Organic Laser Diode Suppresses Losses, Lowers Electricity Requirements

Lasing by direct electrical stimulation of an organic film is possible, according to researchers at Kyushu University, who have demonstrated a laser diode based on organic semiconductors.

Organic laser diodes produce a pure light, but they require currents that are magnitudes higher than those used in OLEDs to achieve the lasing process, said the researchers. The high resistance to electricity of many organic materials makes it difficult to get enough electrical charges in the materials before they heat up and burn out. Additionally, a variety of loss processes inherent to most organic materials and devices operating under high currents lowers efficiency, pushing the necessary current up even higher.

An organic laser diode emitting blue laser light, as reported by researchers at Kyushu University’s Center for Organic Photonics and Electronics Research. Courtesy of Atula S.D. Sandanayaka.

To overcome these challenges and successfully demonstrate an organic laser diode, a research group led by professor Chihaya Adachi used a highly efficient organic light-emitting material, called BSBCz, which has a relatively low resistance to electricity and a low amount of losses, even when injected with large amounts of electricity.

The researchers designed a device structure with a grid of insulating material on top of one of the electrodes used to inject electricity into the organic thin films. Such grids, called distributed feedback structures, are known to produce the optical effects required for lasing. “By optimizing these grids, we could not only obtain the desired optical properties but also control the flow of electricity in the devices and minimize the amount of electricity required to observe lasing from the organic thin film,” Adachi said.

Schematic representation of an organic semiconductor laser diode producing blue laser emission under electrical excitation. Courtesy of the Center for Organic Photonics and Electronics Research, Kyushu University.

The researchers observed laser emission under current injection. They attributed successful emission to the clear separation of the lasing wavelength from significant absorption, due to charge carriers and triplet excitons, to the reduction of optical losses due to electrical contacts, because of the distributed feedback architecture, to the low lasing threshold of the BSBCz films, which allowed the researchers to observe current-injection lasing before device degradation took place.

The researchers have founded the startup company KOALA Tech Inc. — short for Kyushu Organic Laser Technology Inc. — to accelerate their research and overcome the final obstacles that they believe remain before organic laser diodes can be used in commercial applications. The founding members of KOALA Tech Inc. are now at work improving the performance of their organic laser diodes for use in applications such as biosensing, displays, health care, and optical communications.

Authors of the paper by professor A.S.D. Sandanayaka et al., entitled “Indication of current-injection lasing from an organic semiconductor.” Courtesy of the Center for Organic Photonics and Electronics Research, Kyushu University.

“I think that many people in the community were doubting whether we would actually one day see the realization of an organic laser diode, but by slowing chipping away at the various performance limitations with improved materials and new device structures, we finally did it,” said professor Atula S.D. Sandanayaka.

Organic laser diodes use carbon-based organic materials to emit light instead of inorganic semiconductors, such as gallium arsenide and gallium nitride.

The research was published in Applied Physics Express (http://dx.doi.org/10.7567/1882-0786/ab1b90).