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7 June 2013

RPI’s Smart Lighting ERC demos first monolithic integration of LED and HEMT on GaN chip

The Smart Lighting Engineering Research Center at Rensselaer Polytechnic Institute (RPI) in Troy, NY, USA has demonstrated what is reckoned to be the first monolithically integrated light-emitting diode (LED) and high-electron-mobility transistor (HEMT) on the same gallium nitride (GaN) chip. It is reckoned that the development could open the door to a new generation of LED technology which is less expensive to manufacture, much more efficient, and which enables new functionalities and applications beyond illumination.

In existing LED lighting systems, for the LED to function, external components — such as inductors, capacitors, silicon interconnects, and wires — must be installed on or integrated into the chip. Due to these essential components, the large size of the chip complicates the design and performance of LED lighting products. Additionally, the process of assembling the complex LED lighting systems can be slow, manually intensive, and expensive.

In a study ‘Monolithic integration of light-emitting diodes and power metal-oxide semiconductor channel high-electron-mobility transistors for light-emitting power integrated circuits in GaN on sapphire substrate’ (Appl. Phys. Lett. 102, 192107 (2013)) led by T. Paul Chow, professor in the Department of Electrical, Computer, and Systems Engineering (ECSE) at RPI, the researchers hence sought to develop a chip with components all made from GaN. The monolithically integration simplifies LED device manufacturing, requiring fewer assembly steps and less automation. Also, LED devices made with monolithically integrated chips will have fewer parts to malfunction, higher energy efficiency and cost effectiveness, and greater lighting design flexibility, it is reckoned.

Picture: Cross-section of RPI’s monolithically integrated GaN LED and HEMT.

The research team grew a GaN LED structure directly on top of a GaN HEMT structure. Using basic techniques to interconnect the two regions, they created what is reckoned to be the first monolithic integration of a HEMT and an LED on the same GaN-based chip. The device, grown on a sapphire substrate, demonstrated light output and light density comparable to standard GaN LED devices. Chow reckons that the study is a key step toward creating a new class of optoelectronic device: the light-emitting integrated circuit (LEIC).

“Just as the integration of many silicon devices in a single chip — integrated circuits — has enabled powerful compact computers and a wide range of smart device technology, the LEIC will play a pivotal role in cost-effective monolithic integration of electronics and LED technology for new smart lighting applications and more efficient LED lighting systems,” Chow says.

Picture: Monolithically integrated LED and HEMT, with the LED off (left) and on (right).

“LEICs will result in even higher energy efficiency of LED lighting systems,” comments Smart Lighting ERC director Robert Karlicek, a co-author of the study and ECSE professor at RPI. “But what will be even more exciting are the new devices, new applications, and new breakthroughs enabled by LEICs — they will truly usher in the era of smart lighting.”

Along with Chow and Karlicek, co-authors of the paper are: Christian Wetzel, the Wellfleet Constellation Professor of Future Chips at Rensselaer and a faculty member in the Department of Physics, Applied Physics, and Astronomy; Rensselaer graduate students Zhongda Li and John Waldron; and former Rensselaer research associate professor Theeradetch Detchprohm.

The research was funded by the US National Science Foundation (NSF) through the Smart Lighting ERC, with additional support from New York state though Empire State Development’s Division of Science, Technology and Innovation (NYSTAR).




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