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Analysis and comparison of GaN-based microwave semiconductor devices
Gallium nitride (GaN), a wide bandgap semiconductor, has emerged as a promising alternative to traditional materials like silicon (Si) and compound semiconductors such as gallium arsenide (GaAs) and gallium phosphide (GaP). As the third-generation semiconductor material, GaN has rapidly gained attention due to its superior physical and chemical properties. Compared to conventional semiconductors, GaN offers a wider bandgap, higher saturation drift velocity, greater breakdown electric field, and better thermal conductivity, making it an ideal candidate for advanced electronic applications.
In recent years, significant progress has been made in GaN-based light-emitting devices. Commercially available GaN LEDs operating in the green-to-violet range have already been developed abroad, while domestic research institutions have successfully produced blue LEDs that are now being industrialized. Additionally, numerous studies highlight the advantages of GaN in high-temperature and high-power microwave device fabrication. This paper explores the material characteristics of GaN, analyzes its suitability for microwave devices, and discusses the latest developments in GaN-based microwave technologies, particularly focusing on modulated doped field effect transistors (MODFETs).
From a material perspective, GaN exhibits remarkable properties that make it highly suitable for high-power microwave applications. Table 1 compares key material parameters of GaN with those of Si, GaAs, and SiC. It clearly shows that GaN has the largest bandgap, the highest breakdown electric field, and better thermal conductivity than other materials, which gives it a clear advantage in high-power applications.
Figure 1 illustrates the relationship between electron drift velocity and electric field at 300 K for GaN, Si, SiC, and GaAs. The data reveals that GaN has a significantly higher saturation drift velocity, making it ideal for high-current and high-power devices. Moreover, GaN has a high electron mobility (up to 1,000 cm²/(V·s) in bulk form), resulting in lower parasitic resistance and improved device performance. As a direct bandgap material, GaN can form AlGaN/GaN heterostructures, enabling the formation of two-dimensional electron gas (2DEG), which enhances electron mobility and drift velocity.
Table 2 compares key parameters of AlGaN/GaN and AlGaAs/GaAs heterojunctions. The results show that AlGaN/GaN structures offer significant material advantages, especially in terms of electron mobility and charge density. For example, researchers at Xi'an University of Electronic Science and Technology have grown high-quality AlGaN/GaN heterostructures on sapphire and SiC substrates, achieving a product of 2×10¹ⶠcmâ»Â²Â·Vâ»Â¹Â·sâ»Â¹ for 2DEG mobility and surface charge density.
Currently, various GaN-based microwave devices, such as MESFETs, HFETs, MODFETs, and MISFETs, are being developed. These devices benefit from GaN’s low heat generation and high breakdown field, making them suitable for high-power microwave applications. Among these, GaN MESFETs have shown great potential in microwave power amplification. Early GaN MESFETs, such as those developed by Khan et al. in 1993, demonstrated good performance with a gate length of 1 μm and a transconductance of 23 mS/mm. Subsequent improvements by SCBinari et al. led to devices with higher cutoff frequencies and better microwave performance, with predictions of output power exceeding 1 W/mm under optimized conditions.
Overall, GaN continues to be a key material in the development of next-generation microwave and power electronics, offering unique advantages that make it a strong contender for future high-performance applications.