There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

This short communication reports on achieving 18·8% total-area conversion efficiency for a ZnO/CdS/Cu(In,Ga)Se2/Mo polycrystalline thin-film solar cell. We also report a 15%-efficient, Cd-free device fabricated via physical vapor deposition methods. The Cd-free cell includes no buffer layer, and it is fabricated by direct deposition of ZnO on the Cu(In,Ga)Se2 thin-film absorber. Both results have been measured at the National Renewable Energy Laboratory under standard reporting conditions (1000 W/m2, 25°C, ASTM E 892 Global). The 18·8% conversion efficiency represents a new record for such devices (Notable Exceptions) and makes the 20% performance level by thin-film polycrystalline materials much closer to reality. We allude to the enhancement in performance of such cells as compared to previous record cells, and we discuss possible and realistic routes to enhance the performance toward the 20% efficiency level. Published in 1999 by John Wiley & Sons, Ltd. This article is a US government work and is in the public domain in the United States.

Progress toward 20% efficiency in Cu(In,Ga)Se2 polycrystalline thin‐film solar cells

Chalcopyrite copper indium sulfide (CuInS2) and copper indium gallium selenide (Cu(InxGa1-x)Se2; CIGS) nanocrystals ranging from ∼5 to ∼25 nm in diameter were synthesized by arrested precipitation in solution. The In/Ga ratio in the CIGS nanocrystals could be controlled by varying the In/Ga reactant ratio in the reaction, and the optical properties of the CuInS2 and CIGS nanocrystals correspond to those of the respective bulk materials. Using methods developed to produce uniform, crack-free micrometer-thick films, CuInSe2 nanocrystals were tested in prototype photovoltaic devices. As a proof-of-concept, the nanocrystal-based devices exhibited a reproducible photovoltaic response.

Synthesis of CuInS2, CuInSe2, and Cu(InxGa1-x)Se2 (CIGS) Nanocrystal “Inks” for Printable Photovoltaics

Optical Waveguide Theory

An important milestone in the development of photovoltaic thin‐film solar cells is the achievement of 15% conversion efficiency. This letter describes the highest efficiency single junction thin‐film cell reported to date. An active area efficiency of 14.8% is obtained with the cell structure n‐ZnO/n‐CdS/p‐CuInSe2 deposited on a soda‐lime glass substrate. The current achievements are due to improved properties of the CuInSe2 layer and the heterojunctions compared to previously reported results. The rate and substrate temperature profiles used during the coevaporation process yield a relatively large‐grained material with very strong 〈112〉 orientation and low porosity. This results in reduced recombination rates, hence higher open circuit voltage and fill factor.

ZnO/CdS/CuInSe2 thin‐film solar cells with improved performance

SrS:Ce is an intensively investigated phosphor due to its blue‐green electroluminescence, which shows efficient blue emission after filtering. Recently reported devices based on this material have demonstrated a luminous efficiency of 1.6 lm/W. The luminescence properties of SrS:Ce,X (X=Na or Cl) have been studied on powders and thin films. It is shown that a high density of traps in SrS:Ce,X occurs. The interaction of Ce3+ with traps gives rise to a phosphorescence. An energy transfer from Ce3+ to traps is responsible for an observed luminescence quenching in the presence of high electric fields. Moreover, the traps are electrically active and are involved in the electroluminescence process. The observed energy transfer is proposed to be the dominant excitation mechanism of Ce3+ in electroluminescence. It is demonstrated for thin films that the defect density increases with doping; therefore, the luminescence yield is already limited at doping concentrations below the onset of the concentration quenching. Thus, the prepared SrS:Ce,Cl thin films show a lower photoluminescence yield than powders. It is concluded that an undisturbed Ce incorporation into SrS thin films has not been achieved so far, although high electroluminescence efficiencies (1.6 lm/W) have been obtained.

Luminescence properties of SrS:Ce3+

A multi-source reactive deposition process for preparing a phosphor layer for an AC TFEL device having the chemical formula MII MIII 2 X4 :RE, where MII is a group II metal taken from the group magnesium, calcium, strontium and barium, MIII is a group III metal taken from the group aluminum, gallium and indium, X is taken from the group sulfur and selenium, and RE comprises a rare earth activator dopant taken from the group cerium and europium is disclosed. The phosphor film is formed in crystalline form on a substrate heated to a temperature between 400° and 800° C. by depositing more than one deposition source chemical where at least one of the deposition source chemicals of the group II metal or the group III metal is a compound.

Multi-source reactive deposition process for the preparation of blue light emitting phosphor layers for AC TFEL devices

Solar cells based on CuIn(Se, S)2

We demonstrate excellent 40 Gbit/s operation of a packaged InP Mach-Zehnder-Modulator with a low rms jitter of 730 fs. A modulator with 63 GHz on-chip bandwidth is shown as a step towards 80 Gbit/s transmission.

Karl-Otto Velthaus

Papers

ZnO/CdS/CuInSe2 thin‐film solar cells with improved performance

Luminescence properties of SrS:Ce3+

Multi-source reactive deposition process for the preparation of blue light emitting phosphor layers for AC TFEL devices

Solar cells based on CuIn(Se, S)2

1.55μm Mach-Zehnder Modulators on InP for Optical 40/80 Gbit/s Transmission Networks