Crystal promises more light

Chip-based devices that emit or absorb light, like light-emitting diodes, are relatively inexpensive and increasingly efficient, but they are limited by spontaneous emission -- the tendency to uncontrollably fire off photons in all directions.

Spontaneous emission lowers the efficiency of devices designed to control light and also produces noise that can interfere with signals to make the devices less precise.

Researchers from Kyoto University have demonstrated a device that inhibits spontaneous emission by redirecting the energy to a useful purpose. The method could lead to more efficient light-emitting diodes, lasers, displays, solar cells, and quantum-information systems.

The researchers' device is a 5-nanometer-wide light-emitting bit of semiconductor material embedded in a two-dimensional photonic crystal. Photonic crystal is a material that contains regularly-spaced holes that block light. The size of the holes controls the range of wavelengths that can travel through the crystal.

Most photonic crystal devices contain areas without holes that channel light. The researchers' crystal has holes throughout. The researchers made different crystals with holes ranging from 174 to 290 nanometers and spaced 300 to 500 nanometers center-to-center. A nanometer is one millionth of a millimeter.

The material blocked five times as much spontaneously-emitted light in the plane of the crystal and emitted five times as much light from the surface of the device as non-photonic-crystal chips, according to the researchers.

The method has the potential to dramatically increase the efficiency of increasingly popular light-emitting diode lights, according to the researchers. The work could be used practically in three to five years, according to the researchers.

The work appeared in the May 27, 2005 issue of Science (Simultaneous Inhibition and Redistribution of Spontaneous Light Emission in Photonic Crystals). -TECHNOLOGY RESEARCH NEWS