Absorption edge and internal electric fields in amorphous semiconductors
TL;DR: In this paper, a simple model based on the existence of internal electric fields is suggested to explain the exponential part of the absorption edge observed in many amorphous semiconductors.
About: This article is published in Materials Research Bulletin.The article was published on 1970-08-01. It has received 1150 citations till now. The article focuses on the topics: Absorption edge & Electric field.
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TL;DR: In this paper, the fabrication, properties, and solar energy applications of highly ordered TiO 2 nanotube arrays made by anodic oxidation of titanium in fluoride-based electrolytes are reviewed.
1,905 citations
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TL;DR: In this paper, experimental evidence about the states in the gap of chalcogenide glasses is discussed and the total concentration of states is estimated from the measurements of the magnetic susceptibility and their density distribution from the optical and photo-emission measurements.
Abstract: Experimental evidence about the states in the gap of chalcogenide glasses is discussed. The total concentration of states is estimated from the measurements of the magnetic susceptibility and their density distribution from the optical and photo-emission measurements. Possible models for the interpretation of the experimental facts are considered.
1,685 citations
TL;DR: In this paper, a chemical bonding model is developed which describes the arrangement of these sites and which accounts for many of the electronic and mechanical properties of amorphous carbon, including elastic modulus, hardness, wear rate, friction and film adhesion.
683 citations
TL;DR: It is indicated that the heterostructured combination of g-C3N4, Ag and TiO2 microspheres provides synergistic photocatalytic activity through an efficient electron transfer process.
Abstract: The visible-light photocatalytic performance of the heterostructured g-C3N4/Ag/TiO2 microspheres was investigated. As an electron-conduction bridge, Ag nanoparticles were photodeposited as the interlayer between g-C3N4 and the surface of TiO2 microspheres to increase visible-light absorption via the surface plasmon resonance. The interface between Ag/TiO2 and g-C3N4 facilitates the direct migration of photoinduced electrons from g-C3N4 to Ag/TiO2, which is conductive to retarding the recombination of electron–holes. The g-C3N4 (4%)/Ag/TiO2 microsphere sample shows significant photocatalytic activity, higher than the sum of g-C3N4 (1.2 mg) and Ag/TiO2 samples, or the sum of TiO2 and Ag/g-C3N4 (1.8 mg) samples. It indicates that the heterostructured combination of g-C3N4, Ag and TiO2 microspheres provides synergistic photocatalytic activity through an efficient electron transfer process.
572 citations
TL;DR: In this article, a real-time monitoring of the anodization current, at a fixed potential, is used to controllably eliminate the Ti layer underneath the titanium oxide nanotubes without disturbing the architecture.
Abstract: Titanium thin films, 400 nm to 1000 nm thick, fabricated by radio frequency (rf) sputter deposition are anodized in an electrolyte containing acetic acid and hydrofluoric acid to form optically transparent films of highly ordered titania nanotube arrays Real-time monitoring of the anodization current, at a fixed potential, is used to controllably eliminate the Ti layer underneath the titanium oxide nanotube array without disturbing the architecture Fabrication variables critical to achieving the transparent nanotube-array film include annealing temperature of the anodized, initially amorphous nanotube array and Ti-film sputter deposition variables, including rate, film thickness, and substrate temperature Structural investigations on the transparent nanotube arrays reveal only the presence of the anatase phase even after annealing at 500 °C In contrast, both rutile and anatase phases were observed in films with a metal layer underneath the nanotubes and annealed in an oxygen ambient above 430 °C Rutile growth occurs at the nanotube–metal interface as metal oxidation takes place during annealing The average refractive index of the transparent nanotube-array film is found to be 166 in the UV-vis range, with a calculated porosity of 67 %; the bandgap is determined as 334 eV, with a bandgap tail extending to 24 eV
472 citations
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4,546 citations
TL;DR: Amorphous covalent alloys particularly of group-IV, -V, and -VI elements are readily formed over broad ranges of composition and have been described as low-mobility electronic intrinsic semiconductors with a temperature-activated electrical conductivity σ = σ 0×exp(-ΔE/kT) which sometimes extends well into the molten state as discussed by the authors.
Abstract: Amorphous covalent alloys particularly of group-IV, -V, and -VI elements are readily formed over broad ranges of composition.1–6 They have been described as low-mobility electronic intrinsic semiconductors with a temperature-activated electrical conductivity σ = σ 0×exp(-ΔE/kT) which sometimes extends well into the molten state.2,3,7 They remain intrinsic with changed ΔE when their composition is changed.1,5,7 These alloys transmit infrared light up to an exponential absorption edge from which an energy gap E g is estimated.1,2 The value of E g usually is smaller than 2ΔE, often by as much as 10–20%.7,8 Photoconductivity9 and recombination-radiation10 measurements have been interpreted as giving evidence for the presence of localized states in the gap.
828 citations
TL;DR: In this article, a general theory of line-shapes of the exciton absorption bands is developed with the help of generating function, and the half-value width H is given by the level broadening of the optically produced K=O ex· citon due to lattice scattering, so that it is proportional to T except at low.temperatures.
Abstract: A general theory of line-shapes of the exciton absorption bands is developed with the help of generating function. method. When the exciton-lattice coupling is weak, and the exciton effective mass .. is ~all, the absorption band is of a Lorentzian shape, provided that the temperature T is not too high. The half-value width H is given by the level broadening of the optically produced K=O ex· citon due to lattice scattering, so that it is proportional to T except at low .temperatures. If the coupling is strong, or the exciton efFective mass is large, or the temperature is very high, the absorp tion band is expected to be of a Gaussian shape, and H is proportional to VT. The mutual influence of adjacent absorption bands is also discussed ; it causes the asymmetry and repulsion of the compo nents as temperature rises. If we replace T by the density of lattice imperfections, the ·above statements are valid, without substantial modifications, as regards the dependence on the degree of imperfections. These conclusions are in qualitative agreement with experimental data. The comparison further provides us with information on the strength of the exciton-lattice coupling and the energy band structure of the exciton.
523 citations
TL;DR: In this article, a semiquantitative calculation is made of such broadening due to impurities in semiconductors having direct absorption edges, and reasonable agreement is found with published absorption tails of InAs, for both the magnitude of the effect and its dependence on impurity concentration.
Abstract: The electric fields of charged defects in a solid broaden its fundamental optical absorption edge by a mechanism which is an internal analog of the Franz-Keldysh effect. Using this analogy, a semiquantitative calculation is made of such broadening due to impurities in semiconductors having direct absorption edges. Without the use of any adjustable parameters, reasonable agreement is found with published absorption tails of InAs, for both the magnitude of the effect and its dependence on impurity concentration. It is proposed that such effects account for the common Urbach's rule observations, and a qualitative discussion is given for the corresponding effects in insulators.
214 citations
204 citations