Showing papers on "Amorphous silicon published in 1979"

Amorphous-silicon field-effect device and possible application

Abstract: The characteristics of an insulated-gate field-effect transistor made from amorphous silicon (a-Si) deposited in a glow discharge are discussed. It is suggested that the a-Si device could be applied with advantage in an addressable matrix of a liquid-crystal display panel.

Picosecond laser‐induced melting and resolidification morphology on Si

Abstract: Ultrafast melting and resolidification on the surface of a silicon crystal has been induced by picosecond laser pulses at 532 and 266 nm Optical microscopy and electron diffraction revealed the formation of amorphous silicon Details of surface morphology are sensitive functions of pulse intensity, energy, wavelength, and crystallographic orientation

Crystallographic orientation of silicon on an amorphous substrate using an artificial surface‐relief grating and laser crystallization

Abstract: Uniform crystallographic orientation of silicon films, 500 nm thick, has been achieved on amorphous fused‐silica substrates by laser crystallization of amorphous silicon deposited over surface‐relief gratings etched into the substrates. The gratings had a square‐wave cross section with a 3.8‐μm spatial period and a 100‐nm depth. The 〈100〉 directions in the silicon were parallel to the grating and perpendicular to the substrate plane. We propose that orientation of overlayer films induced by artificial surface patterns be called graphoepitaxy.

Microstructure of plasma‐deposited a‐Si : H films

Abstract: Using transmission and scanning electron microscopy, it is shown that plasma deposition of amorphous silicon hydrogen films from silane or silane/argon mixtures proceeds via nucleation and growth of islands of average lateral dimensions ∼100 A. If these islands do not coalesce into a homogeneous film, subsequent growth produces columnar morphology with low‐density interstitial regions. There is a strong correlation between the columnar structure and the presence of nonradiative recombination centers.

Crystallization in amorphous silicon

Abstract: Crystallization has been studied in amorphous silicon layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow one to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.

Recrystallization of implanted amorphous silicon layers. I. Electrical properties of silicon implanted with BF+2 or Si++B+

Abstract: Electrical properties of recrystallized amorphous silicon layers, formed by BF+2 implants or Si++B+ implants, have been studied by differential resistivity and Hall‐effect measurements. Electrical carrier distribution profiles show that boron atoms inside the amorphized Si layers can be fully activated during recrystallization at 550 °C. The mobility is also recovered. However, the tail of the B distribution, located inside a damaged region near the original amorphous‐crystalline interface, remains inactive. This inactive tail has been observed for all samples implanted with BF+2. Only in a thicker amorphous layer, formed for example by Si+ predamage implants, can the entire B profile be activated. The etch rate of amorphous silicon in HF and the effect of fluorine on the recrystallization rate are also reported.

a‐Si : H produced by high‐temperature thermal decomposition of silane

Abstract: Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.

Amorphous silicon as a passivant for crystalline silicon

Abstract: Hydrogenated amorphous silicon deposited on a p‐n junction in crystalline silicon causes a two‐order‐of‐magnitude reduction in leakage current compared to the performance of a state‐of‐the‐art thermal oxide passivant.

Electronic density of states in discharge‐produced amorphous silicon

Abstract: The localized state density distribution in the mobility gap of glow‐discharge amorphous silicon has been determined from capacitance‐voltage characteristics for metal/oxide/amorphous silicon (MOS) structures. This new method provides a smooth distribution of localized states throughout the mobility gap. The density of states increases from a minimum of the order of 1016 cm−3 eV−1 near midgap to more than 1018–1019 cm−3 eV−1 within 0.2 eV of the band edges.

Method for depositing silicon films and related materials by a glow discharge in a disiland or higher order silane gas

Abstract: Disilane (Si2 H6), trisilane (Si3 H8) or a higher order silane is applied in a glow discharge process to rapidly and efficiently form a film of hydrogenated amorphous silicon on a substrate. An inductively coupled RF glow discharge apparatus, a capacitively coupled glow discharge apparatus or a DC glow discharge apparatus may be employed to deposit the amorphous silicon on a conducting or non-conducting substrate. The disilane or higher order silanes may also be combined in a glow discharge process with gases which contain elements such as nitrogen or oxygen to rapidly deposit corresponding compound films.

Hydrogen content and density of plasma‐deposited amorphous silicon‐hydrogen

Abstract: The hydrogen concentration and density of amorphous semiconducting films prepared by glow‐discharge decomposition of silane have been measured as a function of deposition temperature. An inductively coupled as well as a capacitively coupled plasma‐decomposition system was used. For samples prepared by the capacitively coupled system, the hydrogen content decreased from 26 to 8 at.% and the density increased from 1.9 to 2.27 g/cm3 as the substrate temperature was increased from 25 to 450 °C.

Recrystallization of implanted amorphous silicon layers. II. Migration of fluorine in BF + 2 -implanted silicon

Abstract: Fluorine distribution profiles for silicon implanted with BF+2 have been measured by SIMS as a function of anneal temperature and time. Anomalous migration of fluorine is observed in samples having amorphized layers after implantation. Outdiffusion of fluorine occurs during recrystallization of the amorphous layer, and fluorine collects in regions of residual damage during annealing. This gettering of fluorine by defects illustrates the residual damage below the amorphized layer in samples implanted at room temperature is more difficult to anneal out than that in samples implanted at lower temperture (∼−110 °C).

Calculated temperature distribution during laser annealing in silicon and cadmium telluride

Abstract: By solving the time-dependent heat flow equation, the temperature reached by silicon and cadmium telluride surface layers under high power density ruby laser pulsed illumination, is calculated. The results are presented in directly useful figures allowing the determination of the surface temperature, its evolution towards the bulk as a function of time... In particular, it should be noticed that for a 25 ns half-power width, pulses of 0.8J/cm2 are sufficient to melt the top of an amorphous silicon layer, this value becomes noticeably lower for cadmium telluride.

Photoemission studies on in situ prepared hydrogenated amorphous silicon films

Abstract: Photoemission studies involving the valence and core levels of doped and undoped amorphous hydrogenated silicon (a-Si: H) prepared by the glow-discharge method are reported The valence-band spectra show states identified as hydrogen ls/silicon 3p—3s bonding orbitals which are sensitive to the bonding configuration of hydrogen Singly and multiply bonded hydrogen have been distinguished unambiguously A recession of the valence-band edge (E v) of up to 1 eV is observed for the highest hydrogen concentrations (∼50%) The amounts of boron and phosphorus incorporated into a-Si: H as dopants have been estimated through the corresponding core-level intensities The incorporation efficiencies are 80% (P) and 70% (B) respectively However, only 10% of the incorporated atoms act as dopants The position of the Fermi level relative to E v as a function of dopant concentration has also been determined By combining these positions with activation energies obtained from conductivity measurements, the locati

A new type of amorphous silicon photovoltaic cell generating more than 2.0 V

Abstract: A new type of plasma‐deposited amorphous silicon photovoltaic cell having a horizontally multilayered p‐i‐n unit‐cell structure has been developed. The open‐circuit voltage Voc is nearly proportional to the number of repetitions of the p‐i‐n unit cell. Almost‐constant energy‐conversion efficiencies of around 4% have been obtained with Voc ranging from 0.6 to 2.4 V by applying a simple optimum design rule to the cell‐construction parameters.

Sputtered hydrogenated amorphous silicon

Abstract: Hydrogenated a-Si, whose properties can be modified by impurity doping, can be produced either by decomposition of silane or by reactive sputtering of Si in an argon-hydrogen plasma. This article reviews advances made during the past few years in the preparation and characterization of films produced by the second method. The basic deposition conditions are summarized. The conclusions of analytical studies (photo-emission, infrared spectroscopy, and volumetric measurements of evolved gases), regarding the amount of hydrogen and its bonding configuration in the network, are outlined. The optical, carrier transport, photoconductivity and photoluminescence properties as a function of hydrogen content and doping are described. Electron drift mobilities, deduced from steady state and transient photoconductivity are presented. The transport and recombination properties are discussed with existing models of amorphous semiconductors, and are found to be consistent with atomic relaxations, i.e. polaronic effects.

Small-Angle-Scattering Evidence of Voids in Hydrogenated Amorphous Silicon

Abstract: The observation of extensive small-angle x-ray scattering from hydrogenated $a$-Si indicates that the void distribution in this material is very similar to that for evaporated $a$-Si. Thus the improved electrical properties of the hydrogenated material are not due to this material having a homogeneous structure.

Thin film solar cell

Abstract: PURPOSE: To obtain a highly efficient device with characteristics resisting against environmental conditions including moisture and contaminated matters by a method wherein an amorphous solar cell in which the division of elements is not difficult is used, increase in number of elements being not related to the increase in quantity of processes and costs. CONSTITUTION: An electrode in the shape of paste 2 of silver series is printed and calcined on the surface of a glass board 1 constituting the light receiving surface of a solar cell. This electrode 2 is composed of a bus bar portion for connecting the interior portions of light receiving surfaces together and a grid electrode to be connected to both sides. Next ITO transparent material for the electrode is evaporated covering the whole surface of the electrode 2 of the board 1, and the board is etched to produce a pattern desired and form an ITO transparent electrode. After this process, an amorphous silicon thin film 4 is formed, so that an element layer of the solar cell having the structure of n + -n - -P + can be obtained. Next an electrode 6 is formed, then the amorphous silicon elements are connected together in series. Thence an organic passivation film 7, lead wire 8, resin layer 9 for protection etc. are provided. COPYRIGHT: (C)1980,JPO&Japio

Importance of argon pressure in the preparation of rf‐sputtered amorphous silicon–hydrogen alloys

Abstract: We report the influence of argon partial pressure pAr on the photoconductivity, four‐probe conductivity and photoluminescence of rf‐sputtered a‐Si–H alloys. As pAr is increased from 5 to 30 mTorr, for fixed hydrogen partial pressure pH, photoconductivity increases by as much as three orders of magnitude and then saturates. Over this range the dark conductivity activation energy decreases, a plot of log conductivity versus inverse temperature becomes increasingly less linear and the photoluminescence intensity increases slightly and then drops back. We note that high pAr films become slowly contaminated upon exposure to air. These results are interpreted in terms of a reduction in energetic silicon atom bombardment of the growing film with increased pAr. For our sputtering arrangement, we show that silicon atoms ejected from the target become significantly more thermalized at pAr=10 mTorr than at 5 mTorr. Based primarily on the fact that the conductivity activation energy is more strongly dependent on pH f...

Graphoepitaxy of silicon on fused silica using surface micropatterns and laser crystallization

Abstract: Uniform crystallographic orientation of silicon films, 500 nm thick, has been achieved on amorphous fused silica substrates by laser crystallization of amorphous silicon deposited over surface‐relief gratings etched into the substrates by reactive ion etching. The gratings had a square‐wave cross section with a 3.8 μm spatial period, a 100–nm depth and corner radii of about 5 nm. The 〈100〉 directions in the silicon were parallel to the grating to within ±18°, and perpendicular to the substrate plane to within ±2.5°. A simple model for the graphoepitaxy process is presented. Sheet resistivity of phosphorous doped graphoepitaxial silicon was 2.5 times larger than that of bulk silicon of the same doping. Graphoepitaxy is a new application of microstructure fabrication that may lead to new combinations of substrates and overlayer films, and perhaps to three‐dimensionally integrated electronic devices and other novel configurations.

Photoconductive imaging using hydrogenated amorphous silicon film

Abstract: Highly resistive hydrogenated amorphous‐silicon film has been fabricated and examined as blocking‐type photoconductive target of a vidicon‐type image pickup tube. The results indicate that this novel silicon vidicon has many advantages over conventional ones.

Substrate and doping effects upon laser‐induced epitaxy of amorphous silicon

Abstract: UHV‐deposited amorphous silicon was recrystallized on (100) single‐crystal substrates using pulsed Nd : YAG laser irradiation Prior to deposition, substrates were prepared with either atomically clean surfaces, residual argon ion sputter damage, or from one to three monolayers of residual oxide Epitaxial regrowth of bulk crystalline quality occurred regardless of substrate preparation Annealing energy densities were significantly higher, however, for substrates retaining residual impurities Certain layers were doped with Ga At moderate doping levels recrystallization behavior was unaffected At a 2% doping level, the annealing energy threshold dropped by one‐half and Ga atoms were displaced toward the epitaxial surface It is shown that the decrease in energy threshold is due to an impurity‐induced increase in light absorption within the amorphous layer Layers were crystallized with substitutional Ga concentrations of up to 10 times the equilibrium solid solubility limit