Optoelectronic devices that emit warm and cool white light

December 21, 2020

The advantages of light-emitting diodes (LEDs), such as their tiny size, low cost and excellent power efficiency, mean they are found everywhere in modern life. A KAUST team has recently developed a way of producing a white-light LED that overcomes some critical challenges.

Blinking away on almost every modern electronic device, LEDs transmit messages in their own distinct shade of red, green or blue. The coloration of an LED comes from a semiconductor inside that emits over a narrow spectrum of optical wavelengths. The inability of LEDs to emit across a wider spectrum restricts their use in lighting applications -- emitting a wider spectrum is necessary to generate white light -- or for displays that require a wide palette of different colors.

One approach to fabricate white-light LEDs is to combine devices of different materials, where each material emits a different color. The emission of red, blue and green from the different materials can be combined to create white light, but this increases the complexity and cost of manufacture of LEDs. Alternatively, a single semiconductor can be used by mixing in a phosphor that absorbs some of the light emitted by the semiconductor and then re-emits it as a different color. However, phosphor degrades over time, limiting the useful lifetime of these devices.

Daisuke Iida and Kazuhiro Ohkawa's team have devised a way to build phosphor-free monolithic white-light LEDs using the semiconductor indium gallium nitride.

The emission color of indium gallium nitride depends on the relative content of the indium and gallium atoms. For example, gallium nitride emits ultraviolet light, but adding indium shifts the emission across the visible spectrum and into the infrared. The emission can be controlled further by sandwiching very thin layers of indium gallium nitride with one composition between two layers of different composition, creating so-called quantum wells.

"What is unique about our devices is that we use material defects, or V-pit structures, to enhance the injection of a current into the semiconductor," says Iida. The LEDs designed by the KAUST team included both blue-light emitting quantum wells with a 20 percent indium content and 34 percent indium red quantum wells. Combined, this monolithic LED emits light across the entire visible spectrum. By controlling the current passing through the device, the team could change the emission from a warm white to a natural white and through to a cool white.

"The next step is to improve the emission efficacy of the red emission component," says Iida. "The red emission is a key factor of the high color-rendering LEDs with the natural white emission."

King Abdullah University of Science & Technology (KAUST)

Related Semiconductor Articles from Brightsurf:

Blue phosphorus: How a semiconductor becomes a metal
Blue phosphorus, an atomically thin synthetic semiconductor, becomes metallic as soon as it is converted into a double layer.

A new method to measure optical absorption in semiconductor crystals
Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

Medical robotic hand? Rubbery semiconductor makes it possible
A medical robotic hand could allow doctors to more accurately diagnose and treat people from halfway around the world, but currently available technologies aren't good enough to match the in-person experience.

Laser allows solid-state refrigeration of a semiconductor material
A team from the University of Washington used an infrared laser to cool a solid semiconductor by at least 20 degrees C, or 36 F, below room temperature, as they report in a paper published June 23 in Nature Communications.

Scientists create smallest semiconductor laser
An international team of researchers announced the development of the world's most compact semiconductor laser that works in the visible range at room temperature.

Clemson researcher's novel MOF is potential next-gen semiconductor
Clemson professor Sourav Saha demonstrated a novel double-helical metal organic framework architecture in a partially oxidized form that conducts electricity, potentially making it a next-generation semiconductor.

A gold butterfly can make its own semiconductor skin
A nanoscale gold butterfly provides a more precise route for growing/synthesizing nanosized semiconductors that can be used in nano-lasers and other applications.

Scientists pioneer new generation of semiconductor neutron detector
In a new study, scientists have developed a new type of semiconductor neutron detector that boosts detection rates by reducing the number of steps involved in neutron capture and transduction.

Scientists see defects in potential new semiconductor
A research team has reported seeing, for the first time, atomic scale defects that dictate the properties of a new and powerful semiconductor.

Bending an organic semiconductor can boost electrical flow
Slightly bending semiconductors made of organic materials can roughly double the speed of electricity flowing through them and could benefit next-generation electronics such as sensors and solar cells, according to Rutgers-led research.

Read More: Semiconductor News and Semiconductor Current Events
Brightsurf.com 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 Amazon.com.