In an exciting development in the world of electronics, researchers have designed a new type of transistor that could drastically change how our future devices operate. This invention, called a “hot-emitter transistor,” could help power next-generation technologies that demand both speed and energy efficiency, such as advanced communication systems and high-performance computers. The research, published in Nature, introduces a novel way to boost performance by tapping into the energy of high-speed, or “hot,” carriers electrons and holes that carry electric current.
Traditionally, transistors are the fundamental building blocks of electronics, which work by controlling the flow of electrons through a material. They are used in nearly every modern device, from smartphones to computers. But as we push the limits of what current technologies can do, researchers are constantly seeking ways to make transistors faster, more efficient, and more versatile. This is where the new hot-emitter transistor steps in.
Chi Liu, one of the leading authors of the study, explained the importance of this breakthrough: “Our hot-emitter transistor offers a fresh approach to transistor design, using heated carriers to achieve speeds and efficiencies beyond what traditional designs can provide.” This concept may sound technical, but it’s grounded in a simple idea, which is that when carriers like electrons are “heated” or given extra energy, they can move faster, leading to quicker device operation.
Image of the hot-emitter transistor structure. Credit: Chi Liu et al., “A hot-emitter transistor based on stimulated emission of heated carriers,” Nature, 2024.
The hot-emitter transistor operates differently from conventional transistors by taking advantage of what’s known as “stimulated emission of heated carriers.” To break that down in everyday language, imagine that you have particles (electrons or holes) moving through the material. By giving them an extra energy boost (akin to heating them), these particles move faster and more efficiently. What makes this new transistor special is that it manages to control this flow of high-energy particles in a way that results in better performance and lower power consumption.
One of the most impressive aspects of this invention is its subthreshold swing. Subthreshold swing is a fancy term for how well a transistor can switch on and off. For transistors, being able to switch with less energy is key to making devices more power-efficient. Traditional transistors face a physical limit that makes it hard to improve this ability without sacrificing performance. However, the hot-emitter transistor has shattered this barrier. According to the research, this new design achieves a subthreshold swing of less than 1 millivolt per decade, a significant improvement over conventional designs that usually sit around 60 millivolts per decade. In simpler terms, the new transistor switches on and off with an incredibly tiny amount of energy, making it far more efficient than anything we’ve seen before.
The characteristics and mechanisms of the hot-emitter transistor. The graphs (a-g) illustrate the device’s performance under various conditions, showing data on subthreshold swing (SS), critical base voltage, and current flow. The diagrams (h and i) offer a visual representation of the device structure and the stimulated emission of heated carrier (SEHC) mechanism, explaining how carriers move through the transistor and contribute to its unique performance.
Credit: Image from Chi Liu et al., “A hot-emitter transistor based on stimulated emission of heated carriers,” Nature, 2024.
Another standout feature is the transistor’s ability to display what is called “negative differential resistance” (NDR). Normally, as you increase the voltage in a transistor, the current also increases. But in the hot-emitter transistor, after a certain point, increasing the voltage actually causes the current to decrease. This unusual behavior, known as NDR, is highly desirable for specific applications like high-frequency oscillators and amplifiers, which are essential components in advanced communication technologies.
This image shows detailed graphs representing the performance of the hot-emitter transistor, particularly focusing on its negative differential resistance (NDR). Graphs (a-d) illustrate how the current behaves with changes in voltage and temperature, showing both the peak current and the peak-to-valley ratio (PVR) at different conditions. The scatter plot (e) compares the PVR performance of this new device with previous devices made using various materials, highlighting the superior performance of the hot-emitter transistor.
Credit: Image from Chi Liu et al., “A hot-emitter transistor based on stimulated emission of heated carriers,” Nature, 2024.
“By achieving a peak-to-valley current ratio of over 100 at room temperature, we have demonstrated a major leap in NDR performance,” said Liu. This is especially important because it shows that the device works well under normal conditions (at room temperature) without requiring complex cooling systems.
What’s particularly exciting is the potential real-world applications of this technology. As the demand for faster, smaller, and more energy-efficient devices grows, innovations like the hot-emitter transistor could play a crucial role in shaping the future of electronics. One area where this could make a big impact is in the development of 6G technology. As we move beyond 5G, the next generation of wireless communication will require devices that can process huge amounts of data at lightning speed. The unique properties of the hot-emitter transistor make it an ideal candidate for such high-speed, high-frequency applications.
The researchers also highlighted the possibility of using this technology for multi-valued logic systems, which could revolutionize how computers process information. Today’s computers rely on binary logic, which is everything either a 0 or a 1. But multi-valued logic systems allow for more states, which means more information can be processed at once. The hot-emitter transistor has demonstrated the ability to support such systems, which could lead to faster, more powerful computers that use less energy.
Despite these promising results, the research team acknowledges that there are still challenges to overcome before the hot-emitter transistor can be widely adopted. One of the main hurdles is improving the consistency and reliability of the device. Currently, the technology shows some variability in performance, which would need to be refined for large-scale production. However, the team remains optimistic.
“Innovation like this takes time,” said Dong-Ming Sun, another senior author of the paper. “But with continued research and development, we believe this technology has the potential to become a game-changer for the electronics industry.”
Looking ahead, the researchers plan to explore other materials that could further enhance the performance of the hot-emitter transistor. For example, pairing graphene with other semiconductors may unlock even greater efficiencies. They also hope to reduce the device’s hysteresis, which is the lag between switching on and off, leading to improved precision.
Citation: Liu, C., Wang, X.-Z., Shen, C., Ma, L.-P., Yang, X.-Q., Kong, Y., Ma, W., Liang, Y., Feng, S., Wang, X.-Y., Wei, Y.-N., Zhu, X., Li, B., Li, C.-Z., Dong, S.-C., Zhang, L.-N., Ren, W.-C., Sun, D.-M., & Cheng, H.-M. (2024). A hot-emitter transistor based on stimulated emission of heated carriers. Nature, 632, 782–787. https://doi.org/10.1038/s41586-024-07785-3
