Breakthrough in Chip Technology
Researchers from Cornell University and the Polish Academy of Sciences have teamed up to develop the world’s first chip that seamlessly combines LED and transistor technologies. This innovative Transistor-LED Chip paves the way for smaller, more affordable, and highly efficient LEDs, revolutionizing the possibilities in the field.
Published Research
The team’s paper, titled “Using Polar Semiconductor Wafers in Functional Devices,” was published in Nature on September 25. The principal authors include doctoral students Len van Deurzen and Yingkyun Kim.
Project Leadership
This project was led by Debdeep Jena and William L. Quackenbush, professors in the Electrical and Computer Engineering and Materials Science and Engineering departments at Cornell University.
Technical Details
The researchers constructed gallium nitride (GaN) devices with a high electron mobility transistor (HEMT) on one side and an LED on the other. They leveraged GaN’s unique property of significant electronic polarization along its crystal axis, resulting in different physical and chemical properties on each surface. The gallium side is suited for photonic devices, while the nitrogen side is ideal for transistor applications.
Fabrication Process
The team first grew a transparent GaN substrate (400 micrometers thick) on a single crystal wafer. They then utilized molecular beam epitaxy (MBE) technology to grow HEMT and LED heterostructures. After the devices were transported to Cornell University, Kim constructed and processed the HEMT on the nitrogen side. The final step involved creating the LED on the metal side, using a thick positive photoresist layer to protect the previously processed n-type surface.
GaN stands out among wide bandgap semiconductors due to its large electronic polarization along its crystal axes, allowing for notably different physical and chemical characteristics on each surface. Gallium (the cation) has proven useful for photonic devices such as LEDs and lasers, while nitrogen (the anion) supports transistor functionality.
Unique Achievements
The Jena-Xing lab set out to create a functional device where one side features a high electron mobility transistor (HEMT) driving an LED on the opposite side—a feat not achieved with any material thus far.
“To our knowledge, no one has created active devices on both sides, even with silicon devices,” said van Deurzen. “One reason is that silicon wafers are cubic, meaning there is no added functionality using both sides; they are essentially the same. But GaN is a polar crystal, so one side has different physical and chemical properties than the other, which gives us an extra degree of design flexibility.”
Collaboration and Development
The project was initially conceived by Jena and former postdoctoral researcher Henryk Turski, a co-senior author of the paper. Turski collaborated with a team at the Polish Academy of Sciences‘ High Pressure Research Institute to grow a transparent GaN substrate on the approximately 400-micrometer-thick single crystal wafer.
Following this, the HEMT and LED heterostructures were grown in Poland using molecular beam epitaxy. Once the epitaxy was complete, the chip was sent to Cornell, where Kim worked on the nitrogen side.
Kim noted, “The chemical reactivity on the nitrogen side is higher, which means the electron channel can be easily damaged during device processing. One challenge in manufacturing nitrogen-side transistors is ensuring that all plasma processes and chemical treatments do not damage the transistors. Therefore, a lot of process development is required for transistor manufacturing and design.”
Testing Innovations
Van Deurzen then constructed the LED on the metal side, employing a thick positive photoresist coating to protect the previously processed n-type surface. After each phase, the researchers measured the device characteristics, confirming they remained unchanged.
“This is actually a very viable process,” van Deurzen stated. “The devices do not degrade. This is clearly important if you want to use it as a real technology.”
Given that no one had previously manufactured dual-sided semiconductor devices, the research team had to invent a new method to test and measure it. They assembled a “rough” dual-coated glass plate, connecting one side of the wafer to it to allow detection from the top of both sides.
Due to the transparency of the GaN substrate across the visible spectrum, light can pass through. A single HEMT device successfully drove a large LED, toggling it on and off at kilohertz frequencies—sufficient for a functioning LED display.
Potential Applications
Currently, LED displays operate with separate transistors and distinct manufacturing processes. A direct application of the dual-electronic chip is in Micro LEDs: fewer components, smaller footprint, reduced energy and material requirements, faster production, and lower costs.
“A good analogy is the iPhone,” Jena explained. “Of course, it’s a phone, but it also has many other functions. It’s a calculator, it’s a map, it allows you to browse the internet. There’s a degree of convergence. I would say that what we’ve demonstrated in this paper as ‘dual-electronic’ could merge two or three functionalities, but it’s actually much larger than that.”
“Now, you might not need different processors to perform various functions, reducing energy and speed losses during their interconnection, which typically requires further electronics and logic. Through this demonstration, many of these functionalities are condensed onto a single wafer.”
Other applications include Complementary Metal-Oxide-Semiconductor (CMOS) devices, with one side featuring a polarization-induced n-channel transistor (using electrons) and the other a p-channel transistor (containing holes).
Additionally, due to the high piezoelectric coefficient of the GaN substrate, it could serve as a bulk acoustic wave resonator for RF signal filtering and amplification in 5G and 6G communications. This semiconductor can also utilize lasers instead of LEDs for “LiFi,” or light-based transmissions.
“You can essentially expand it to enable the fusion of photonic, electronic, and acoustic devices,” van Deurzen remarked. “What you can do is fundamentally limited only by your imagination, and as we try them in the future, undiscovered functionalities may emerge.”
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