bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Hydrogen Dilution on the Hot-Wire Deposition of Microcrystalline Silicon
Authors: Wanka H. N. , Zedlitz R. , Heintze M. , Schubert M. B. 
Published: April 2011

AbstractThe growth of amorphous (a-Si:H) and microcrystalline (pc-Si) silicon by hot-wire chemical vapor deposition (HWCVD) has been studied by combining in-situ ellipsometry, atomic force microscopy (AFM), and Raman spectroscopy. Generally a dense nucleation layer is formed during a-Si:H HWCVD, containing nuclei about 0.8 nm high and 10 to 20 nm in diameter. The surface roughness gradually increases with film thickness and settles at a root mean square (RMS) value of 1.6 nm at about 200 nm thickness. For hydrogen dilution at gas flow ratios x=[H2]/[SiH4] of 15 to 120 microcrystalline material was obtained. The grain size and nucleation layer, however, are strongly dependent on x. Low H2 dilution enhances the formation of an amorphous-like interface layer from which the μc-Si:H growth eventually starts. Increasing x promotes the etching of amorphous regions and the surface diffusion of precursors, resulting in larger nuclei. X = 30 yields extended μc-Si nuclei (30 nm height, 90 nm diameter) and a pronounced increase in surface roughness for thicker films, but suppresses the formation of the amorphous-like nucleation layer. A further increase in x remarkably lowers the growth rate, but smoother surfaces at comparable film thickness and larger lateral dimensions of the grains occur. This is interpreted as incipient etching of the crystallites.
On the Way Towards High Efficiency Thin Film Silicon Solar Cells by the “Micromorph” Concept
Authors: Meier J. , Torres P. , Platz R. , Dubail S. , Kroll U. , Selvan J. A. Anna , Vaucher N. Pellaton , Hof Ch. , Fischer D. , Keppner H. , Shah A. , Ufert K. -D. , Giannoulès P. , Koehler J 
Published: April 2011

AbstractRecently the authors have demonstrated that compensated or “midgap” intrinsic hydrogenated microcrystalline silicon (μc-Si:H), as deposited by the Very High Frequency Glow Discharge (VHF-GD) technique, can be used as active layer in p-i-n solar cells. Compared to amorphous silicon (a-Si:H), μc-Si:H was found to have a significantly lower energy bandgap of around 1 eV. The combination of both materials (two absorbers with different gap energies) leads to a “real” tandem cell structure, which was called the “micromorph” cell. Micromorph cells can make better use of the sun's spectrum in contrast to conventional double-stacked a-Si:H / a-Si:H tandems.The present study will show that the compensation technique (involving boron “microdoping”) used sofar for obtaining midgap μc-Si:H can be replaced by the application of a gas purifier. The use of this gas purifier has a beneficial influence on the transport properties of undoped intrinsic μc-Si:H. By this procedure, increased cell efficiencies in both, single microcrystalline silicon p-i-n as well as micromorph cells could be obtained. In the first case 7.7 % stable, and in the second case 13.1% initial efficiency could be achieved under AM1.5 conditions. Preliminary light-soaking experiments performed on the tandem cells indicate that microcrystalline silicon could contribute to an enhancement of the stable efficiency performance. Micromorph cell manufacturing is fully compatible to a-Si:H technology; however, its deposition rate is still too low. With further increase of the rate, a similar cost reduction potential like in a-Si:H technology can be extrapolated.
Effects of Deposition Power and Temperature on the Properties of Heavily Doped Microcrystalline Silicon Films
Authors: Miri A. M. , Chamberlain S. G. , Nathan A. 
Published: April 2011

AbstractWe studied the effect of RF deposition power and temperature on the electrical and structural properties of plasma enhanced chemical vapor deposited (PECVD), heavily doped microcrystalline silicon films (n+μC-Si:H). The film growth process was found to be CVDlike at low powers and PVD-like (Physical Vapor Deposition) at high powers. We show that the film properties strongly depend on the nature of the growth process. We observed that at low temperatures the microcrystalline formation is mainly governed by the presence of hydrogen. This can be improved by increasing the substrate temperature. However, a further increase in substrate temperature tends to reduce hydrogen incorporation into the film and hence decreases the role of hydrogen in the formation of microcrystallites. Resistivities as low as 0.1 Ω.cm were achieved for 500Å thin layers deposited at a relatively low temperature of 220°C and power density of 40mW/cm2.
On the Effect of Substrate Temperature on a-Si:H Deposition Using an Expanding Thermal Plasma
Authors: Severens R. J. , Sanden M. C. M. Van De , Verhoeven H. J. M. , Bastiaanssen J. , Schram D. C. 
Published: April 2011

AbstractFast (7 nm/s) deposition of amorphous hydrogenated silicon with a midgap density of states less than 1016 cm-3 and an Urbach energy of 50 meV has been achieved using a remote argon/hydrogen plasma. The plasma is generated in a dc thermal arc (0.5 bar, 5 kW) and expands into a low pressure chamber (20 Pa) thus creating a plasma jet with a typical flow velocity of 103 m/s. Pure silane is injected into the jet immediately after the nozzle, in a typical flow mixture of Ar:H2:SiH4=55:10:10 scc/s. As the electron temperature in the recombining plasma is low (typ. 0.3 eV), silane radicals are thought to be produced mainly by hydrogen abstraction.Material quality in terms of refractive index, conductivity, microstructure parameter and optical bandgap was found to increase monotonously with substrate temperature, even up to 350 °C; for practically all low growth rate deposition schemes an optimum around 250 °C is observed. It will be argued that this behavior is consistent with a simple kinetic model involving physisorption and hopping, growth on dangling bonds and thermal desorption of hydrogen.
Phase Separation by Rapid Thermal Annealing in Si-Sub-Oxides Andnitrides Formed by Plasma CVD
Authors: Banerjee A. , Lucovsky G. 
Published: April 2011

AbstractHydrogenated silicon suboxide and subnitride films were deposited by a remote plasma enhanced chemical-vapor deposition (RPECVD) process. Rapid thermal annealing (RTA) of these alloys eliminated all of the bonded hydrogen and formed a two phase system. The microstructure of the annealed films showed silicon crystallites (c-Si) surrounded by amorphous layers. The amorphous layers were identified as SiO2 and Si3N4 in the annealed suboxides and subnitrides, respectively. The as-deposited films showed band edge photoluminescence (PL); however, no PL was observed from the annealed films. This indicates that there was no significant suboxide or subnitride bonding in the amorphous layers at the metallurgically-sharp c-Si-SiO2 and c-Si-Si3N4 interfaces, respectively.
In situ Ellipsometric Studies of the growth of a-Si:H films Prepared by the Hot wire Deposition
Authors: Bauer S. , Dusane R. O. , Biehl R. , Schroder B. 
Published: April 2011

AbstractIn situ ellipsometric studies have been performed during the nucleation and growth of hydrogenated amorphous silicon (a-Si:H) films prepared by the hot wire chemical vapour deposition (HWCVD) method in order to understand the growth mechanism of these films. For a comparison with films deposited by plasma enhanced chemical vapour deposition (PECVD), the hot wire deposition was carried out under similar conditions and reactor geometry as for the PECVD process. It is observed from the kinetic ellipsometry measurements that low filament temperature (TFil) and low gas pressure favour the growth of more dense films, but at lower deposition rates. Moreover, for a given set of conditions an increase in substrate temperature (Ts) leads to a higher final value of the film density with a different growth behaviour in the initial stage. Thus, the filament temperature in the hot wire method seems to have a similar effect on the film density as the rf power has in the PECVD process, which has been observed earlier. Film density and surface roughness obtained from spectroscopic ellipsometry using a tetrahedron model which takes into account the effect of hydrogen on the dielectric function, is used to get information about the film microstructure. A correlation between this microstructure, the growth behaviour and the electronic properties as the defect density or the ambipolar diffusion length in the films is also reported.
Advances in the Characterization of Compositionally-graded Layers in Amorphous Semiconductor Solar Cells by Real Time Spectroellipsometry
Authors: Collins R. W. , Kim Sangbo , Koh Joohyun , Burnham J. S. , Jiao Lihong , Chen Ing-Shin , Wronski C. R. 
Published: April 2011

AbstractWe have developed a real time spectroellipsometry data analysis procedure that allows us to characterize compositionally- graded amorphous semiconductor alloy thin films prepared by plasma-enhanced chemical vapor deposition (PECVD). As an example, we have applied the analysis to obtain the depth-profile of the optical gap and alloy composition with ≤15 Å resolution for a hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx:H) film prepared by continuously varying the gas flow ratio z=[CH4]/{[CH4]+[SiH4]} in the PECVD process. The graded layer has been incorporated at the p/i interface of widegap a-Si1−xCx:H (x∼0.05) p-i-n solar cells, and consistent improvements in open-circuit voltage have been demonstrated. The importance of the graded-layer characterization is the ability to relate improvements in device performance directly to the physical properties of the interface layer, rather to the deposition parameters with which they were prepared.
Intermediate Layers in the A-Si:H Growth Processes
Authors: Aivazov A. A. , Bodyagin N. V. , Vikhrov S. P. 
Published: April 2011

AbstractThe intermediate layers (IL) exist at the boundary between liquid (plasma, gas) and solid phases during production processes of a-Si:H. The IL properties differ from the properties of the boundary regions anomaly. The substance in IL is in a strong nonequilibrium state of the bifurcation or the cascade of bifurcations. The processes in the IL determine the properties and the structure of the material being produced.
Optical Absorption in Amorphous Silicon
Authors: O'Leary S. K. , Zukotynski S. , Perz J. M. , Sidhu L. S. 
Published: April 2011

AbstractThe role that disorder plays in shaping the form of the optical absorption spectrum of hydrogenated amorphous silicon is investigated. Disorder leads to a redistribution of states, which both reduces the ‘Tauc’ gap and broadens the absorption tail. The observed relationship between the ‘Tauc’ gap and the breadth of the absorption tail is thus explained.
Temperature Dependence of the Photoconductivity and the Near Absence of Light-Induced Defects in a-SixGe1-x:H
Authors: Fritzsche H. , Stradins P. , Belomoin G. 
Published: April 2011

AbstractThe photoconductivities ap of glow discharge deposited a-Ge:H and amorphous Si-Ge alloys prepared in different laboratories were measured between 4.2K and 300K and compared with σp(T) of intrinsic and compensated a-Si:H films. The alloys as well as a-Ge:H do not exhibit thermal quenching of σp(T) at elevated temperatures which suggests that the valence and conduction band tails have similar widths. Remarkable is the near absence of light-induced metastable defects in the alloys as well as in a-Ge:H even after prolonged exposures at low temperatures.
Effects of Light Induced Degradation on the Distribution of Deep Defects in Hydrogenated Amorphous Silicon-Germanium Alloys.
Authors: Chen C. C. , Zhong F. , Cohen J. D. 
Published: April 2011

AbstractWe have characterized the defect state structure in a series of device quality glow discharge produced a-Si,Ge:H alloys with Ge content ranging from 30 at.% to 50 at.% using capacitance profiling, modulated photocurrent, transient junction photocurrent and photocapacitance measurements. As previously reported, these methods have allowed us to identify two types thermally induced defect transitions plus two types of optical transitions from deep defects. In the current study we have examined the changes in these defects, along with the changes in the hole mobility-time products, that result from prolonged light exposure. By comparing these changes in the annealed state and light soaked state of the same sample, we attempt to correlate the changes in defects with the hole mobility-time product. In general, although all of the defect bands are found to increase after light soaking, the relative factor is found to be different for the various defect transitions within the same sample. We also try to identify a defect bands may be acting as a “safe electron trap”, enhancing the lifetime of the minority carriers. We propose that the observed decrease of this defect band relative to the midgap defect band with light soaking could be a significant factor in determining the degradation of these a-Si, Ge:H alloys in the device performance.
Relaxation Measurements of the Persistent Photoconductivity in Sulfur-Doped a-Si:H.
Authors: Quicker D. , Kakalios J. 
Published: April 2011

AbstractThe slow relaxation of the persistent photoconductivity (PPC) effect in sulfur-doped hydrogenated amorphous silicon (a-Si:H) has been measured as a function of temperature and illumination time. The relaxation is found to be thermally activated, with an activation energy which varies with sulfur concentration, while illuminating the film for a longer time leads to a longer relaxation time. A correlation is observed between changes of the photoconductivity during illumination and the magnitude of the PPC effect following illumination. These effects are also observed in compensated a-Si:H, suggesting that the mechanism for the PPC effect is the same in both sulfur-doped a-Si:H and compensated a-Si:H. The presence of donor and compensating acceptor states in sulfur-doped a-Si:H could arise from valence alternation pair sulfur atom defects.
The Effect of Hydrogen Dilution Near The P/I Interface Region of A-Si:H P-I-N Solar Cells
Authors: Yeh C. N. , Han Daxing , Wang Qi , Xu Y. Q. 
Published: April 2011

AbstractIt is known that the a-Si:H solar cell with H-diluted i-layer (p-iH-n) exhibits a better stability under AMI light exposure than the non-diluted solar cell (p-i-n). Recently, Wang et al. found that the a-Si:H solar cell when inserting a thin H-diluted i-layer between the p- and the i-layer (p-iH-i-n) shows the same stability as a p-iH-n solar cell after 600 hours light soaking. It was suggested that the stabilization of a H-diluted a-Si:H solar cell is through controlling its p/i interface. In this work, we report the electroluminescence (EL) measurements of a-Si:H solar cells with p-iH-n, p-iH-i-n and p-i-n structures made in identical conditions except the difference in H-dilution processing. EL spectra in a wide range of temperature indicate that the defect-band emission can be controlled through a thin H-diluted i-layer near the p/i interface region, but the main-band emission depends more on the diluted i-layer thickness. According to the temperature dependence of the EL efficiency, the valence band-tail width of the active layer in the p-iH-i-n cell is estimated to be about 13% broader than that in the p-iH-n cell. From the total EL intensity as a function of the forward current density, the recombination processes at room temperature are suggested to be a monomolecular type for p-iH-wn, p-iH-i-n, and p-i-n structures.
Calorimetric Investigation of Relaxation Processes in Disordered Semiconductors
Authors: Budaguan B. G. , Aivazov A. A. , Sazonov A. Yu. 
Published: April 2011

AbstractThe comparative study of relaxation processes in amorphous hydrogenated (a- Si:H) and porous silicon (PS) by use of differential scanning calorimetry (DSC) measurements is presented. Films of a-Si:H were deposited by RF glow discharge of two gas mixtures (10% SiH4+ 90% H2) and (5% SiH4 + 95% He). PS films have been prepared by electrochemical etching of 1Ω-cm (p- PS) and of 0.01Ω-cm (p+ PS) ptype Si substrates. The DSC traces were recorded during the heating of samples at a constant rate of 10°C/min from 20 to 5700C in an Ar atmosphere. All investigated samples present a low temperature exothermic effect with a maxima within 120-2800C. At higher temperatures (T>3000C) a second exothermic effect is observed for a-Si:H films prepared from both hydrogen and helium diluted silane mixtures while two endothermic effects are observed for PS samples. Analysis of the low temperature exothermic effects has been performed, and focussed on the relaxation of weak Si-Si bonds which are the features of both amorphous hydrogenated and porous silicon. It was shown that the endothermic effect connected with hydrogen effusion from PS at higher temperatures is compensated by exothermic structural rearrangement in the case of a-Si:H.
1/f Noise and Thermal Equilibration Effects in Hot Wire Deposited Amorphous Silicon
Authors: Khera G. M. , Kakalios J. , Wang Q. , Iwaniczko E. 
Published: April 2011

AbstractMeasurements of the conductance fluctuations and thermal equilibration of the dark conductivity of a series of undoped hydrogenated amorphous silicon thin films synthesized by Hot-Wire Chemical Vapor Deposition (HWCVD), with hydrogen contents varying from less than one to twelve atomic percent are reported. The spectral density of the conductance fluctuations varies inversely with frequency f and is dependent upon hydrogen concentration; the 1/f noise statistics are non- Gaussian, indicating correlated fluctuators as is observed in PECVD a-Si:H. These results indicate that aspects of electronic transport and defect dynamics in HWCVD films are similar to those in PECVD a-Si:H films.
New Evidence for Deep Defect Relaxation in Hydrogenated Amorphous Silicon from Junction Capacitance Methods
Authors: Cohen J. David , Gardner Adam D. , Kwon Daewon 
Published: April 2011

AbstractWe have carried out capacitance transient measurements on lightly PH3 doped a-Si:H films incorporating both ohmic and blocking contacts. We find that the previously reported anomalous variation of emission time with filling pulse duration is completely independent of whether one uses an n+ c-Si substrate (providing a reasonably ohmic back contact) or a p+ c-Si substrate (giving a blocking back contact). Quite similar behavior is observed on a sample which includes an n+ a-Si:H layer at the back contact, exhibiting a variation of more than 2 orders of magnitude change in emission time when the filling pulse duration is decreased from Is to 100μs. Computer simulations are used to demonstrate that for a fixed (non-relaxing) deep state distribution, a filling problem in general cannot account for the observed experimental behavior. Finally, we report measurements that demonstrate that the filling of defects too close to the barrier interface can create difficulties observing the relaxation effects when an n+ a-Si:H contacting layer is used.
Photoconductivity of a-Si:H as a Function of Doping, Temperature and Photocarrier Generation Rates Between 1013 and 1028cm-3s-1
Authors: Stradins P. , Fritzsche H. , Kopidakis N. , Tzanetakis P. 
Published: April 2011

AbstractThe steady state photoconductivity up of n-type, p-type and intrinsic a-Si:H has been studied up to photocarrier generation rates of G=5×1027cm-3s-1. In the 20ppm B2H6/SiH4 p-type sample photoconduction switches from holes at low G to electrons at high G. The electron photoconduction at high G is increased by n-type and decreased by p-type doping. This is explained by the charge state of the dominant electron recombination centers. The σp(G) curves of doped and intrinsic a-Si:H merge at the highest G used.
Hall-Effect and Sign Properties in Hydrogenated Amorphous and Disordered Crystalline Silicon
Authors: Nebel C. E. , Rother M. , Summonte C. , Heintze M. , Stutzmann M. 
Published: April 2011

AbstractHall experiments on a series of microcrystalline, microcrystalline-amorphous, amorphous and crystalline silicon samples with varying defect densities are presented and discussed. Normal Hall effect signatures on boron and phosphorus doped hydrogenated amorphous silicon are detected. We interpret these results to be due to a small volume fraction of nanocrystalline Si, which falls below the detection limits of Raman experiments. Hydrogenated amorphous silicon, prepared under conditions far away from microcrystalline growth, shows the known double sign anomaly, Sign reversals in c-Si, where the disorder is increased by Si implantation up to very high levels, could not be detected.
High Deposition Rate a-Si:H for the Flat Panel Display Industry
Authors: Hautala J. , Saleh Z. , Westendorp J. F. M. , Meiling H. , Sherman S. , Wagner S. 
Published: April 2011

AbstractHigh deposition rates and good quality electrical properties and thickness uniformities over large areas are required for all three films (SiNx, a-Si:H and n+a-Si:H) composing the thin film transistors (TFTs) for the AMLCD industry, while maintaining high tool up-time and low particle formation. Generally these conditions have been achieved for most single-panel multichamber PECVD systems; however, it has become increasingly apparent that a compromise is drawn between the TFT mobility and the deposition rate of the a-Si:H layer. Thus it becomes essential to clearly assess the industry requirements for both deposition rates as well as TFT performance for the different device structures used for AMLCDs, and to discover and control these underlying material properties.The TEL VHF (40/60 MHz) PECVD system produces high quality, low defect density a- Si:H at deposition rates exceeding 1500 Å/min when analyzed by FTIR, CPM, photo and dark conductivity. Even though the low deposition rate a-Si:H exhibits very similar bulk properties, higher mobility TFTs are produced with a-Si:H deposited at lower RF power. Having both a high ion flux and low ion energy in the SiH4 discharge are likely the most critical conditions for controlling the a-Si:H quality and thus the TFT mobility. Increasing the RF frequency enhances both of these effects, as well as provides a higher deposition rate for a given power density and a higher power threshold for particle/powder formation. For these reasons it is likely a 40/60 MHz plasma will produce better performing TFTs for a given deposition rate when compared with a conventional 13.56 MIHz system. Other process conditions such as diluting the SiH4 in H2 or Ar also seem to play an important role in the optoelectronic properties of the a-Si:H film and ultimately the TFT performance.