bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shock Induced Energetic Phase Transformations
Authors: Bardo Richard D. , Agassi Dan 
Published: April 2011

AbstractUltrafine diamond dust and the metastable fullerenes C60 and B24N36 offer new pathways of energy release which are unattainable in conventional energetic materials. Theoretical and experimental studies indicate that the high bare-surface strain energies of these small particles are released in rapid (< 1 μsec) phase changes. For diamond, C60 and B24N36, strain energies of 1000, 1210 and 1245 cal/g, respectively, may be released during transition to graphite, diamond and hexagonal BN under pressures exceeding 100 kbar. It is shown that the behavior of these nanoscale particles under high shocks may be traced to their intrinsic five-fold and icosahedral symmetry, which leads to an incompatibility of global and local driving forces for space filling under high compression. From a correlation function analysis, it is shown that shear can induce long range correlations of fluctuations which arise from geometrical frustration, thereby reducing the activation energy for phase change. For the first time, critical stresses and symmetry rules are determined for such phase changes in aggregates of nanoscale particles.
Laser Interference Structuring of a-Si:H
Authors: Nebel C. E. 
Published: April 2011

AbstractLaser interference structuring with a pulsed Nd:YAG laser set-up is introduced and typical geometric dimensions and limitations are discussed. Intensity modulated laser beams are used to recrystallize amorphous silicon layers periodically at the intensity maxima. Stripe or tip structures of multi-crystalline (mc) silicon with sub-micrometer dimensions are shown. Structural, electronic and optical properties of the mc-Si structures are discussed. A hybrid thin film p-i-n solar cell architecture is described where the textured TCO is replaced by a flat TCO and a laterally structured boron doped mc-Si window layer. Light trapping, light diffraction and higher internal electric fields are proposed to be the main advantages of such a solar cell.
Efficiency Improvement of a-Si Solar Cells Deposited in a Single Chamber, Large Area, Pecvd Reactor
Authors: Terzini E. , Privato C. , Avagliano S. , Mangiapane P. , Fasolino T. 
Published: April 2011

AbstractIn order to realize large area integrated a-Si modules using a commercial, single chamber, PECVD reactor, an accurate optimization of deposition process for p-i-n solar cell has been performed leading to a 1 cm2 device efficiency value of 10.3 %.Besides the efficiency improvements achieved by the insertion of a graded layer at p/i interface and by the introduction of SnO2 Asahi type U substrate, an “interface cleaning procedure”, based on NF3 flushing step, was the key for the cells Voc and fill factor increase.Microcrystalline n+ layer, ZnO/Ag back contact and device thermal annealing gave further contributions to the cell efficiency.Utilizing this technology, a large area p-i-n modules (900 cm2) with an initial efficiency of 8.5% has been manufactured.
Examination of 1-D Position Sensitive Detector Performance Through Analysis of Front Contact Heterojunction
Authors: Topiˇ M. , Smole F. , Furlan J. , Fortunato E. , Martins R. 
Published: April 2011

AbstractThe influence of different TCOs (SnO2 and ITO) on the photoelectrical properties of 1 -D position sensitive detectors based on p-i-n structures was studied. A strong cross-contamination in the p-layer and contamination in the i-layer reduce the quality of the device. Numerical analysis of TCO/p-i-n structure also revealed a strong increase in defect states at the p-layer surface which can be attributed to the reduction of TCO. ITO seems to be less appropriate for a front TCO, although the spectral response of the p-i-n structure under reverse bias is not significantly affected by the conditions at the TCO/p heterojunction.
Light-Induced Degradation of Amorphous Silicon-Germanium Alloy Solar Cells Deposited at High Rates
Authors: Sugiyama S. , Xu X. , Yang J. , Guha S. 
Published: April 2011

AbstractWe have studied the light-induced degradation of amorphous silicon-germanium (a-SiGe:H) alloy single-junction solar cells with high initial performance deposited at high rates. The intrinsic layers were deposited using microwave (MW) glow-discharge technique at deposition rates between 10 and 40 Å/s. The results show that light-induced degradation of the cells is higher than that of cells deposited at low rates using RF glow-discharge technique, and it does not strongly depend on deposition rates over this range. The total hydrogen content and the ratio of Si-H2, Ge-H, and Ge-H2 to Si-H bonding estimated by infrared (IR) absorption in films are correlated with the cell degradation results. We have also investigated the effect of ionbombardment on film properties. Films with low ion-bombardment are more porous and have higher composition of Si-H2 and Ge-H2 bonding. Appropriate ion-bombardment makes denser structure in a-SiGe:H alloy films deposited at high rates. This improves the cell performance as well.
Analytical model of a-Si/c-Si Hit Solar Cell
Authors: Furlan J. , Popović P. , Smole F. , Topič M. 
Published: April 2011

AbstractUsing suitable simplifying approximations inside the particular regions of a p-i a-Si/n c-Si heterojunction solar cell, the analytical expressions for the solar cell current-voltage characteristics are derived showing clearly the dominating first-order effects on solar cell performance. The derived closed form solutions indicate that in the useful forward voltage range the largest dark current component of this cell is the interface recombination current and that the main contribution to the photocurrent comes from the light generated holes in the c-Si substrate layer. The transfer of holes across the intrinsic layer and over the ΔEv barrier is strongly suppressed resulting in an attenuation of solar cell dark and photocurrent.
Analysis of the Conduction Properties of a-Si:H n+-i-n+ Structures Via Accurate Computer Modelling
Authors: Chatterjee P. , Vanderhaghen R. , Equer B. 
Published: April 2011

AbstractAnalysis of the current density-voltage (J-V) characteristics of sandwich a-Si:H n+-i-n+ structures made of the same materials but with varying thicknesses of the i-layer, has given rise to two somewhat contradictory speculations regarding the density of states (DOS) at the Fermi level of the i-layer. The first of these postulates that the DOS over the first 2000–4000A of the i-a-Si:H layer is larger by a factor of 3–10 than that in the rest of the film With this hypothesis however, the experimentally observed low activation energies (Ea) for thin n+-i-n+ devices remain unexplained. In the other analysis, a consideration of the n+-i space-charge regions enables a fair description of the experimental results assuming that the electron DOS is position independent in the i-layer. In the present report we use accurate computer modelling to calculate and analyse the J-V characteristics of a-Si:H n+-i-n+ structures in the low bias ohmic region as a function of device thickness, ambient temperature and the quality of the i-layer. We find that the n+-i interface is abrupt only for a device with a high dangling bond density. For good quality material however, the depletion width extends right across the i-layer for a thin device and the zone of charge neutrality is never reached, resulting in low values of Ea in the ohmic region. In the latter case Ea increases with i-layer thickness. Analysis by detailed computer modelling confirms that the experimental results may be explained by assuming a density of states independent of the thickness of the i-layer.
Thin p-type Microcrystalline Silicon Film on Various Substrates
Authors: Rath J. K. , Wallinga J. , Schropp R. E. I. 
Published: April 2011

AbstractThin(<20nm) p-type microcrystalline silicon f'dms have been deposited by PECVD in an unusual parameter regime, specifically optimized for extremely thin films. High conductivity (>10.2 Scm−1) and low activation energy(<0.08eV) of thin films have been achieved on various metal oxide substrates i.e., Coming 7059 glass, SnO2:F, TiO2 and Ta2O5. Crystallinity was confirmed by Raman spectroscopy and UV reflectance. Deposition of p-μc-Si:H is possible on void rich films (a-SiC:H and low temperature deposited a-Si:H) but not on device quality a-Si:H. Cells made in a superstrate structure using p-μc-Si:H as the window layer directly on top of SnO2:F coated glass yielded 9.63% efficiency, with an improvement in the blue spectral response compared to the cell made with a- SiC:H(B) as window layer. Tandem cells (a-Si:H/a-Si:H) incorporating p-μc-Si:H along with n-μc- Si:H in the tunnel junction yielded 8.8% efficiency.
Low Temperature Hydrogen Induced Amorphous to Crystalline Silicon Phase Transformations
Authors: Fortmann C. M. , Hapke P. , Lambertz A. , Finger F. 
Published: April 2011

AbstractThe low temperature hydrogen induced phase transformations are the basis for the layer-by-layer micro-crystalline silicon growth technique which involves the sequential deposition of thin amorphous silicon layers followed by hydrogen treatment. Very high frequency-PECVD layer-by-layer microcrystalline film growth was studied as a function of frequency. The highest crystalline content films were prepared on glass substrates at 49.7 MHz with deposition cycle times of 12 seconds and hydrogen treatment times of 120 seconds or longer. At lower frequencies, 13.56 and 27 MHz, no micro-crystalline content was observed. At higher frequencies (94.7 MHz) crystalline content was reduced compared to that of the 49.7 MHz case. Crystalline content is not correlated with the hydrogen etch rate as the highest etch rates occurred at 94.7 MHz while etch rates at 49.7 and 27 MHz were lower. It is possible to prepare thin micro-crystalline films using the VHF layer-by-layer growth technique.
Recrystallisation of Preamorphized Silicon Investigated by RBS and PAC
Authors: Rohrlack G. , Freitag K. , Vianden R. , Gwilliam R. , Sealy B. J. , Jafri Z. 
Published: April 2011

AbstractThe technique of preamorphization is a well-known method to avoid channeling tails of implanted dopants when fabricating devices. This is achieved by implanting a nondopant atom to produce the amorphous layer. We studied the recrystallisation of silicon preamorphized by Si, Ge and Sn implants. The recrystallisation was investigated by RBS and the y-y perturbed angular correlation (PAC) technique. RBS provides information about the thickness and the perfection of the recovered layer. Additional experimental data are supplied by the PAC technique, which used the postimplanted radioactive isotope 111Ina s a probe atom. The recovery of the lattice structure in the vicinity of the probe atoms is monitored on a microscopic scale via the electric field gradient produced at the site of the In nucleus by the surrounding lattice defects. The results are discussed and compared to the RBS data.
Modified Triode Plasma Configuration Allowing Precise Control of Ion-Energy for Preparing High Mobility a-Si:H
Authors: Ganguly G. , Ikeda T. , Sakata I. , Matsuda A. 
Published: April 2011

AbstractWe have previously shown that the carrier drift mobility in amorphous silicon can be enhanced by optimizing the ion-bombardment energy during growth on conducting substrates. However, there exists a lack of reproducibility of samples exhibiting high mobility which we attribute to the rf field induced fluctuation of the plasma potential in a conventional (Te ≈ 2eV) silane plasma. Here we introduce an enclosed plasma configuration that allows us to confine the effect of the rf field and therefore obtain a low-electron-temperature (Te ≈ 0.1 eV) silane plasma as determined from Langmuir probe measurements. The measured ion-energy distributions correlate with those for electrons and the mean ion-energy can be controlled by biasing the substrate which allows us to reproducibly fabricate high drift mobility amorphous silicon.
A-Si:H Films Deposited by Dc-Masd Technique at High Substrate Temperature
Authors: Golikova O. A. , Kuznetsov A. N. , Kudojarova V. Kh. , Kazanin M. M. , Ikosarev A. 
Published: April 2011

AbstractDc-magnetron assisted silane decomposition technique has been tested for deposition of undoped a-Si:H at substrate temperature Ts=300–400°C. In the optimized conditions device-quality a-Si: H films were deposited independently of Ts. A low hydrogen content CH (up to 2 at.°) and microstructure variations are characteristic of the MASD films.
Saddle-Field Glow-Discharge Deposition of Amorphous Semiconductors
Authors: Gaspari F. , Sidhu L. S. , O'leary S. K. , Zukotynski S. 
Published: April 2011

AbstractWe present a dc saddle-field glow-discharge deposition procedure which combines the positive attributes of the conventional dc and rf glow-discharge techniques. Preliminary mass spectra analyses of both silane and methane glow-discharges demonstrates that ions constitute a significant fraction of the species reaching the film surface. Growth rate analyses suggest that ions play a significant role in the saddle-field glow-discharge deposition of amorphous semiconducting films.
Light-induced Stability of Layered Amorphous Hydrogenated Silicon Grown with Alternating Substrate Temperature
Authors: Yoona Jong-Hwan , Lee Czang-Ho 
Published: April 2011

AbstractWe present the results of studies on the light-induced stability of undoped layered hydrogenated amorphous silicon films grown with alternating substrate temperature between optimal and non optimal temperatures for device-quality films. Compared to the single layer films grown at optimal substrate temperature, the layered films show improved stability in the lightinduced state. Under intense light illumination of 3 W/cm2, the steady-state defect density of the layered film reached a saturation of 2×1016 cm−3, while the single layer film saturates at about 6×1016 cm−3. It is found that in the completely degraded state the photoconductivity in the layered film is also improved by a factor of two compared to the single layer film.
Properties of Substrate-Type a-Sihh Devices Prepared Using ECR Conditions
Authors: Dalal Vikram L. , Kaushal Sanjeev , Girvan Robert , Sipahi Levent , Hariasra Swati 
Published: April 2011

AbstractWe report on the preparation and properties of a-Si:H devices prepared at high temperatures on stainless steel substrates using low pressure ECR plasma deposition techniques. The devices were prepared using either Hydrogen or Helium as the plasma diluent gas. The use of He as the plasma gas led to films having significantly lower H concentration(4–5%) and a lower bandgap than comparable films made using hydrogen dilution. We find that we can make excellent devices, with good fill factors(over 70%) and voltages(over 0.86 V) using either H or He dilution. The use of He led to devices having smaller bandgap, by about 35–40 meV compared to devices made using H dilution. Detailed quantum efficiency measurements show that the hole collection in both types of devices is excellent, and that Urbach energies of tail states in each case is in the range of 43–45 meV.
Inert Gas Dilution and Ion Bombardment Effects in Room Temperature (35°C) Plasma Deposition of a-Si:H
Authors: Srinivasan Easwar , Lloyd Daniel A. , Fang Ming , Parsons Gregory N. 
Published: April 2011

AbstractPlasma enhanced chemical vapor deposition (PECVD) of a-Si:H with silane or silane and hydrogen at temperatures lower than 200°C commonly results in films with significant dihydride bonding and a high defect density. In this paper, we demonstrate the formation of monohydride dominant a-Si:H films using rf parallel plate PECVD at 35°C at deposition rates greater than 100 Å/min. In the as-deposited state, these films have low dark conductivity (∼10−9 S/cm) and low photoconductivity. Annealing the films at 150°C caused the monohydride dominant films to show photo to dark conductivity ratio near 105. Our results also indicate that an increase in monohydride fraction is not linked with a decrease in deposition rate.
Modulation of Growing Surface with Atomic Hydrogen and Excited Argon to Fabricate Narrow Gap a-Si:H
Authors: Futako W. , Shimizu I. , Fortmann C. M. 
Published: April 2011

AbstractHydrogenated amorphous silicon (a-Si:H) with a gaps narrower than 1.7 eV were made by repeating the deposition of a thin layer (1–3 nm thick) and the treatment of growing surface with a mixture of H and Ar*. Crystallization induced by permeation of hydrogen into the subsurface at high substrate temperature (>200C) was efficiently prevented by treating with a mixture of H and Ar*. The activation of growing surface may arise from releasing a part of hydrogen on surface by treating with Ar*. High quality a-Si:H films containing hydrogen of 3 atom % with a gap of 1.6 eV were made by chemical annealing with a mixture of H and Ar*.
In Situ Investigation of the a-Si:H/C-Si Interface
Authors: Feist H. , Swiatkowski C. , Elmiger J. R. , Zipfel M. , Kunst M. 
Published: April 2011

AbstractThe deposition of a-Si:H films on crystalline silicon substrates was monitored in situ by transient photoconductivity measurements in the microwave frequency range. At the start of the deposition a drastic increase of the interface recombination velocity was observed, followed by a rapid decrease. The implications of these results for the structure of the interface are discussed. Changes of the interface after deposition were detected without a change of the temperature, even at 250'C: The long relaxation time of the structure of the interface will be discussed. Ex situ results on the samples produced will be compared to the in situ results in view of the passivation properties of a-Si:H films on c-Si substrates.
Nuclear Magnetic Resonance Studies of Hydrogen in Amorphous Silicon
Authors: Norberg R. E. , Fedders P. A. , Leopold D. J. 
Published: April 2011

AbstractProton and deuteron NMR in hydrogenated amorphous silicon yield quantitative measures of species-specific structural configurations and their dynamics. Populations of silicon-bonded and molecular hydrogens correlate with photovoltaic quality, doping, illumination/dark anneal sequences, and with infrared and other characterizations. High quality films contain substantial populations of nanovoid-trapped molecular hydrogen.
1H Nmr in μc-Si:H Deposited With Different Plasma Excitation Frequencies and Silane Concentrations
Authors: Hari P. , Taylor P. C. , Finger F. 
Published: April 2011

AbstractSix samples of pc-Si:H were prepared by PECVD at 200°C with plasma excitation frequencies ranging from 13 MHz to 95 MHz. Four samples were prepared with gas mixtures of 3% SiH 4 in H2. For these samples the plasma excitation frequencies ranged from 13 MHz to 95 MHz. Two samples at a plasma excitation frequency of 95 MHz were prepared at 5% and 8% SiH4 in H2. All samples were deposited on aluminum foil and etched off using dilute HCI to form powdered samples. These samples were studied by nuclear magnetic resonance (NMR), electron spin resonance (ESR) and infrared (IR) absorption measurements. The broad and narrow components of the free induction decay (FID) in the NMR measurements were compared to the respective components that occur in a-Si:H. The broad components in the various samples of μc-Si:H are similar in width to the broad component in a-Si:H, but the narrow component is narrower by a factor of two as compared to the narrow components in μ-Si:H. The narrow component in pic-Si:H samples exhibits a beat pattern similar to a previously observed Pake doublet. ESR measurements performed between 20 K and 300 K show that the spin densities, which can be attributed to silicon dangling bond states, increase as a function of plasma excitation frequency. The hydrogen content of each μc-Si:H sample was estimated from the NMR measurements, and these estimates are in good arrangement with the hydrogen content estimated from IR measurements.
H2-Dilution vs. Buffer Layers for Increased Voc
Authors: Platz R. , Fischer D. , Hof C. , Dubail S. , Meier J. , Kroll U. , Shah A. 
Published: April 2011

AbstractHydrogen dilution and buffer layers, as two ways to obtain higher Voc values in a-Si:H p-i-n solar cells, are directly compared in the present study. Special emphasis is laid on stability against light soaking. H2-dilution in combination with lower substrate temperature yields higher Voc values and better stability as compared to buffer layers. However, light absorption is decreased due to the increased gap in H2-diluted cells. The stability of buffer layer cells can remarkably be ameliorated by boron doping and H2-dilution of the a-SiC:H buffer layer. However, stabilized efficiency is higher for optimized diluted cells than for cells with a buffer layer. An a-Si/a-Si stacked cell with a graded dilution for both cells yielded 10% initial efficiency with 17% relative degradation. Diluted a-Si:H cells at lower temperature become specially interesting in combination with a microcrystalline bottom cell. For such a “micromorph” tandem cell we obtained 11.4% initial efficiency.
Photocreated Defects and Light-Induced ESR in a-Si:H and Related Alloy Films
Authors: Shimizu Tatsuo , Durny Rudolf , Kumeda Minoru 
Published: April 2011

AbstractTwo major problems in the field of a-Si:H and related alloy films such as a-Sil-xNx:H are addressed in this contribution, namely, the photocreation of neutral Si dangling bonds and the origin of the components of the light-induced ESR (LESR). We have proposed a new model for the photocreation of neutral Si dangling bonds in a-Si:H based on the presence of floating bonds. The model can explain the metastabilization of the broken weak bonds without the movement of H atoms. The broad, the narrow, and the dangling bond components of the LESR signal have been attributed to holes captured at negatively charged floating bonds, electrons trapped at antibonding states of weak bonds and photoexcited carriers captured at charged dangling bonds, respectively.
Defect Characterization of High-Rate Deposited Hydrogenated Amorphous Silicon Films
Authors: Chan Florence Y. M. , Lam Y. W. , Chan Y. C. , Lin S. H. , Lin X. Y. , Lau W. S. , Chua S. J. 
Published: April 2011

AbstractHigh rate deposition of a-Si:H films has become one of the key techniques for low-cost, large-scale production of thin film devices. Hydrogenated amorphous silicon films were fabricated with a thermocatalytic PCVD method of which the deposition rate was up to 1.5 nm/sec. The Heterojunction Monitored Capacitance method was employed to determine the midgap-state densities in the undoped semiconductor film from high frequency C-V characteristics. Experimental results showed that the thermocatalytic PCVD method is an effective way to produce high-rate deposited a-Si:H films.
Dependence of Light-Induced Esr on NitroGen Content in Amorphous Silicon-Nitrogen Alloys
Authors: Zhang Jinyan , Ohtsuka Toshihiro , Kumeda Minoru , Shimizu Tatsuo 
Published: April 2011

AbstractThe LESR signals are observed for the a-Si1-xNx:H samples over a wide range of nitrogen content at 77K. By decomposing the LESR signals using three components, i.e. the neutral Si dangling bond (Do) component, the broad component with a linewidth of 16 G, and the narrow component with a linewidth of 5 G, we find that the three components are observed only in the Si-rich samples. The density of light-induced Do increases with x, whereas the densities of both the narrow and the broad components increase in the range of x≦0.32 and are almost independent of x for larger x. The g-value of the broad components falls down sharply from 2.01 to 2.006 with an increase in x, while the g-value of the narrow component is unchanged and it is around 2.004. All of the three components can be annihilated by sub-gap illumination. The origins of the broad and the narrow components are discussed.