Self-Assembled DNA Basis Serves as Semiconductor in MSM Photodetector
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RESEARCH/RESEARCHERS Bromine-Doped Pentacene Acts as a Phototransistor with Gain over a Large Spectral Range Recent interest in the development of organic compounds for application as electronic devices has been stimulated in part by the capability of depositing the compounds over large areas on flexible substrates and at a low manufacturing cost. Doped-pentacene thin films have the potential to work as field-effect transistors (FETs) or photovoltaic diodes due to their high charge carrier mobility. Doping of pentacene enhances the benefits obtained from its electronic properties, and this represented an advantage for Jan Hendrik Schön and Christian Kloc from Bell Laboratories/Lucent Technologies when they fabricated an optically activated FET, as they reported in the May 28 issue of Applied Physics Letters. The researchers obtained such a device by using bromine-doped pentacene, which becomes a p-type semiconductor. Single crystals of pentacene, 1-µm thick, were grown from vapor in a flow of hydrogen. The source and drain contacts were 300-nm-thick gold strips deposited by shadow masking, and the Schottky gate electrode was a 30-nm-thick aluminum strip. A Xe lamp and a monochromator or a He-Ne laser was used to illuminate the device. As the device is normally off, it develops a potential barrier at the AlSchottky contact. In this case, the drain current increases with increasing gate bias and saturates with increasing drain voltage. The operative conditions of this device can be manipulated by changing the dopant amount, film thickness, or Schottky barrier height. Illumination changes the behavior of the drain current and causes the device response to increase abruptly when the energy of the light quanta are equivalent
MgB22 Superconductors Superconductors MgB Update Available Update Available
The surprising discovery discovery of 39 K superconThe of 39 K ductivity in crystallographically simsuperconductivity in crystallographiple MgB launched 2 in January cally simple MgB2 inhas January hasa flurry ofa flurry intense international launched of intense internaresearch and development activities, tional research and development as scientists search for higher activities, as scientists search fortransihightion temperatures (Tc ) as well er transition temperatures (Tc )as asbetter well understanding and improvement of as better understanding and improveMgB2of ’s MgB materials characteristics. See ment ’s materials characteris2 the See Materials Research Society Web tics. the Materials Research Society site for on recent findings Web sitean forupdate an update on recent findpresented at at the ings presented the2001 2001MRS MRS Spring Spring Meeting: www.mrs.org/meetings/ www.mrs.org/meetings/ Meeting: spring2001/news/mgb2.html. spring2001/news/ mgb2.html.
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to that of the absorption edge of the semiconductor. This device seems to act in a similar manner to a photodiode which, however, incorporates the amplification of a FET. Changes in the illumination intensity affect the voltage at the gate and therefore affec
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