There are two sides to this semiconductor, and many simultaneous functions

ITHACA, N.Y. – Cornell University researchers have helped develop the first dual-sided – or “dualtronic” – chip that combines its photonic and electronic functions simultaneously, an innovation that could shrink the size of functional devices, make them more energy efficient and reduce manufacturing costs.

The team’s paper, “Leveraging Both Faces of Polar Semiconductor Wafers for Functional Devices,” published Sept. 25 in Nature. The co-lead authors are doctoral students Len van Deurzen and Eungkyun Kim. The project was led by Debdeep Jena, professor of engineering, and Huili Grace Xing, professor of electrical and computer engineering.

Gallium nitride (GaN) is unique among wide-bandgap semiconductors because it has a large electronic polarization along its crystal axis, which gives each of its surfaces dramatically different physical and chemical properties. The gallium, or cation, side has proved useful for photonic devices such as LEDs and lasers, while the nitrogen, or anion, side can host transistors.

The Jena-Xing Laboratory made a functional device in which a high electron mobility transistor (HEMT) on one side drives light-emitting diodes (LEDs) on the other – a feat that hasn’t been achieved in any material.

“To our knowledge, nobody has made active devices on both sides, not even for silicon,” van Deurzen said. “One of the reasons is that there’s no additional functionality you get from using both sides of a silicon wafer because it’s cubic; both sides are basically the same. But gallium nitride is a polar crystal, so one side has different physical and chemical properties than the other, which gives us extra degree in designing devices.”

Currently, LED displays have a separate transistor and independent fabrication processes. An immediate application for the dualtronic chip is microLEDs: fewer components, occupying a smaller footprint and requiring less energy and materials, and manufactured quicker for lower cost. 

“A good analogy is the iPhone,” Jena said. “It is, of course, a phone, but it is so many other things. It’s a calculator, it’s a map, it lets you check the internet. So there’s a bit of a convergence aspect of it. I would say our first demonstration of ‘dualtronics’ in this paper is convergence of maybe two or three functionalities, but really it’s bigger than that. Now you may not require the different processors to perform different functions, and reduce the energy and speed lost in the interconnections between them that requires further electronics and logic. Many of those functionalities shrink into one wafer with this demonstration.”

In addition, because the GaN substrates have a high piezoelectric coefficient, they can be used as bulk acoustic wave resonators for filtering and amplifying radio frequency signals in 5G and 6G communications. The semiconductors could also incorporate lasers instead of LEDs for “LiFi” – i.e., light-based – transmissions.

“You could essentially extend this to enable the convergence of photonic, electronic and acoustic devices,” van Deurzen said. “You’re essentially limited by your imagination in terms of what you could do, and unexplored functionalities can emerge when we try them in the future.”

For additional information, read this Cornell Chronicle story.

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