Red-light LEDs for next-generation displays

July 05, 2020

In efforts to optimize the performance of light-emitting diodes (LEDs), KAUST researchers are looking at every aspect of the design, fabrication and operation of these devices. Now, they have succeeded in fabricating red LEDs, based on the naturally blue-emitting semiconductor indium gallium nitride, that are as stable as those based on indium gallium phosphide.

LEDs are optical sources made from semiconductors that offer improvements on conventional visible-light sources in terms of energy saving, smaller size and longer lifetimes. LEDs can emit across the spectrum, from the ultraviolet to blue (B), green (G), red (R) and into the infrared. And arrays of tiny RGB devices, so-called micro-LEDs, can be used to make vivid-color displays, which could underpin the next generation of monitors and televisions.

A major challenge facing the development of microLEDs is to integrate red, green and blue light into a single LED chip. Current RGB LEDs are made by combining two kinds of materials: red-light LEDs are made of indium gallium phosphide (InGaP), while blue and green LEDs comprise indium gallium nitride (InGaN) semiconductors. Integrating two material systems is difficult. "Creating RGB displays requires the mass transfer of the separate blue, green and red LEDs together," says KAUST researcher Zhe Zhuang. An easier solution would be to create different-colored LEDs all on a single semiconductor chip.

Since InGaP semiconductors are unable to emit blue or green light, the only solution to making monolithic RGB micro-LEDs is to use InGaN. This material has the potential to shift its emission from blue to green, yellow and red by introducing more indium into the mix. And InGaN red LEDs have been predicted to have better performance than the current InGaP ones.

Zhuang, Daisuke Iida, Kazuhiro Ohkawa and their colleagues have succeeded in growing high-quality indium-rich InGaN to fabricate red LEDs using the nanofabrication facilities at the KAUST Core Labs.

The team also developed excellent transparent electrical contacts using a thin film of indium-tin-oxide (ITO)1, which allows for a current to pass through their InGaN-based amber and red LEDs. "We have optimized the fabrication of the ITO film to realize low electrical resistance and high transmittance". The team demonstrated that these characteristics significantly improved the performance of InGaN red LEDs. They also carefully studied InGaN red LEDs of different sizes and at various temperatures. Changes in temperature affect the output light power and cause different color impressions, making them crucial for practical device performance.

"A critical disadvantage of InGaP red LEDs is that they are not stable when operated at high temperatures," explains Zhuang. "Therefore, we created InGaN red LEDs of different designs to realize very stable red-light InGaN sources at high temperatures." They have developed an InGaN red LED structure where the output power is more stable than that of InGaP red LEDs2. Also, its emission color shift at high temperatures was less than half of that of those made with InGaP.
This paper was selected as the Editor's Pick in the journal of Applied Physics Letters, highlighting the value of this research.

King Abdullah University of Science & Technology (KAUST)

Related Semiconductors Articles from Brightsurf:

Scientists develop method to detect charge traps in organic semiconductors
Scientists at Swansea University have developed a very sensitive method to detect the tiny signatures of so called 'charge traps' in organic semiconductors.

Liquid metals come to the rescue of semiconductors
Two-dimensional semiconductors offer a possible solution to the limited potential for further shrinking of traditional silicon-based electronics: the long-predicted end of 'Moore's Law'.

Shedding light on the development of efficient blue-emitting semiconductors
Scientists at Tokyo Institute of Technology (Tokyo Tech) have discovered a new alkali copper halide, Cs5Cu3Cl6I2, that emits pure blue light.

Theoretical prediction of reverse intersystem crossing for organic semiconductors
A team of Japanese researchers developed a method to predict rate constants of reverse intersystem crossing (RISC) associated with light emission efficiency of organic semiconductors used for OLED through quantum chemical calculations with computers.

2D semiconductors found to be close-to-ideal fractional quantum hall platform
Columbia University researchers report that they have observed a quantum fluid known as the fractional quantum Hall states (FQHS), one of the most delicate phases of matter, for the first time in a monolayer 2D semiconductor.

Extensive review of spin-gapless semiconductors: Next-generation spintronics candidates
An Australian has published an extensive review of spin-gapless semiconductors (SGSs), a new class of 'zero bandgap' materials which have fully spin polarised electrons and holes, and first proposed in 2008 by the review team's lead, Professor Xiaolin Wang (University of Wollongong).

2D molecular crystals modulating electronic properties of organic semiconductors
Recently, researchers report a controllable surface doping strategy utilizing 2D molecular crystals (2DMCs) as dopants to boost the mobility and to modulate the threshold voltage of OFETs.

Shedding new light on nanolasers using 2D semiconductors
Cun-Zheng Ning, a professor of electrical engineering in the Ira A.

The future of semiconductors is clear
Mobility is a key parameter for semiconductor performance and relates to how quickly and easily electrons can move inside a substance.

Semiconductors can behave like metals and even like superconductors
The crystal structure at the surface of semiconductor materials can make them behave like metals and even like superconductors, a joint Swansea/Rostock research team has shown.

Read More: Semiconductors News and Semiconductors Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to