With the continuous evolution of semiconductor technology, each technological breakthrough, from first-generation silicon (Si) materials to third-generation wide bandgap semiconductors (SiC, GaN), has driven the application of electronic devices in extreme environments such as high frequency, high power, and high temperature. However, third-generation semiconductor materials still have limitations in breakdown field strength, thermal conductivity, and adaptability to extreme conditions, prompting researchers to explore the more promising fourth-generation semiconductor materials. These primarily include ultra-wide bandgap (UWBG) materials such as gallium oxide (Ga₂O₃), diamond, and aluminum nitride (AlN). With wider bandgaps, higher breakdown field strengths, and superior thermal stability, these materials are considered key enablers for next-generation high-power electronics, RF devices, and deep-ultraviolet optoelectronics.

Key Materials and Their Properties

1. Gallium Oxide (Ga₂O₃)

Gallium oxide is an emerging ultra-wide bandgap semiconductor with a bandgap of approximately 4.8-5.3 eV, wider than that of SiC (3.3 eV) and GaN (3.4 eV). This theoretically enables higher breakdown voltages. With a breakdown field strength exceeding 8 MV/cm—20 times that of Si—Ga₂O₃ shows great potential in high-voltage power electronics. Additionally, gallium oxide can be produced using melt growth methods, which yield high-quality single crystals at lower manufacturing costs compared to SiC and GaN epitaxial growth. However, a major challenge is the difficulty in achieving p-type doping, meaning current applications are primarily focused on n-type devices such as Schottky diodes and MOSFETs.

Application Cases:

In 2023, a Japanese research institute successfully developed a 10 kV-class Ga₂O₃ MOSFET with higher power density than SiC devices.

In 2024, a U.S. company developed a Ga₂O₃-based RF power amplifier with excellent performance in millimeter-wave bands, applicable to 6G base stations.

2. Diamond

Diamond is regarded as one of the most outstanding semiconductor materials, featuring a bandgap of 5.5 eV, far exceeding SiC and GaN, along with a breakdown field strength of 10-20 MV/cm. It also has the highest known thermal conductivity (>2000 W/m·K), significantly enhancing device heat dissipation. Diamond's high electron mobility makes it ideal for high-frequency, high-power electronic applications. Current research focuses on high-quality single-crystal growth, n-type doping (such as phosphorus doping), and device fabrication techniques.

Application Cases:

In 2022, a European laboratory successfully developed the first diamond-based RF power amplifier, outperforming existing GaN devices for radar and satellite communications.

In 2023, a Japanese company developed a diamond power diode with exceptional radiation resistance for nuclear industry applications.

3. Aluminum Nitride (AlN)

With a bandgap of approximately 6.2 eV, AlN ranks among the top ultra-wide bandgap semiconductors. It boasts excellent thermal conductivity, high-temperature resistance, and radiation tolerance, making it highly promising for high-frequency RF filters (e.g., 5G/6G), deep-ultraviolet LEDs, and UV lasers. However, the growth of high-quality AlN single crystals remains a challenge due to high defect densities and the need for more advanced epitaxial technologies.

Application Cases:

In 2023, a U.S. laboratory developed an AlN-based deep-ultraviolet LED with 20% efficiency, suitable for high-efficiency sterilization and medical lighting.

In 2024, a Chinese company achieved mass production of AlN RF filters, successfully integrating them into 5G communication systems.

Industry Development and Technological Challenges

In high-voltage power electronics, Ga₂O₃ MOSFETs and Schottky diodes (SBDs) are suitable for power conversion systems exceeding 10 kV, such as power grid converters, electric vehicle charging infrastructure, and railway systems. Diamond power electronics, including FETs and power diodes, hold potential for aerospace, defense, and high-power applications in extreme environments. In high-frequency RF devices, AlN/ScAlN filters are expected to be key for 5G, 6G, and terahertz communications, while Ga₂O₃ RF power amplifiers demonstrate superior performance in millimeter-wave bands. Additionally, AlN deep-ultraviolet LEDs and lasers have broad applications in disinfection, photolithography, and specialized lighting, while Ga₂O₃ ultraviolet detectors hold significant value for solar-blind UV detection, space exploration, and security monitoring.

To advance fourth-generation semiconductor development, challenges in material fabrication and epitaxial technology must be addressed. Ga₂O₃ requires improved p-type doping efficiency and the exploration of heteroepitaxy (e.g., Si/Ga₂O₃, GaN/Ga₂O₃). Diamond requires optimized CVD growth processes to reduce defect densities and improve n-type doping techniques. AlN, on the other hand, needs advancements in PVT and MOCVD methods to produce high-quality single crystals, reduce dislocation densities, and enhance device reliability.

Future Outlook

By 2030, Ga₂O₃ power devices are expected to enter commercial markets, partially replacing SiC/GaN devices. Diamond-based electronic devices are likely to be piloted in high-end markets such as military, aerospace, and nuclear industries. AlN-based deep-ultraviolet LEDs are projected to achieve breakthroughs in sterilization and photolithography applications. With their ultra-wide bandgap properties, fourth-generation semiconductors show great potential in high-power electronics, RF communications, and deep-ultraviolet optoelectronics. While still in the research phase, advancements in material synthesis, device design, and fabrication processes are accelerating commercialization. In the future, fourth-generation semiconductors are poised to drive a new technological revolution in the semiconductor industry, opening up broader application possibilities for high-performance electronic devices.