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  • Diode Breaks Electronics Speed Record
Jan 2004
WASHINGTON, Jan. 30 -- Engineers have fused a 1950s concept with modern semiconductor processing and design to create a diode that can move electrical current at record-breaking rates.

At room temperature, the diode (a device that behaves like a valve for electricity traveling within a circuit) can transmit current equivalent to 151,000 amps per square centimeter, three times the rate of its closest competitors. (Standard home wiring carries a maximum current density of only 700 amps per square centimeter.)

Known in the research community as a "resonant interband tunneling diode," the silicon-based semiconductor has applications in computers and other electronic devices nd may eventually boost cellular phone signals to reach communications towers now beyond their range.

Niu Jin and Paul Berger next to the rapid thermal annealing system used in their research. (Photo: Paul Berger, Ohio State University, NSF)

Paul Berger, Niu Jin (lead author) and their colleagues at Ohio State University in Columbus, Phillip Thompson at the Naval Research Laboratory in Washington, D.C., and Roger Lake at the University of California at Riverside, announced their world current record in the journal Applied Physics Letters. They developed the diode with the support of the National Science Foundation (NSF).

Tunneling diodes have been around since the late 1950s, when Leo Esaki, then at Sony Corp. in Japan, discovered that a property called tunneling can increase a diode’s output current. Esaki later won the Nobel Prize, in part for this work.

Tunneling is a process that takes place at the level of the atom, in the realm of quantum physics. At that scale, the familiar rules of classical physics that guide rocket design, snowfall and baseball give way to less intuitive rules based on probability, waves and energy packets.

Under the rules of quantum physics, an electron on one side of a barrier can travel through to the other side, "which would be like a tennis ball coming out the other side of a brick wall," says Berger. Although the property, called tunneling, is somewhat mysterious, researchers have been taking advantage of the phenomenon for years, although only in niche applications.

Phillip E. Thompson of the Naval Research Laboratory next to his molecular beam epitaxy system. (Photo: Phillip E. Thompson, Naval Research Laboratory)

By tweaking the properties of semiconductors, researchers can create materials that increase the chances that tunneling will occur. Berger and his team have optimized the diode design and the process for creating the device with few imperfections. The researchers also developed a manufacturing process to create tunneling diodes that, in addition to being incredibly fast, are silicon-based and easy to mass produce.

The original tunnel diodes were difficult to mass produce and were not compatible with the silicon-based microchips that run modern electronics devices.

By infusing silicon with large amounts of dopants (atoms in semiconductors that change the silicon crystal structure and allow electrons to flow) and controlling the temperatures at which the crystals grow, the team created a diode that was ideal for high-tunneling currents.

The researchers are negotiating with a major electronics manufacturer to develop the device for uses in wireless and mixed-signal applications and have already integrated the diode with devices that are used in cell phones and standard computer chips in another NSF-supported project completed in conjunction with Rochester Institute of Technology.

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A two-electrode device with an anode and a cathode that passes current in only one direction. It may be designed as an electron tube or as a semiconductor device.
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