For the reactors used in the manufacture of LED’s there are more promising materials than the ones currently in use, the researchers point out.
There are many new possibilities for the development of gallium nitride (GaN) used in the production LEDs. One of the most promising production methods of gallium nitride is the ammonothermal method which uses a reactor filled up with liquid ammonia. The method is identical with the hydrothermal method utilised in the production of quartz, in which water is used instead of ammonia.
However, the high temperature inside the ammonothermal reactor combined with a pressure 2,500 times the atmospheric pressure and the corrosive effects of the so-called supercritical fluid pose a challenge to the reactor chamber and thus to the manufacture of LED materials. To find a solution to the problem, Aalto University Post-Doctoral Researcher Sami Suihkonen and a research group from the University of California, Santa Barbara led by Nobelist in Physics Shuji Nakamura and Post-Doctoral Researcher Siddha Pimputkarsystematically analysed the behaviours of 35 metals, 2 metalloids and 17 different ceramic materials with 3 different supercritical fluid chemistries heated to a temperature of 572 degrees Celsius.
In the ammonothermal method, the energy contained in the reactor corresponds roughly to a stick of dynamite.
– In the ammonothermal method, the energy contained in the reactor corresponds roughly to a stick of dynamite, making the conditions fairly hostile, Sami Suihkonen sums up.
Princeton University researchers have developed a new method to increase the brightness, efficiency and clarity of LEDs, which are widely used on smartphones and portable electronics as well as becoming increasingly common in lighting.
Using a new nanoscale structure, the researchers, led by electrical engineering professor Stephen Chou, increased the brightness and efficiency of LEDs made of organic materials (flexible carbon-based sheets) by 57 percent. The researchers also report their method should yield similar improvements in LEDs made in inorganic (silicon-based) materials used most commonly today.
The method also improves the picture clarity of LED displays by 400 percent, compared with conventional approaches. In an article published online August 19 in the journal Advanced Functional Materials, the researchers describe how they accomplished this by inventing a technique that manipulates light on a scale smaller than a single wavelength.
“New nanotechnology can change the rules of the ways we manipulate light,” said Chou, who has been working in the field for 30 years. “We can use this to make devices with unprecedented performance.”
A LED, or light emitting diode, is an electronic device that emits light when electrical current moves through two terminals. LEDs offer several advantages over incandescent or fluorescent lights: they are far more efficient, compact and have a longer lifetime, all of which are important in portable displays.
Current LEDs have design challenges; foremost among them is to reduce the amount of light that gets trapped inside the LED’s structure. Although they are known for their efficiency, only a very small amount of light generated inside an LED actually escapes.
“It is exactly the same reason that lighting installed inside a swimming pool seems dim from outside – because the water traps the light,” said Chou, the Joseph C. Elgin Professor of Engineering. “The solid structure of a LED traps far more light than the pool’s water.”