[High-tech LED News] Recently, researchers at the Georgia Institute of Technology in the United States have used zinc oxide nanowires to significantly improve the efficiency of GaN LEDs to convert current into ultraviolet light.
By applying mechanical strain on the nanowires, the researchers created piezoelectric potentials in them. This potential is used to adjust the charge transfer and enhance the carrier injection of the LED. This piezoelectric potential control of the optoelectronic device is referred to as the piezoelectric-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 four times by increasing the intensity of the illumination and increasing the injection current.
According to the professor of materials science and engineering at the school, from the actual situation, this new effect can have many effects on the photoelectric process, including improving the energy efficiency of the lighting device. Conventional LEDs typically use structures such as quantum wells to trap electrons and holes, which requires the two to remain close enough for recombination for a long time. The longer the electrons and holes are close, the higher the efficiency of the LED device. Although the internal quantum efficiency of a typical LED can reach 80%, the external efficiency of a conventional single pn junction thin film LED is only 3%.
The zinc oxide nanowires in the new device constitute n of the pn junction, and the gallium nitride film can be used as p therein. Free carriers will be imprisoned in this interface area. Piezoelectric-photoelectric effect can increase the luminous intensity by 17 times and the junction current by 4 times when the device is subjected to 0.093% compressive stress, thereby increasing the photoelectric conversion rate by about 4.25 times. Under the action of suitable external stress, the external efficiency of the new device can reach 7.82%, which greatly exceeds the external quantum efficiency of the traditional LED.
The LEDs produced by the research team can emit ultraviolet light with a wavelength of about 390 nm, but the professor believes that the future can be extended to the visible range, suitable for all types of optoelectronic devices. Currently, efficient UV emitters are needed in the chemical, biological, aerospace, military, and medical technologies.
The professor also said that the study opened up a new field of optoelectronic equipment using piezoelectric-photoelectric effects. Significantly increasing the efficiency of LED lighting equipment is expected to bring considerable energy savings, which is important for applications in green and renewable energy technologies. In addition, this discovery can be applied to other optical devices controlled by electric fields.
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