The Origin of the Enhanced Optical Absorption in Hot Wire Microcrystalline Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
F. Diehl ◽  
B. Schröder ◽  
H. Oechsner
Keyword(s):  
Optical Absorption ◽  
Grain Boundary ◽  
Absorption Coefficient ◽  
Grain Boundaries ◽  
Structural Properties ◽  
Hydrogen Content ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Scattering Effects ◽  
Induced Changes

ABSTRACTThe phenomenon of enhanced optical absorption in hot wire microcrystalline silicon (hw-μ-Si:H) has been investigated with respect to the structural properties of the as deposited as well as annealed films. The influence of the structural properties on the absorption behavior is explained within the framework of a model. In this model the μc-Si:H is assumed to consist of crystalline grains surrounded by grain boundaries embedded into an amorphous matrix. Because of the relaxation of the k-selection rule the absorption is supposed to be higher for the disordered grain boundaries than for the crystalline grains. The absorption coefficient α is derived from the superposition of the absorption coefficients for the amorphous, crystalline and grain boundary regions weighted by their appropriate volume fractions. According to experimental results it is furthermore assumed that the absorption of the grain boundary regions correlates with the hydrogen content of the films. The model is proven and confirmed by crucial experiments especially concerning the influence of the hydrogen content on the absorption coefficient. Other possible reasons that might influence the enhanced optical absorption such as strain induced changes of α and light scattering effects are also discussed and explicitely excluded by appropriate experiments to be the essential enhancement reasons.

Light scattering and enhanced optical absorption in hot wire microcrystalline silicon

1998 ◽  
Vol 84 (6) ◽  
pp. 3416-3418 ◽  
Author(s):  
F. Diehl ◽  
B. Schröder ◽  
H. Oechsner
Keyword(s):  
Light Scattering ◽  
Optical Absorption ◽  
Hot Wire ◽  
Microcrystalline Silicon

Light-Induced Change of Si-H Bond Absorption in Hydrogenated Amorphous Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
Guozhen Yue ◽  
Liangfan Chen ◽  
Qi Wang ◽  
Eugene Iwaniczko ◽  
Guanglin Kong ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Hydrogenated Amorphous Silicon ◽  
Wave Number ◽  
Ir Absorption ◽  
Hot Wire ◽  
Induced Changes ◽  
Hydrogenated Amorphous

ABSTRACTDevice-quality a-Si:H films were prepared by glow discharge CVD with pure or H-diluted silane as well as by hot-wire CVD. The hydrogen content was varied from ∼2 to 15 at. %. The Si-H bond absorption and its light-soaking-induced changes were studied by IR and differential IR absorption spectroscopes. The results indicate that the more stable sample exhibits an increase of the absorption at wave number ∼2000 cm−1, and the less stable one exhibits a decrease at ∼2040 cm−1and an increase at ∼1880 cm−1.

Identification of Possible Bonding Sites for Post Deposition Oxygen Absorption in Microcrystalline Silicon

2004 ◽  
Vol 808 ◽  
Author(s):  
L. M. Gedvilas ◽  
A. H. Mahan
Keyword(s):  
Grain Boundaries ◽  
Surface Region ◽  
Oxygen Absorption ◽  
Hot Wire ◽  
X Ray Diffraction ◽  
Microcrystalline Silicon ◽  
X Ray ◽  
Crystallite Surface ◽  
Si Films ◽  
Post Deposition

ABSTRACTUsing infrared (IR) spectroscopy and x-ray diffraction, the nature of the grain boundaries in twom c-Si films deposited by hot wire CVD, displaying similar crystalline volume fractionsbut very different behavior upon exposure to atmospheric contaminants, is analyzed. For the film exhibiting significant post deposition oxidation, the IR spectrum in the 2100 cm−1 Si-H stretch mode region contains two sharp and very narrow peaks, suggesting that the crystallites have been incorporated into them c-Si films with their hydrogenated surfaces relatively intact.By comparing these peak frequencies to those in the literature for Si-H bonding on c-Si surfaces, we identify certain crystallite orientations which, when comprising the c-Si grain boundaries, are particularly susceptible to oxidation. We further suggest that the distribution of H in this grain boundary/crystallite surface region is crucial for depositing c-Si films with good electronic properties and minimal post deposition oxidation.

Defects in Microcrystalline Silicon Prepared With Hot Wire CVD

2002 ◽  
Vol 715 ◽  
Author(s):  
F. Finger ◽  
S. Klein ◽  
T. Dylla ◽  
A. L. Baia Neto ◽  
O. Vetterl ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Thin Film Solar Cells ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Grain Sizes ◽  
Preparation Conditions ◽  
Hydrogen Dilution ◽  
Process Gas

AbstractThe influence of the preparation conditions in hot wire chemical vapour deposition (HWCVD) on the electronic properties of microcrystalline silicon is investigated in view of application of the material in thin film solar cells. Poor grain boundary passivation, as a result of hydrogen etching at strong hydrogen dilution of the process gas or thermal desorption of hydrogen at high deposition temperatures, is considered a main obstacle for material optimisation. We conclude that optimum μc-Si:H solar cell material, both from HW-CVD and from plasma enhanced CVD, is not necessarily obtained with largest grain sizes and apparent highest crystalline content, but rather by a material prepared under conditions which yield a compact morphology with an effective grain boundary passivation.

scholarly journals Temperature dependence of the optical absorption coefficient of microcrystalline silicon

2004 ◽  
Vol 338-340 ◽  
pp. 222-227 ◽  
Author(s):  
A. Poruba ◽  
J. Springer ◽  
L. Mullerova ◽  
A. Beitlerova ◽  
M. Vaněček ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Absorption Coefficient ◽  
Temperature Dependence ◽  
Optical Absorption Coefficient ◽  
Microcrystalline Silicon

An Absorption Study of Microcrystalline Silicon Deposited by Hot-Wire CVD

1997 ◽  
Vol 467 ◽  
Author(s):  
F. Diehl ◽  
W. Herbst ◽  
B. Schröder ◽  
H. Oechsner
Keyword(s):  
Optical Absorption ◽  
Crystallite Size ◽  
Gas Pressure ◽  
Absorption Enhancement ◽  
Flow Ratio ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Filament Temperature ◽  
Enhanced Absorption ◽  
Hydrogen Dilution

ABSTRACTThe effect of variation of the preparation parameters filament temperature Tfil, gas pressure p and hydrogen dilution (H2/SiH4-flow ratio) on the absorption spectra of microcrystalline silicon deposited by the hot-wire technique (hw-μc-Si:H) has been studied by means of Photothermal Deflection Spectroscopy (PDS). We find an enhanced absorption of the μc-Si:H compared to crystalline silicon in the band gap (defect absorption) as well as in the interband transition region. An increase of absorption has already been reported for μc-Si:H films prepared by different techniques. In the case of hw-pc-Si:H we observe a relation between the absorption enhancement and the crystallite size. Increasing the gas pressure from 35 to 400 mTorr (Tfil=1850°C) or the filament temperature from 1750°C to 1950°C (p=100mTorr) the crystallite sizes, deduced from X-ray diffraction measuements, range from 10 to 60 nm. An alteration of the hydrogen dilution by varying the flow ratio between 2.5 and 25 does not affect the crystallite size and the optical absorption remains constant. In our opinion the enhancement cannot be described by a simple superposition of an amorphous and a crystalline absorption coefficient weighted by the volume fractions of the amorphous and crystalline phase, respectively. The possible reasons for the enhanced absorption will be discussed. The variation of the crystallite size with deposition conditions offers the possibility to control the optical absorption of μc-Si:H which is important for incorporating the material either as window layers or intrinsic layers in solar cells.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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