ◽  
Author(s):  
Tong Ju ◽  
Janica Whitaker ◽  
Stefan Zukotynski ◽  
Nazir Kherani ◽  
P. Craig Taylor ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Liquid Nitrogen ◽  
Beta Decay ◽  
Defect Density ◽  
Average Energy ◽  
Liquid Nitrogen Temperature ◽  
Beta Particle ◽  
Dangling Bond ◽  
Staebler Wronski Effect ◽  
Induced Defects

AbstractThe appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to 3He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half âlife of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 1016 to 1017 /cm3 , which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3x1019/cm3 after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2x1020/cm3). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200°C, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150°C, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.

An Alternative Model for the Kinetics of Light-Induced Defects in A-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
Paulo V. Santos ◽  
W. B. Jackson ◽  
R. A. Street
Keyword(s):  
Time Dependence ◽  
Valence Band ◽  
Defect Formation ◽  
Defect Density ◽  
Generation Rate ◽  
Band Tail ◽  
Defect Generation ◽  
Wide Range ◽  
Induced Defects ◽  
Kinetics Of

ABSTRACTThe kinetics of light-induced defect generation in a-Si:H was investigated over a wide range of illumination intensities and temperatures. The defect density around 1016cm-3 exhibits a power-law time dependence Ns ∼ G2εfε with ε = 0.2 to 0.3, where G is the photo-carrier generation rate. A model for the kinetics of defect generation is proposed based on the existence of an exponential distribution of defect formation energies in the amorphous network, associated with the valence band tail states. The model reproduces the observed time dependence of the defect density with an exponent e determined by the exponential width of the valence band tail. The temperature dependence of the defect generation rate is well-reproduced by the model, which provides a connection between the Stabler-Wronski effect and the weak-bond model.

Formation of Defects in MBE Re-Grown GaAs Films on GaAs/AlGaAs Heterostructures

2002 ◽  
Vol 744 ◽  
Author(s):  
M. Lamberti ◽  
V. Tokranov ◽  
R. Moore ◽  
M. Yakimov ◽  
A. Katsnelson ◽  
...  
Keyword(s):  
Focused Ion Beam ◽  
Defect Formation ◽  
Defect Density ◽  
Ion Beam ◽  
Stacking Faults ◽  
Tem Analysis ◽  
Planar Defects ◽  
Site Specific ◽  
Al Content ◽  
Gaas Films

ABSTRACTIn the present work, we examine the formation of defects on the sidewall slope in 1 μm - thick GaAs layers regrown on GaAs/AlGaAs heterostructures. Site-specific TEM specimens of sidewall slopes are obtained using focused ion beam combined with lift-out method. TEM analysis shows planar defects, such as stacking faults and microtwins, dislocations and large twinned areas, nucleating on the AlGaAs surfaces. SIMS and EDX reveal an increase in carbon and oxygen at the interface. The defect density increased with Al content exceeding 1010 cm-2 on Al0.4Ga0.6As. The defect formation is related to the oxidation of Al-containing surfaces.

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