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LEDs and power transistors share a GaN-on-sapphire chip

Scientists have demonstrated what they claim is the first monolithic integration of an LED and High-Electron-Mobility Transistor (HEMT) on a single gallium nitride chip
Researchers from the Smart Lighting Engineering Research Centre at Rensselaer Polytechnic Institute (RPI) have successfully integrated an LED and a power transistor on the same GaN chip.

This innovation could open the door to a new generation of LED technology that is less expensive to manufacture, significantly more efficient, and which enables new functionalities and applications far beyond illumination.

At the heart of today’s LED lighting systems are chips made from GaN, a semiconductor material. For the LED to function, many external components - such as inductors, capacitors, silicon interconnects, and wires - must be installed on or integrated into the chip.

The large size of the chip, with all of these necessary components, complicates the design and performance of LED lighting products. Additionally, the process of assembling these complex LED lighting systems can be slow, manually intensive, and expensive.

In a new study led by T. Paul Chow, professor in the Department of Electrical, Computer, and Systems Engineering (ECSE) at Rensselaer, the researchers sought to solve this challenge by developing a chip with components all made from GaN.

This type of monolithically integrated chip simplifies LED device manufacturing, with fewer assembly steps and less required automation. What's more, LED devices made with monolithically integrated chips will have fewer parts to malfunction, higher energy efficiency and cost effectiveness, and greater lighting design flexibility.

Chow and the research team grew a GaN LED structure directly on top of a GaN high-electron-mobility transistor (HEMT) structure. They used several basic techniques to interconnect the two regions, creating what they are calling the first monolithic integration of a HEMT and an LED on the same GaN-based chip.

A cross-section of the new monolithically integrated GaN LED and HEMT

The device, grown on a sapphire substrate, demonstrated light output and light density comparable to standard GaN LED devices. Chow said the study is an important step toward the creation of a new class of optoelectronic device called a light emitting integrated circuit (LEIC).

Monolithically integrated LED and HEMT structure on the same GaN chip. The device is seen here with the LED off (left) and with the LED on (right)

“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.

“This new study, and the device we have created, is just the tip of the iceberg,” adds Smart Lighting ERC Director Robert Karlicek, a co-author of the study and ECSE professor at Rensselaer. “LEICs will result in even higher energy efficiency of LED lighting systems. 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.”

This work is described in detail in the paper, “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,” by Z. Li et al in Applied Physics Letters, 102, 192107 (2013). http://dx.doi.org/10.1063/1.4807125

This research was funded by the National Science Foundation 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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