Progresses and Frontiers in Ultrawide Bandgap Semiconductors

Abstract

The field of ultra-wide bandgap (UWBG) semiconductors is experiencing a transformative era, driven by the relentless pursuit of materials and technologies that promise to revolutionize power electronics, optoelectronics, and beyond. This special issue brings together a collection of pioneering review and research articles that highlight the latest advancements and future directions in UWB semiconductor technology.

The articles compiled in this issue underscore the remarkable potential of UWBG semiconductors to address critical challenges in materials science and device engineering. From deep ultraviolet optoelectronics to high-temperature electronic applications, the research demonstrates the versatility and unprecedented performance characteristics of these advanced materials. The diversity of approaches represented here is also striking. Researchers have explored multiple material systems—including AlGaN, Ga2O3, and novel oxide semiconductors—each offering unique capabilities that extend the boundaries of traditional semiconductor technologies. The breadth of investigations ranges from fundamental material characterization to device engineering, reflecting the interdisciplinary nature of modern materials research.

In “Thermal Stability of Schottky Contacts and Rearrangement of Defects in β-Ga2O3 Crystals” (aelm.202300428), P. Seyidov and co-authors investigate the thermal stability of Schottky contacts (Au, Pt, Ni) on β-Ga2O3 single crystals. The study reveals critical insights into defect levels and material behavior under thermal stress, identifying defect levels and discussing the rearrangement and dissociation of hydrogen in Ga-O divacancy complexes. These findings are essential for understanding the reliability and performance of β-Ga2O3-based devices under high-temperature conditions.

In “Discovery of a Robust p-type Ultrawide Bandgap Oxide Semiconductor: LiGa5O8” (aelm.202300550), H. Zhao and co-authors introduce a novel p-type UWBG oxide semiconductor with a bandgap of ≈5.36 eV. Utilizing mist-chemical vapor deposition (M-CVD), the study demonstrates robust p-type conductivity with a wide range of hole concentrations. This discovery opens new avenues for creating efficient and robust electronic and optoelectronic devices.

In “Wide-Bandgap Nickel Oxide with Tunable Acceptor Concentration for Multidimensional Power Devices” (aelm.202300662), Y. Zhang and co-authors explore the modulation of acceptor concentration (NA) in NiO by controlling the oxygen partial pressure during magnetron sputtering. The study reveals a tunable acceptor concentration, with practical breakdown fields (EB) ranging from 3.8 to 6.3 MV cm⁻¹. These findings highlight the potential of NiO as a p-type material for power devices, enabling performance beyond conventional limits.

In “Material Properties of n-type β-Ga2O3 Epilayers with In-Situ Doping Grown on Sapphire by Metalorganic Chemical Vapor Deposition” (aelm.202300679), R. Horng and co-authors provide valuable insights into the electrical properties and doping efficiency of these materials. The research underscores the importance of optimizing growth conditions to enhance dopant activation and carrier mobility.

In “Semiconductor Membrane Exfoliation: Technology and Application” (aelm.202300832), B. Ooi and co-authors give a review of various techniques for the exfoliation and transfer of semiconductor membranes, including chemical exfoliation, laser lift-off, mesoporous-layer-assisted exfoliation, and 2D material-assisted exfoliation. These methods present new possibilities for flexible optoelectronic devices and offer innovative pathways for integrating high-performance materials into diverse applications.

In “Progress in Performance of AlGaN-based Ultraviolet Light Emitting Diodes”(aelm.202300840), F. Xu and co-authors review challenges and progress in electrical injection, electro-optical conversion, and light extraction in AlGaN-based UV-LEDs. The papers highlights strategies to enhance carrier injection efficiency and reduce contact resistivity, paving the way for more efficient and reliable UV-LEDs for applications ranging from sterilization to high-density data storage.

In “Recent Advanced Ultra-Wide Bandgap β-Ga2O3 Material and Device Technologies” (aelm.202300844), H. Zhou and co-authors provide a comprehensive review of β-Ga2O3 thin films and devices, covering various growth techniques, including MBE, MOCVD, HVPE, PLD, and Mist-CVD. The article emphasizes the importance of interface quality and power device fabrication, providing a roadmap for future research and development in this promising material system.

In “Lossless Phonon Transition through Interfaces with Diamond” (aelm.202400146), S. Chowdhury and co-authors study the integration of diamond as a heat spreader in 3D ICs and GaN power amplifiers, highlighting the potential of diamond to significantly reduce thermal boundary resistance (TBR) with interlayers such as SiO2, a-SiC, and SiNx. This research is crucial for developing high-power devices with improved thermal management and reliability.

In “Al-rich AlGaN Channel High Electron Mobility Transistors on Silicon: A Relevant Approach for High Temperature Stability of Electron Mobility” (aelm.202400069), J. Bassaler and co-authors investigate AlGaN channel heterostructures on silicon, examining electron mobility and temperature stability. The study explores the impact of Al composition in various layers on device performance, providing insights into optimizing heterostructures for high-temperature applications.

In “Rhodium-Alloyed Beta Gallium Oxide Materials: New Type Ternary Ultra-Wide Bandgap Semiconductors” (aelm.202400547), D. Zhang and co-authors introduce a new class of ternary UWBG semiconductors with enhanced valence band maximum and reduced hole mass. These materials show promise for high-power electronic devices, offering improved performance and efficiency.

In “Out-diffusion and Uphill-diffusion of Mg in Czochralski-grown (100) β-Ga2O3 under High-temperature Annealing and Its Influence on Lateral MOSFET Devices” (aelm.202400342), A. Popp and co-authors study Mg-doped β-Ga2O3 films, investigating the effects of annealing on Mg diffusion and its impact on device performance. The research demonstrates that controlled Mg doping and annealing processes can significantly enhance the performance of power devices.

In “Unraveling Abnormal Thermal Quenching of Sub-gap Emission in β-Ga2O3” (aelm.202400315), J. Ye and co-authors explore the electronic properties of β-Ga2O3, including relaxation and spin polarization, providing a deeper understanding of bandgap calculation and carrier mass analysis. These insights are essential for designing devices with optimized electronic properties.

In “Machine Learning Enabled High-Throughput Screening of 2D Ultrawide Bandgap Semiconductors for Flexible Resistive Materials” (aelm.202400435), C. Chen and co-authors use machine-learning assisted first-principles modeling to predict the electronic properties of a large number of 2D ultra-wide bandgap semiconductors. Studies like this could be the seed for future research in the coming decades.

In “In Situ Growth of (−201) Fiber-Textured β-Ga2O₃ Semiconductor Tape for Flexible Thin-Film Transistor” (aelm.202400046), Xiao Tang and co-authors achieve high-temperature in situ growth of Ga2O3 thin films on SiO_x/Al2O_x buffered substrates. This method overcomes the thermal-stability limitations of conventional polymer substrates, resulting in Ga₂O₃ thin films with a preferred (−201) orientation. The transistors exhibit good electrical performance, uniformity, and mechanical robustness, making this technique promising for flexible Ga2O3-based electronic circuits and potentially other high-temperature processed flexible semiconductor devices.

In “Design and Optimization for AlGaN-Based Deep Ultraviolet Fabry–Perot Laser Diodes” (aelm.202400247), Jianyu Yang and co-authors use Technology Computer Aided Design (TCAD) simulations to develop physical models for AlGaN-based deep ultraviolet Fabry–Perot laser diodes (DUV LDs). They find that increasing the Al composition in the p-waveguide and p-type cladding layer shifts the optical field to the n-region, reducing free-carrier absorption in the p-region. However, this must be balanced to avoid decreasing the optical confinement factor and increasing electron leakage. The study suggests that optimizing the Al composition in the p-electron blocking layer can improve both optical and electrical properties of DUV LD.

In “Electronic Properties of Ultra-Wide Bandgap BxAl1−xN Computed from First-Principles Simulations” (aelm.202400549), Cody L. Milne and co-authors predict the electronic properties of ground states of BAlN using first-principles density functional theory and many-body perturbation theory within the GW approximation. They find that BAlN structures are ultra-wide bandgap materials with bandgaps varying linearly from 6.19 eV (wurtzite-phase AlN) to 7.47 eV (w-BN). The study also reveals a direct-to-indirect bandgap crossover near x = 0.25 and larger dielectric constants for BAlN alloys compared to their bulk counterparts, with values up to 12.1 ɛ0. These findings advance the understanding of BAlN properties, aiding their application in next-generation power electronics.

In “Enhanced UV-Visible Rejection Ratio in Metal/BaTiO₃/β-Ga₂O₃ Solar-Blind Photodetectors” (aelm.202400552), N. Wriedt and co-authors investigated the characteristics of Gallium Oxide-based photodetectors. They find that the photodetector gain in these structures can be explained by a positive trapped hole charge that causes enhancement of electron injection due to image force lowering. They also find remarkable improvement in the UV-visible rejection ratio by insertion of a thin high-permittivity BaTiO₃ layer between the metal and the semiconductor. The findings advance the understanding of Gallium Oxide photodetectors, and could enable higher performance photodetectors in the future.

While the research presented here is groundbreaking, it also highlights the ongoing challenges and opportunities in UWBG emiconductors. Issues of material quality, interface engineering, doping control, and thermal management remain critical areas for continued investigation. The ability to manipulate material properties at increasingly sophisticated levels—whether through precise doping techniques, interface engineering, or novel growth methodologies—represents a key frontier in this field. The potential applications are vast, spanning high-power electronics, extreme environment sensors, ultraviolet optoelectronics, and beyond.

The research compiled in this special issue offers a glimpse into the transformative potential of UWBG semiconductors. The interdisciplinary nature of these investigations—bridging materials science, physics, and engineering—underscores the collaborative spirit driving technological innovation. The articles within this issue not only represent individual scientific achievements, but collectively point toward a future where semiconductor technologies can operate in increasingly extreme and unconventional environments. From deep ultraviolet lasers to flexible electronics, from high-temperature stable transistors to novel oxide semiconductors, the horizon of possibilities continues to expand.

We thank the Advanced Electronic Materials Editor-in-Chief Gaia Tomasello for inviting us to co-edit this special issue, and for her continuous support at each stage of the preparation of this issue. We would like to thank all the authors for their contributions.