Showing papers on "Amorphous silicon published in 1977"

Electrical and optical properties of amorphous silicon carbide, silicon nitride and germanium carbide prepared by the glow discharge technique

Abstract: Amorphous specimens of silicon carbide, silicon nitride and germanium carbide have been prepared by decomposition of suitable gaseous mixtures in a r.f. glow discharge. Substrates were held at a temperature T d between 400 and 800 K during deposition. In all three of the above materials the results of optical absorption and of d.c. conductivity measurements show a systematic variation with T d and with the volume ratio of the gases used. Electron microprobe results on silicon carbide specimens indicate that a wide range of film compositions can be prepared. The optical gap has a pronounced maximum at the composition Si00–32C0–68 where it is 2·8 eV for a sample deposited at T d = 500 K, but shifts to lower energies with increasing T d. The conductivity above about 400 K has a single activation energy approximately equal to half the optical gap and extended state conduction predominates if the silicon content exceeds 32%. If the latter is reduced, hopping transport takes over and it is suggested th...

Influence of 16O, 12C, 14N, and noble gases on the crystallization of amorphous Si layers

Abstract: Channeling effect measurements have been used to study the effect of impurities on the epitaxial regrowth of amorphous silicon layers on single‐crystal silicon. Implantation was used to form the amorphous layers and also to introduce the impurities 12C, 14N, 16O, 20Ne, 40A, and 84Kr. For 16O implants, the growth rate at 550 °C depended on the 16O concentration and at the level of 0.5 at.% the rate was reduced from about 90 to about 10 A/min. For similar atomic concentrations of 14N, the rate was comparable to the 16O case. For comparable concentrations of 12C, the regrowth rate was found to be three times higher than for that of the 16O case. Noble gas ions are also found to retard the growth rate of the amorphous layers. For 40Ar at about the 0.5‐at.% level, the regrowth rate is appreciably slower than even that for the 16O case.

Amorphous silicon solar cells

Abstract: The status of a-Si solar cell technology is reviewed. This review includes a discussion of the types of solar cell structure that are being used in commercial products. An overview of the development efforts under way involving new materials, such as alloys and microcrystalline films, and their impact on device performance is given. The status of stability in a-Si solar cells and projections for costs for large-scale manufacturing facilities are reviewed. The development of markets for a-Si photovoltaics is also discussed. >

Quantitative analysis of hydrogen in glow discharge amorphous silicon

Abstract: We report measurements of the hydrogen concentrations and densities of amorphous silicon films prepared from glow discharge plasmas of silane. Quantitative results are obtained from the resonant nuclear reaction 15N+1H→12C+4He+γ by counting the emitted γ rays. Mass spectrographic analysis of the gases evolved upon heating are also used to estimate the relative hydrogen concentrations for different preparation conditions. Comparisons are given to previously reported infrared absorption results and to electron microprobe estimates.

Optical and photoconductive properties of discharge‐produced amorphous silicon

Abstract: Optical and photoconductive properties of discharge‐produced amorphous silicon (a‐Si) of the type used in efficient thin‐film solar cells have been studied as a function of a wide range of deposition conditions The optical absorption, optical band gap, photoconductivity, hydrogen content, and the characteristics of the Si‐H vibrational mode in a‐Si were determined Both substrate temperature in the range ∼200–400 °C and the type of discharge used are found to be important factors in determining the measured optical and photoconductive properties of a‐Si For films produced at substrate temperatures near 200 °C, dihydride bonding occurs, and the optical band gap is about 17 eV As the substrate temerature increases, monohydride bonding is favored, the optical band gap decreases, the optical absorption increases, and the photoconductive properties improve These properties are, in part, associated with the presence of bonded hydrogen For substrate temperatures between 300 and 400 °C, the photoconductive

Photoconductivity and recombination in doped amorphous silicon

Abstract: The photoconductivity αph and its dependence on incident light intensity and temperature have been investigated in a series of doped amorphous silicon specimens at a photon energy of 2 eV. Specimens were prepared by the glow discharge decomposition of silane at a substrate temperature between 500 and 550 K. Doping was achieved by the addition of controlled amounts of phosphine or diborane during deposition. The primary aim of the work has been to explore the recombination process and its dependence on the known density of state distribution using substitutional doping to control the dark Fermi levels position over a range of 0·8 eV. It is shown that [sgrave]ph attains its optimum level when at a given temperature and intensity the steady-state electron Fermi level has been moved to an energy between 0·35 and 0·30 eV below the mobility edge, ∊ c . At this stage there also occurs a transition from predominantly monomolecular to bimolecular recombination. Both effects appear to be associated with th...

Electron and hole drift mobility in amorphous silicon

Abstract: Electron and hole drift mobility have been measured in n‐ and p‐type amorphous Si Schottky‐barrier solar cells. At room temperature μdn= (2–5) ×10−2 cm2/V sec and μdp= (5–6) ×10−4 cm2/V sec. Both mobilities are trap controlled with ΔE=0.19 eV for electrons and ΔE=0.35 eV for holes above 250 °K and ΔE=0.16 and 0.26 eV, respectively, below 250 °K. Majority‐carrier lifetimes are estimated to be 1 μsec for electrons and 25 μsec for holes.

Thermoelectric power in phosphorous doped amorphous silicon

Abstract: Thermoelectric power and conductivity measurements have been made as a function of temperature on a series of a-Si specimens doped substitutionally with phosphorous. The samples were prepared by the glow discharge decomposition of silane containing predetermined concentrations of phosphine. The thermoelectric power of all the samples investigated was negative as expected. For the lightly doped specimens the thermoelectric and conductivity results support the model developed from previous work. Electron transport is in the extended states, but below room temperature there is an increasing contribution from tail state hopping. At higher doping concentrations the data can be interpreted in terms of transport through the extended states and the localized donor states, as suggested by the analysis of recent Hall effect results. The value of the intercept S 0 on the S axis at 1/T = 0 depends strongly on the position of the Fermi energy ∊F with respect to the mobility edge at ∊c. The movement of ∊F with...

Electronic properties of amorphous silicon in solar cell operation

Abstract: Amorphous silicon (a-Si) solar cells, which have efficiencies up to 5.5 percent, are unique in several ways, and their cell characteristics no longer depend on the same parameters generally considered in single crystal cells. This paper discusses the operation of such cells, and relates the major new parameters to the electronic properties of a-Si which are highly dependent on the densities of gap centers in this disordered material. The effect of the photoconductivity in intrinsic a-Si on the series resistance of the cell, the quality of a-Si junctions and their ability to transport current densities generated under AM1 illumination are presented. Space-charge densities as low as 5 × 1015cm-3are found in a-Si junctions, which are orders of magnitude lower than previous estimates for glow discharge produced a-Si. The effects of electric field distributions and diffusion lengths of holes on collection efficiencies and cell characteristics are discussed and illustrated. Although significant trapping of photogenerated holes is found in many of the a-Si films, diffusion lengths of few tenths of a micron are also indicated by the results presented.

Photoluminescence of hydrogenated amorphous silicon

Abstract: Amorphous silicon obtained by the glow‐discharge decomposition of silane can contain on the order of 18–50 at.% of hydrogen. Heating this material above 350 °C causes the evolution of H2. The photoluminescence efficiency decreases with increasing hydrogen depletion.

Coordination of Arsenic Impurities in Amorphous Silicon-Hydrogen Alloys

Abstract: We have determined the coordination of arsenic impurities in amorphous silicon-hydrogen alloys prepared by plasma decomposition of silane-arsine mixtures. From analysis of the extended x-ray absorption fine structure (EXAFS) on the arsenic $K$-shell absorption, we find at low arsenic concentrations that an average of two arsenic atoms in ten are fourfold coordinated with silicon. This is the first direct evidence for the occurrence of substitutional doping in an amorphous semiconductor.

Image forming method

Abstract: PURPOSE:To obtain good images by performing electrolytic reaction by using the hydrogenated amorphous silicon of controlled electrical characteristics as a photosensitive layer CONSTITUTION:A photosensitive layer substrate 21 made by depositing a hydrogenated amorphous silicon layer 12 on a conductive substrate 11 is put into electrolyte 23 For example, an aqueous soln of zinc acetate of 001mol/l is used as the electrolyte Next, a subject 26 is imaged on the photosensitive layer substrate 21 through a transparent wall 28 by a lamp 25 and a lens system 27 In this state, a constant voltage DC power source 29 is connected in a manner that a counter electrode 24 acts as anode and the conductive substrate 11 as cathode, and a voltage of about 5V is applied Thence, according to the exposure, zinc will deposit on the surface of the layer 12

Solar cells using discharge-produced amorphous silicon

Abstract: Thin film solar cells, ≲ 1 μm thick, have been fabricated in p-i-n and Schottky barrier structures using d.c. and r.f. glow discharges in silane. Conversion efficiencies in the range of 2.5 to 4.0% have been obtained with both structures. The p-i-n cells exhibit built-in potentials of ∼ 1.1 V while the Pt Schottky barrier cells have barrier heights of ∼ 1.1 eV. The dark currents in the p-i-n cells appear to be recombination-limited while the Schottky barrier cells exhibit near-ideal diode characteristics with diode quality factors near unity.

Amorphous silicon-amorphous silicon carbide photovoltaic device

Abstract: A layer of amorphous silicon-carbide prepared by a glow discharge in a mixture of silane, hydrocarbon and doping gases is at the solar radiation incident surface of a photovoltaic device. The photovoltaic device includes first and second contiguous layers of amorphous silicon fabricated by a glow discharge in silane. The amorphous silicon carbide layer is contiguous to the second layer and opposite the first layer. The amorphous silicon carbide layer is substantially transparent to solar radiation and highly conductive, providing increased solar radiation collection efficiency and reduced internal resistance.

Interstitial doping of amorphous silicon

Abstract: Interstitial doping of glow‐discharge a‐Si has been achieved by in‐diffusion and implantation of lithium. After doping with about 1% Li, we observe an increase of room‐temperature conductivity by a factor of 106 and a decrease in the activation energy of conductivity down to 0.17 eV. Corresponding changes are observed for the thermoelectric power which, as expected for n‐type material, has a negative sign.

The use of nuclear reactions and SIMS for quantitative depth profiling of hydrogen in amorphous silicon

Abstract: Depth profiles for hydrogen in amorphous silicon have been determined by the use of resonant nuclear reactions [1H(15N,αγ)12C and 1H(19F,αγ)16O] and by secondary ion mass spectroscopy (SIMS). Independent calibration procedures were used for the two techniques. Measurements were made on the same amorphous silicon film to provide a direct comparison of the two hydrogen analysis techniques. The hydrogen concentration in the bulk of the film was determined to be about 9 at.% H. The SIMS results agree with the resonant nuclear reaction results to within 10%, which demonstrates that quantitative hydrogen depth profiles can be obtained by SIMS analysis for materials such as amorphous silicon.

Photoluminescence in pure and doped amorphous silicon

Abstract: Luminescence and excitation spectra are reported for undoped glow discharge a-Si, and a range of n and p-type samples produced by substitutional doping. At low temperatures the doped samples show evidence of a strong, non-activated quenching process, probably due to charged defects.

Photogeneration of charge carriers and recombination in amorphous semiconductors

Abstract: A discussion is given of the recombination, both radiative and non-radiative, of electron-hole pairs in amorphous silicon and chalcogenides.

Amorphous silicon photovoltaic device having an insulating layer

Abstract: In a photovoltaic semiconductor device, an electrically insulating layer is between and in contact with a body of amorphous silicon fabricated by a glow discharge in silane and a metallic film of a metal capable of forming a surface barrier junction with the amorphous silicon body. The insulating layer is of such a relatively thin thickness that charge carriers are capable of tunneling through the insulating layer. The insulating layer has been found to increase the open circuit voltage of the photovoltaic device without adversely affecting the short circuit current density of the device.

Passivation of metallized semiconductor substrates

Abstract: Disclosed is a method and structure for protecting circuit components from the ambient and in particular for protecting the contact metal from the adverse effects of moisture. A first layer of amorphous silicon is deposited over the circuit including the metal contacts. A second layer which may be silicon nitride or silicon dioxide is then deposited over the amorphous silicon. The amorphous silicon layer reduces cracking in the second layer and prevents cracks in the second layer from propagating to the circuit components.

Silicon films as selective absorbers for solar energy conversion

Abstract: The optical constants below the fundamental absorption edge (up to 5 μm) of silicon single crystals and sputtered amorphous silicon films at high temperatures (up to 800°C) have been determined and the photothermal efficiencies of silicon–metal selective absorbers for thermal solar energy conversion calculated.

Method of forming diodes by amorphous implantations and concurrent annealing, monocrystalline reconversion and oxide passivation in N-type silicon

Abstract: Boron implantation regions in N-type silicon are subjected to a severe damage implant before anneal in a strongly oxidizing atmosphere that provides a passivating silicon dioxide surface layer. Diodes are formed having leakages as low as when such regions are annealed in other atmospheres or are formed in silicon. In a preferred example, BF 2 + is used to simultaneously implant boron into a region and convert it to amorphous silicon.