A novel organic semiconductor device from Cornell University researchers uses ionic junctions that electroluminesce and act as a photovoltaic cell. The idea could lead to displays on cloth or paper, and cheap solar cells. Organic semiconductors can be made in thin, flexible sheets. And, "Flexible means low-cost fabrication,"says George Malliaras, Cornell-associate professor of materials-science and engineering. "Large quantities could be made cheaply by feeding films from rolls." Semiconductors organic or otherwise are materials that contain either an excess of free electrons (N-type) or "holes" ( Ptype). Holes are spaces where an atom ought to have an electron but doesn't, representing a positive charge. N and P-type materials can be joined to form diodes and transistors. The Cornell group went a step further by making a diode out of organic semiconductors that also contain free ions, molecules with an electrical charge. They laminated two organic layers, one containing free positive ions, and the other, negative ions. They then added thin conducting films on top and bottom; the top conductor is transparent to let light in and out. Where the two films meet, negative ions migrate across the junction to the positive side and vice versa, until reaching equilibrium. This is analogous to what takes place in a silicon diode, where electrons and holes migrate across the junction, say researchers. A voltage applied across the top and bottom electrodes makes current flow through the junction. The migration of ionic charge across the junction causes a higher voltage potential than normal and affects the way electrons combine with holes. This raises the energy of the molecules, which quickly releases as intense light. Conversely, bright light shone on the device is absorbed by the molecules, causing them to kick out electrons. The ionic charges create a preferential direction for the electrons to move,
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General Purpose Diodes
General-purpose diodes are electric components that conduct electric current in only one direction, functioning similarly to a one-way valve.
Rectifier diodes are designed for use in rectification circuits. Rectifiers are used to convert AC to DC.
Radiation detectors are used for medical diagnoses, radioactive dating measurements, and measurements of background radiation, activity levels and radiation doses.
Electrolytes are electrically-conductive materials that are used in batteries, fuel cells, capacitors, and biochemical systems. They typically exist as ionic solutions, or as molten salts or solids.
Varactor diodes are p-n junction diodes that are designed to act as a voltage controlled capacitance when operated under reverse bias.
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9.2.3 Diodes, Junctions, and Recombination
The simplest semiconductor device is called a diode, a name meaning that it has two electrical terminals. The first electronic diodes were vacuum tubes that...
Most semiconductors are made by doping silicon with a material that creates free negative charge (N-type), or free positive charge (P-type). The fixed atoms have positive and negative charge,...
Some of the most important applications of quantum mechanics are in semiconductor physics and technology based on the properties of electrons in a periodic lattice of ions. This problem is discussed...
9.2.2 Electrons, Holes, and Doping
Electronic devices require higher conductivity. All it takes is a few impurities. To understand how that works, we will start by looking at silicon, the...
WHAT THEY ARE
As mentioned on page 141, a diode is an electronic device having two terminals. There are many types, but the most common one is the PN diode. This can "rectify" ac, by only allowing...