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Cornell achieves a new record in deep ultraviolet photonics

Thursday, October 5, 2017

Figure: a) Transmission electron microscope image showing atomically thin gallium nitride (GaN in aluminum nitride (AIN) layers to produce 219 nm deep ultraviolet light; b) the molecular beam epitaxy machine to perform crystal growth of ultra-thin crystals; c) enhancement of internal quantum efficiency achieved by new GaN/AIN design compared to conventional AlGaN/AlGaN designs; d) vertical alignment of electron-hole wavefunction is believed to cause the IQE enhancement for the new design.

Deep-ultraviolet (DUV) light emitting diodes (LEDs), with a wavelength of less than 280 nanometers convert electrical power to photon power. DUV LEDs are useful for germicidal applications like purification and disinfecting water, air, food and beverages. However, the efficiency of current state-of-the-art DUV LEDs is still low compared to LEDs used for ambient lighting. In fact, only as much as two percent of the consumed electrical power is converted to DUV light, which is comparable to the performance of incandescent light bulbs.

A research group led by Cornell Engineering Professors Debdeep Jena and Grace Xing recently achieved 40% internal quantum efficiency (IQE) for DUV emission at 219 nanometer-wavelength from gallium nitride/alumnimum nitride (GaN/AIN) heterostructures.[1]

Internal quantum efficiency (IQE) is one of the three components of the overall electrical efficiency of an LED. The researchers say that the 40% IQE is more than twice the highest-reported value for the conventional AlGaN QW-based heterostructures at comparable short DUV wavelengths. As such, it is considered the new record.

While increasing the electrical current can increase the power emitted by a DUV LED, this also increases the amount of heat the LED produces. In addition, the lifespan of a DUV LED decreases as the level of electrical current is increased.

By improving the efficiency of DUV LEDs, they can be used for more applications and with longer lifespans. More efficient and powerful DUV LEDs also reduce treatment time and the need for cooling and consequently, create a more attractive and cost effective alternative to existing solutions for disinfection purposes, including mercury-based Ultraviolet C (UVC), a subtype of ultraviolet light also used as a germicide.

 “We hope our work will lead to rugged, portable, high-efficiency semiconductor light sources for DUV applications such as water/air purification, bio-photonic diagnostics, sterilization, food preservation, security and environment monitoring, and industrial curing,” said SM Moududul Islam, Ph.D., a Postdoctoral Associate in electrical and computer engineering with the Jena/Xing group and the lead author of the study.

Jena and Xing both have joint appointments with the School of Electrical and Computer Engineering and the Department of Materials Science at Cornell University.

 



[1] SM (Moudud) Islam et al, Appl. Phys. Lett., vol111, p091104, 2017

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