Zinc oxide nanoparticles significantly improve LED performance

Researchers at the Georgia Institute of Technology have used zinc oxide nanowires to significantly improve the efficiency of gallium nitride LEDs in converting electrical current into ultraviolet light.

By applying mechanical strain to the nanowires, the researchers created a piezoelectric potential in them. This potential was used to adjust the transport of charges and enhance carrier injection in LEDs. This control of optoelectronic devices by piezoelectric potential is called the piezo-photoelectric effect. This effect increases the rate at which electrons and holes recombine to produce photons and enhances the external performance of the device by up to 4 times by increasing the luminous intensity and increasing the injected current.

A professor at the school's Department of Materials Science and Engineering said that in practical terms, this new effect can have many effects on photoelectric processes, including improving the energy efficiency of lighting devices. Traditional LEDs generally use structures such as quantum wells to trap electrons and holes, which requires the two to stay close enough for a long time to recombine. The longer the electrons and holes are close, the higher the efficiency of the LED device. Although the internal quantum efficiency of a general LED can reach 80%, the external efficiency of a traditional single pn junction thin-film LED is only 3%.

The zinc oxide nanowires in the new device form the n of the pn junction, and the gallium nitride film can serve as the p. Free carriers will be trapped in this interface region. The piezoelectric-photoelectric effect can increase the luminous intensity by 17 times and the node current by 4 times when 0.093% compressive stress is applied to the device, thereby increasing the photoelectric conversion rate by about 4.25 times. Under the action of appropriate external stress, the external efficiency of the new device can reach 7.82%, which greatly exceeds the external quantum efficiency of traditional LEDs.

The LEDs made by the research team can emit ultraviolet light with a wavelength of about 390 nanometers, but the professor believes that it can be extended to the visible light range in the future and be suitable for various optoelectronic devices. At present, efficient ultraviolet emitters are needed in the fields of chemistry, biology, aerospace, military and medical technology.

The professor also said that this research has opened up a new field of using the piezoelectric-photoelectric effect to adjust optoelectronic devices. Significantly improving the efficiency of LED lighting equipment is expected to bring considerable energy savings, which is very important for applications in the field of green and renewable energy technology. In addition, this discovery can also be applied to other optical devices controlled by electric fields.