Future global communication networks that also cover remote regions, withstand potential sources of interference, and can step in during disasters, must be able to reliably process high data rates. High-throughput satellites (HTS) in low Earth orbit (LEO) and/or geostationary orbit (GEO), which use the broadband Ka-, Q-, and W-frequency bands and follow strict modulation schemes, offer a promising option for implementing such networks. The hardware required for such communication systems, active antennas for electronic beam steering, relies on extremely efficient power amplifiers with high linearity. 

The compactness required for active antennas causes thermal problems with existing components. Researchers at the Fraunhofer Institute for Applied Solid State Physics IAF have therefore developed high electron mobility transistors (HEMTs) based on the wide bandgap compound semiconductor gallium nitride (GaN), which have a gate length of only 70 nm. The measured efficiency values demonstrate the great potential of this innovative technology for future applications in satellite communications.

Components for broadband satellite communication

“Thanks to their high linearity and efficiency, the GaN power amplifier HEMTs developed at Fraunhofer IAF enable more compact and energy-efficient communication systems for satellites. With our innovative technology, we are making an important contribution to the establishment and expansion of seamless and resilient global communication networks,” explains Dr. Philipp Döring, scientist in the Technology Department at Fraunhofer IAF and lead author of the research paper presenting the 70 nm GaN HEMTs.

Dr. Döring will present the paper “High efficiency and high linearity 70 nm GaN technology for future SatCom applications” on September 23 from 2:10 p.m. to 2:30 p.m. at the European Microwave Integrated Circuits Conference (EuMIC) in Utrecht, Netherlands. EuMIC is part of European Microwave Week (EuMW).

70 nm GaN transistors with record efficiency

The GaN HEMTs were developed, manufactured, and characterized in the in-house semiconductor line in the Epitaxy, Technology, and Microelectronics departments at Fraunhofer IAF. The GaN/AlGaN (aluminum gallium nitride) semiconductor material system was grown on semi-insulating 4-inch silicon carbide (SiC) substrates using metal organic chemical vapor deposition (MOCVD). Processing was carried out using electron beam lithography, among other methods. 
The researchers performed test measurements on individual transistors as well as directly on the wafer. In small-signal measurements, a cut-off frequency of fT = 122/95 GHz and a maximum frequency of fMAX more than 350 GHz were determined at VDS of 7/15 V. Load-pull measurements yielded a maximum power-added efficiency of 58.6% and a maximum output power of 2.46 W/mm at 38 GHz on 8×60 µm transistors.
To determine signal linearity, the researchers used a two-tone load pull method to test which of the 70 nm GaN HEMT meet the requirements currently specified by the European Space Agency (ESA) for satellite communications. Under the boundary condition of IMD3 ≥ 30 dBC, the technology achieved an efficiency of PAE = 54.4% and an output power of 1.01 W/mm. This is the highest efficiency value ever measured for a GaN technology at 30 GHz.

Technology development in the context of the Magellan and GANYDEM170 projects
The results were obtained as part of the Magellan and GANYDEM170 projects. Magellan is funded by ESA and aims to develop highly efficient millimeter-wave GaN high-power amplifiers for GEO and LEO active antenna applications. GANYDEM170 is funded as an IPCEI (Important Project of Common European Interest) by the German Federal Ministry for Economic Affairs and Energy (BMWE) and enables the realization of an industry-ready millimeter-wave GaN technology for metrology applications.

Fraunhofer IAF at EuMW 2025

At EuMW 2025, which will take place from September 21 to 26 in Utrecht, Netherlands, Fraunhofer IAF will present further research results from the field of GaN-based high-frequency electronics in addition to the findings of Dr. Philipp Döring. On the one hand, the institute will exhibit a wide selection of components, circuits, and modules at booth B071 at the trade fair. On the other hand, Patrick Umbach, Thomas Zieciak, Moïse Safari Mugisho, and Dr. Philipp Neininger will give presentations at EuMIC. In addition, the institute’s director, Dr. Patricie Merkert, will participate in the EuMIC Foundry Panel, where she will talk about monolithic and heterogeneous integration as well as chiplets.

Overview of all presentations by Fraunhofer IAF

EuMIC04-5 – Monday, September 22, 12:10–12:30
Patrick Umbach: Monolithic Integrated Broadband IF Balun and LO Amplifier

EuMIC06-4 – Monday, September 22, 14:50–15:10
Thomas Zieciak: A 200 mW, high-gain GaN-based D-Band Power Amplifier for 6G Communication Applications

EuMIC10 – Monday, September 22, 16:10–17:50
EuMIC Foundry Panel mit u. a. Dr. Patricie Merkert 

EuMIC11-5 – Tuesday, September 23, 9:50–10:10
Moïse Safari Mugisho: A V-Band (61–72 GHz) GaN HEMT High-Power Amplifier

EuMIC14-2 – Tuesday, September 23, 14:10–14:30
Dr. Philipp Döring: High efficiency and high linearity 70 nm GaN technology for future SatCom applications

EuMIC/EuMC03 – Halle 7 | 1-Minute Poster Pitch – Media Arena, 9:30–10:10
Dr. Philipp Neininger: An Integrated W-Band Dual-Polarization Receiver Front-End Featuring Ultra-Low Noise Figure
 

The team’s discovery centers around the compound MnBi₆Te₁₀, a complex topological material notable for its unique electronic traits, including the ability to conduct electrical current along its edges without resistance, a phenomenon tied to its topological protection. Such materials are at the forefront of quantum research because of their promise to underpin future quantum computing hardware and innovative electronic devices with unprecedented efficiency. However, the findings reveal layers of complexity in their electron distribution that were previously unappreciated.

Under standard assumptions, the electronic charges in MnBi₆Te₁₀ would be uniformly distributed across the crystal layers to sustain stable quantum properties. To verify this, the research team introduced antimony doping, adjusting the compound’s chemical composition judiciously to balance the charge. Common electrical testing techniques initially confirmed an overall neutral charge state. But upon deploying advanced spectroscopic tools, a different reality emerged beneath the surface of the material’s structure.

Utilizing an advanced method known as time- and angle-resolved photoemission spectroscopy (trARPES), the researchers could track electron behavior with ultrafast laser pulses, observing where the electrons resided and how their energy states fluctuated in real-time. What they uncovered challenged earlier assumptions: within each crystalline unit, electrons exhibited an uneven distribution, clustering in certain atomic layers while depleting in others. This micro-scale charge sorting gave rise to distinct, nano-sized built-in electric fields embedded in the crystal.

Such an intra-unit-cell charge rearrangement forms a natural p-n junction within the quantum material. P-n junctions are semiconductor interfaces critical to electronic functionality, sharply defining regions of positive and negative charge to control current flow and build devices like diodes and transistors. Traditional p-n junctions are engineered manually during semiconductor fabrication, but in this groundbreaking work, the junction emerges spontaneously through the material’s intrinsic properties, heralding a new paradigm where crystal chemistry inherently dictates device-like behavior.

This discovery not only uncovers a naturally occurring p-n junction at an unprecedentedly thin scale but also introduces dynamic, optoelectronic capabilities. The junction exhibits heightened sensitivity to light, indicating its potential to be integrated into spintronics—an emergent field that manipulates electron spin states rather than charge. Spintronic devices promise revolutionary advances in data storage and processing speeds, and the natural p-n junctions could provide versatile platforms to engineer these quantum features at scales previously unattainable.

To unravel the mechanism behind this phenomenon, the researchers modeled the atomic-scale interactions within the MnBi₆Te₁₀ lattice, proposing that antimony substitution disrupts atomic ordering by swapping with manganese atoms. This atomic interchange introduces subtle charge imbalances, cascading through the crystal structure to produce segregated electron pockets. Consequently, what was believed to be a uniform electronic environment proves to be a carefully orchestrated mosaic of charge landscapes, each contributing internal electric fields critical for device-like functions.

While introducing complexity to MnBi₆Te₁₀’s anticipated quantum behavior, this intrinsic charge redistribution opens fresh avenues for technological exploitation. By embracing this natural heterogeneity, scientists can reimagine how to harness these materials for next-generation electronics. Moreover, it suggests strategies for tuning or even designing new topological materials with engineered charge landscapes to optimize performance for quantum and classical applications alike.

Moving forward, the team plans to refine the fabrication of MnBi₆Te₁₀ in thin-film form rather than bulk crystals. Such ultrathin films will offer enhanced control over electron behavior and junction formation, potentially enabling the scalable manufacture of devices where quantum phenomena and semiconductor functionality coexist harmoniously. This fine-tuning approach could accelerate the transition of these scientific breakthroughs from experimental demonstration to practical technology.

Beyond practical tech implications, this discovery highlights the invaluable role of fundamental research aimed at understanding basic material behavior at atomic scales. The serendipitous finding underscores how exploration without a predetermined goal can lead to unanticipated and transformative insights that challenge existing paradigms and inspire fresh directions in science and technology development.

As Asst. Prof. Shuolong Yang emphasized, their journey began with conventional goals but culminated in an unexpected revelation that may ultimately redefine strategies in quantum materials engineering and electronics miniaturization. The natural formation of one of the thinnest known semiconductor junctions within a topological insulator accentuates nature’s intricate design and offers a promising platform for revolutionary device concepts.

The research, published in the journal Nanoscale, stems from a collaborative effort that bridges the expertise of quantum physics, materials science, and electronic engineering. Supported by the U.S. Department of Energy and the National Science Foundation, it situates itself at the frontier where theoretical insight meets experimental innovation, propelling the quest to decode and harness the subtle electronic complexities of quantum materials.

In sum, this unexpected revelation of nanoscale p-n junctions forming spontaneously inside MnBi₆Te₁₀ elevates our understanding of quantum materials and demonstrates the extraordinary potential for integrating these properties into future quantum devices and ultraminiaturized electronics. It invites a re-examination of how intrinsic material properties can be tuned or engineered to foster disruptive technologies, spotlighting both the surprises held within the microcosm of atomic lattices and the strides achievable through cross-disciplinary scientific collaboration.

Subject of Research: Semiconductor junctions, topological quantum materials, intra-unit-cell charge redistribution

Article Title: Spectroscopic evidence of intra-unit-cell charge redistribution in a charge-neutral magnetic topological insulator

News Publication Date: 2-Apr-2025

Web References: https://doi.org/10.1039/d4nr04812a

References: Nguyen et al., Nanoscale, April 2, 2025, DOI: 10.1039/d4nr04812a

Image Credits: John Zich

Keywords: Semiconductors, Materials science, Quantum computing, Quantum information, Electrons, Spintronics