Showing papers on "Amorphous silicon published in 1986"

Infrared spectroscopic study of SiOx films produced by plasma enhanced chemical vapor deposition

Abstract: We have studied the local atomic structure of silicon suboxide (SiOx, x<2) thin films using infrared (IR) spectroscopy. The films were prepared by plasma enhanced chemical vapor deposition (PECVD) of silane (SiH4) and nitrous oxide (N2O) mixtures, which were then diluted with He. The IR spectra were found to vary significantly with the degree of He dilution. Films grown with no He showed SiN, NH, and SiH bonding groups in addition to the three characteristic vibrations of the Si–O–Si linkage. The addition of He reduced the strength of the SiN, NH, and SiH absorption bands, and resulted in systematic increases in the frequency of the Si–O–Si asymmetric stretching vibration. The frequency of this Si–O–Si stretching vibration scales linearly with the oxygen concentration from approximately 940 cm−1 in oxygen doped amorphous silicon to 1075 cm−1 in stoichiometric noncrystalline SiO2. A deposition temperature of 350 °C and a He dilution of 50% gave a film composition close to SiO1.9. We propose a model for the...

Plasma deposited thin films

Abstract: This book presents a discussion of the mechanisms and practice of plasma deposition with particular emphasis on significant materials produced by this technique, and their applications Materials discussed include hydrogenated amorphous silicon and its alloys, amorphous carbon, and the critically important insulators such as silicon nitride, carbide, and oxide In addition, a review is given, with extensive references, of many other potentially useful materials A major theme of this book is the interrelationship between the process, the authors' understanding of the properties of materials, together with device fabrication and ultimate performance Over 150 figures complement the text

Film formation mechanisms in the plasma deposition of hydrogenated amorphous silicon

Abstract: By studying the step coverage of plasma‐deposited amorphous silicon and germanium on patterned substrates, we find that the film formation process under device‐quality deposition conditions has a substantial component that behaves like a surface rate‐limited chemical vapor deposition process, while conditions producing defective material are associated with a much more physical‐vapor‐deposition‐like process. An explanation involving surface reactions of SiHx radicals is proposed.

Enhancement of open circuit voltage in high efficiency amorphous silicon alloy solar cells

Abstract: We have developed a microcrystalline fluorinated p+ silicon alloy which has high dark conductivity and low optical loss. Incorporation of this material in single and tandem amorphous silicon alloy based solar cells has resulted in increased open circuit voltage and conversion efficiency.

Multiple-quantum NMR study of clustering in hydrogenated amorphous silicon.

Abstract: Multiple-quantum nuclear-magnetic-resonance techniques are used to study the distribution of hydrogen in hydrogenated amorphous silicon. Using the fact that multiple-quantum excitation is limited by the size of the dipolar-coupled spin system, we show that the predominant bonding environment for hydrogen is a cluster of four to seven atoms. For device quality films, the concentration of these cluster defects increases with increasing hydrogen content. At very high hydrogen content, the clusters are replaced with a continuous network of silicon-hydrogen bonds.

Catalytic Chemical Vapor Deposition (CTC–CVD) Method Producing High Quality Hydrogenated Amorphous Silicon

Abstract: A new method of producing high quality hydrogenated amorphous silicon (a-Si:H) films is presented. An SiH4. and H2 gas mixture is decomposed without using any plasmas or photochemical excitation, but using only thermal and catalytic reactions between deposition-gas and a heated tungsten catalyzer. Photoconductivity of films produced by this methodreaches 10-3 (Ωcm)-1 and photosensitivity exceeds 105 for illumination of AM-1 light of 100 mW/cm2.

Transport phenomena in amorphous silicon doped by ion implantation of 3d metals

Abstract: Charge transport in amorphous silicon (aSi) doped with ion implantation of Mn+, Ni+, Fe+, and Cu+ ions is studied using ESR technique, temperature dependence of conductivity σ(T), and thermopower α(T) measurements With increasing of impurity (Mn, Ni, Fe) concentration (from 1018to 1019 cm−3) the localized state density and σ decrease owing to the passivation of silicon dangling bonds with impurity atoms An analysis of conductivity and thermopower data allows to reveal three temperature regions 1) At 250 500 K electron transport dominates 3) At T < 250 K hopping conductivity with variable range hopping near Fermi level prevails For a-Si:Mn in the region of 4 < T < 80 K Coulomb correlations are detected in the behaviour of σ(T) The Coulomb gap is foundto reach a maximum value 25 meV which appears to be one order of value larger than the known (one) in semiconductors doped with shallow impurity levels [Russian Text Ignored]

Metastable defects in amorphous-silicon thin-film transistors.

Abstract: When a positive gate voltage is applied to an amorphous-silicon thin-film transistor, electrons become trapped in states close to the silicon-dielectric interface. This is studied by a new technique involving the transient discharge current produced under illumination. It is suggested that the behavior may involve metastable dangling bonds generated within the amorphous silicon as a consequence of the field-effect-induced increase in electron concentration. This constitutes an important new instability mechanism for amorphous-silicon thin-film transistors.

Investigation of the growth kinetics of glow-discharge hydrogenated amorphous silicon using a radical separation technique

Abstract: The deposition kinetics of hydrogenated amorphous silicon (a‐Si:H) from a SiH4 glow‐discharge plasma have been investigated by examining the diffusion of SiH3 monoradicals in the discharge‐free space within a triode reactor. This experiment suggests that the SiH3 radicals are responsible for about 37% of the total deposition rate of a‐Si:H in a conventional SiH4 glow‐discharge process. The contribution of other radicals and atoms to the deposition rate is also discussed through the analysis of reaction‐rate constants.

Thermal equilibration in doped amorphous silicon.

Abstract: The structure of doped amorphous silicon is shown to be in metastable thermal equilibrium above 130\ifmmode^\circ\else\textdegree\fi{}C, having temperature-dependent densities of dangling bonds and donors. The time to reach equilibrium is thermally activated, so that cooling establishes a slowly relaxing nonequilibrium state resembling a glass. The results are interpreted in terms of the recent defect-compensation model of doping.

Hydrogenated microvoids and light-induced degradation of amorphous-silicon solar cells

Abstract: Amorphous-silicon solar cells generally exhibit a degradation of conversion efficiency in the first few weeks of exposure to sun light. This degradation is associated with metastable defect centers that influence many of the properties of hydrogenated amorphous-silicon. This paper discusses a model for these metastable centers that is based on the assumption that holes can be trapped near microvoids and can induce the motion of hydrogen on the internal surfaces of the microvoids.

Amorphous silicon p-i-n solar cells with graded interface

Abstract: The influence of inserting a thin graded interface layer at the p/i interface on the short‐wavelength response and on the overall performance of amorphous silicon p‐i‐n solar cells is discussed. This device structure has resulted in fill factor values as high as 0.771.

In situ spectroscopic ellipsometry study of the growth of microcrystalline silicon

Abstract: High sensitivity, high‐energy resolution, and the capability to obtain data in situ make ellipsometry a useful tool for addressing a number of problems in thin‐film deposition processes. Dielectric functions e=e1−i e2 of glow‐discharge‐produced microcrystalline silicon films (μc‐Si) are determined by using spectroscopic ellipsometry (SE). e2 spectra present a shoulder near 4.2 eV which corresponds to the E2 optical transition observed in crystalline silicon. This peak is not observed in amorphous silicon spectra. c‐Si is described as a mixture of amorphous phase, microcrystallites, and voids. The choice of the microcrystalline reference phase is discussed in particular by comparing the microcrystallite volume fraction determined from SE and x‐ray measurements. Strong variations in the nature of the material are observed during growth: the density deficiency and the surface roughness both increase as functions of film thickness up to 0.4–0.5 μm.

Magnetic recording medium

Abstract: PURPOSE:To obtain a thin metallic film type flexible magnetic recording medium having excellent mechanical durability by having a thin ferromagnetic metallic film and amorphous silicon layer formed on a flexible substrate and further a lubricating layer formed on the amorphous silicon layer. CONSTITUTION:The thickness of the flexible substrate 1 is preferably about 4-100mum and the thickness of the thin ferromagnetic metallic film 2 is preferably 0.01-2mum. The amorphous silicon layer 3 is formed on the thin ferromagnetic metallic film by a method such as sputtering using Si as a target. The amorphous silicon layer has the wear resistance specific to an amorphous material and since the layer is in an amorphous state, many unpaired electrons exist therein. The lubricating layer 5 which is chemically active and is hardly strippable by binding securely with a lubricating agent is formed. The medium having high durability even if the lubricating agent is directly coated on the layer is obtd. The much higher durability is obtd. if a surface treatment layer 4 consisting of fluorinated silane is provided therebetween.

Explosive crystallization in silicon

Abstract: A survey of the possible autocatalytic crystallization processes called explosive crystallization in liquid and solid states is given. The explosive liquid‐phase epitaxy with laterally moving coupled interfaces of melting and crystallization in amorphous silicon layers on insulators is investigated by the use of an experimental equipment consisting of three synchronized lasers supplying the temperature pulses for ignition, spreading, and stopping of the explosive front. The velocity of this explosive crystallization front measured by use of time‐resolved reflectivity of a test beam is compared with the results of model calculations. The results are in good agreement. The crystal structure was investigated by optical and transmission electron micrography and represents crystalline laminae grown preferentially in the 〈110〉 direction over a distance of about 100 μm. Areas of some millimeters in diameter can be crystallized by this method.

Electronic transport in doped amorphous silicon.

Abstract: The temperature dependence of the dc dark conductivity of doped hydrogenated amorphous silicon is explained by the defect-compensation model of doping with the proposal that the structure is in metastable thermal equilibrium. Observed conductivity activation energies and preexponential factors can be accounted for quantitatively. When the localized state distribution is in thermal equilibrium, the conductivity preexponential factor is the Mott minimum metallic conductivity.

Laser Patterning Method for Integrated Type a-Si Solar Cell Submodules

Abstract: A laser patterning method was investigated as a fabrication method for integrated-type amorphous-silicon (a-Si) solar cell submodules. A three-dimensional thermal analysis of a multilayer structure was performed to determine the selective scribing conditions for each layer of an a-Si solar cell. The optimum laser power densities calculated from a three-dimensional thermal analysis were confirmed by the experiments. It was found that not only transparent conductive oxide and a-Si films, but also the metal electrodes of the integrated-type a-Si solar cell submodule were selectively scribed. The total output power of an a-Si solar cell submodule patterned by optimum laser-power densities was 9% higher than that achieved by a conventional patterning method.

Multilayer semi-insulating film for hermetic wafer passivation and method for making same

Abstract: A film for hermetically passivating monocrystalline silicon includes sequential layers of undoped amorphous silicon, oxygen doped polycrystalline silicon, silicon rich oxynitride, and silicon nitride, and may be overlaid with an organic bulk dielectric such as polyimide The inorganic film accurately sets the monocrystalline surface Fermi potential, independent of ambient electrical, mechanical, thermal, ionic, and moisture conditions A method for depositing the amorphous silicon and the oxygen doped polycrystalline silicon layers of the film includes sequentially reacting monosilane in an inert carrier gas, such as helium or argon, and nitrous oxide The layers are blended by varying the deposition temperature, the nitrous oxide flow rate, the monosilane flow rate, the monosilane dilution, and the inert carrier gas species The layers are annealed to locally segregate the oxygen, to grow the grains to the proper size, and to set the final recombination velocity of the monocrystalline region

A chemical-bond approach to doping, compensation and photo-induced degradation in amorphous silicon

Abstract: We propose that during deposition of a-Si:H films a chemical equilibrium is established that relates the density of dangling-bond defects near mid-gap to the densities of electrons and holes in the conduction and valence band states. We develop the appropriate chemical reaction formalism and show that our model allows doping, compensation and photo-induced degradation to be treated within a single and unifying approach.

Reaction mechanism and kinetics of silane pyrolysis on a hydrogenated amorphous silicon surface

Abstract: Three regimes of pressure and temperature are identified in which silane pyrolysis has distinctly different initial kinetics: in two regimes the initial reactions are heterogeneous and in the third regime it is homogeneous. We report here a preliminary model for the heterogeneous reaction regime where the decomposition rate is nearly independent of pressure. In the model the silicon surface is saturated with hydrogen and hence is nonreactive. The rate limiting step for silane decomposition is the creation of reactive surface sites by release of hydrogen. These reactive sites are refilled by decomposition of SiH4 or reincorporation of H2. A new adsorbed state of SiH4 is proposed which is bound to the surface by a three‐center bond. After making some simplifications to the full model the kinetics are solved for static‐ and flowing‐gas hot wall reactor experiments. The implications of the proposed reactions for the other two pyrolysis regimes and for silane discharges are briefly discussed.

Electrophotographic sensitive body

Abstract: PURPOSE:To obtain the titled body having an improved adhesion between a substrate and an photoconductive layer and an improved photoconductive property by constituting the titled body of a pure aluminum which forms an alumite layer not contg. a crystal water on a substrate and an photoconductive layer composed of a hydrogenated amorphous silicon layer. CONSTITUTION:The substrate is worked to an appropriate cylindrical shape and is composed of aluminum 1 which has >=99.5% a purity, and forms the alumite layer 2 not contg. the crystal water thereon. The photoconductive layer composed of the hydrogenated amorphous silicon layers 3 is laminated on the surface of the alumite layer 2, and the surface layer 4 made of a hydrogen contg. amorphous boron nitride is laminated on the photoconductive layer in order. The alumite layer 2 has a double structure composed of a barrier layer 2a and a porous layer 2b. The hydrogen content contd. in the hydrogenated amorphous silicon layer 3 is <=20atom%, preferably 5-13atom%.

Direct measurements of the velocity and thickness of ‘‘explosively’’ propagating buried molten layers in amorphous silicon

Abstract: Simultaneous infrared (1152 nm) and visible (633 nm) reflectivity measurements with nanosecond resolution were used to study the initial formation and subsequent motion of pulsed KrF laser‐induced ‘‘explosively’’ propagating buried molten layers in ion implantation‐amorphized silicon. The buried layer velocity decreases with depth below the surface, but increases with KrF laser energy density; a maximum velocity of about 14 m/s was observed, implying an undercooling‐velocity relationship of ∼14 K/(m/s). Z‐contrast scanning transmission electron microscopy was used to form a direct chemical image of implanted Cu ions transported by the buried layer and showed that the final buried layer thickness was <15 nm.

Annealing of metastable defects in hydrogenated amorphous silicon.

Abstract: The annealing process of light-induced metastable dangling-bond states in hydrogenated amorphous silicon is studied using the analysis presented in the preceding paper for electron-spin-resonance transients. The annealing kinetics are monomolecular, with a thermally activated decay rate R=${\ensuremath{ u}}_{0}$exp(-${E}_{a}$/${\mathrm{kT}}_{A}$). The decay curves of the metastable defects in pure, UHV-deposited a-Si:H and in a-Si:N,H a-Si:C,H and a-Si:O,H with impurity contents between 1 and 20 at.?are analyzed in terms of a well-defined prefactor, ${\ensuremath{ u}}_{0}$, and a broad distribution of thermal activation energies, N(${E}_{a}$). Both ${\ensuremath{ u}}_{0}$ and N(${E}_{a}$), depend in a characteristic way on the density and the chemical nature of the impurities present in a sample. Moreover, a strong correlation between ${\ensuremath{ u}}_{0}$ and N(${E}_{a}$) similar to the Meyer-Neldel rule for the conductivity in a-Si:H is observed. Implications of the experimental results for the intrinsic or extrinsic nature of the metastable defects and possible annealing mechanisms are discussed.

Assessment of lattice relaxation effects in transitions from mobility gap states in hydrogenated amorphous silicon using transient photocapacitance techniques

Abstract: We have employed junction photocapacitance and thermal transient capacitance measurements in n‐type doped hydrogenated amorphous silicon and have identified, within each of a series of samples, the optical transitions: D−→D0+e and D0→D++e, and the thermal transitions: D−→D0+e and D+→D0+h, where D−, D0, and D+ denote the three charge states of Si dangling bond defect. We have also correlated the optical and thermal transitions associated with the valence bandtail states. Lattice relaxation energies are found to be less than 0.1 eV for the dangling bond transitions, but as large as 0.5–0.6 eV for the valence bandtail states. We also determined a value of Ueff for the D−/D0 splitting of 0.24±0.07 eV.

Amorphous silicon ionizing particle detectors

Abstract: Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation

Manufacture of semiconductor device

Abstract: PURPOSE:To coat the roughened surface of the semiconductor substrate with an insulating film at a comparatively low temperature and to make gentle the surface by a method wherein an amorphous silicon film with a good covering property is deposited on the insulating film in an atmosphere of plasma CONSTITUTION:Impurity diffusion layers 2 are formed in a single crystal silicon substrate 1 and a silicon oxide film 3 is formed on the single crystal silicon substrate 1 Moreover, after that, polycrystalline silicon wiring layers 4, which act as the gate of a transistor and a wiring, are formed The state of the surface of the semiconductor substrate in this stage is in a state that a comparatively steep roughness of a thickness of 2-3,000Angstrom to 7-8,000Angstrom is formed on the surface An amorphous silicon film 5 of a thickness of about 4,000Angstrom is deposited by decomposing silane gas in an atmosphere of plasma in such a way that this roughness is sufficiently coated with the amorphous silicon film 5 After this, the amorphous silicon film 5 is made to completely oxidize by performing a wet oxidation at about 600 degC to form a silicon oxide film 6

Method of manufacturing a semiconductor device using amorphous silicon as a mask

Abstract: A method of manufacturing a semiconductor device has the steps of forming an insulating film on a semiconductor substrate, forming a polycrystalline silicon layer on the insulating film, converting either all of the polycrystalline silicon layer or a portion of predetermined thickness of the polycrystalline silicon layer into an amorphous silicon layer, patterning the polycrystalline silicon layer, either all of which or a portion of predetermined thickness of which has been converted into an amorphous silicon layer, and ion-implanting an impurity in the semiconductor substrate using the patterned layer as a mask.

New high field‐effect mobility regimes of amorphous silicon alloy thin‐film transistor operation

Abstract: A new theory of a‐Si thin‐film transistor (TFT) operation is presented. In addition to the below‐ and above‐threshold regimes described previously, it predicts two new regimes of operation which occur at very high densities of the induced charge in the a‐Si TFT channel. In a crystallinelike regime the free‐electron concentration exceeds the localized charge concentration at the a‐Si‐insulator interface. In a transitional regime (at lower densities of the induced charge) almost all localized states in the energy gap of amorphous silicon near the interface are filled. In the crystallinelike regime, the field‐effect mobility is close to the band mobility and the operation of an a‐Si TFT is truly similar to the operation of a crystalline field‐effect transistor. Our estimates show that the gate voltage necessary to achieve the crystallinelike regime is about 50 V for an a‐Si TFT with an insulator 1000 A thick and a relative permittivity of approximately 3.9.

Fast and slow states at the interface of amorphous silicon and silicon nitride

Abstract: The effects of a graded composition layer at the amorphous silicon/nitride interface are studied using transient photoconductivity. The graded layer causes a large increase in the density of slow states (electrons trapped within the nitride), but does not influence the fast interface states. The kinetics of trapping and release are measured and a model of field assisted hopping and thermal excitation is proposed. The different origins of slow and fast states are also discussed.