Diamond semiconductors have emerged as a promising candidate for radio frequency (RF) and microwave devices due to their exceptional material properties. With an ultra-wide bandgap of 5.5 eV, high carrier mobility, and unmatched thermal conductivity, diamond offers significant advantages for high-frequency, high-power applications. The combination of these properties makes it an attractive alternative to gallium nitride (GaN) and silicon carbide (SiC) in RF electronics, particularly for next-generation communication systems, radar, and satellite technologies.

One of the most critical advantages of diamond in RF applications is its high charge carrier velocity. The saturation velocity of electrons in diamond exceeds 2.7 × 10^7 cm/s, which is significantly higher than that of GaN (approximately 2.5 × 10^7 cm/s) and silicon (1 × 10^7 cm/s). This high velocity directly translates into faster switching speeds and higher cutoff frequencies, enabling diamond-based devices to operate efficiently in the millimeter-wave and terahertz regimes. Additionally, the high breakdown electric field of 10 MV/cm allows diamond devices to sustain much higher voltages than GaN or SiC, making them suitable for high-power RF amplification.

Thermal management is another key advantage of diamond in RF electronics. With a thermal conductivity of around 2200 W/m·K—nearly five times that of copper—diamond efficiently dissipates heat generated during high-power operation. This property is crucial for maintaining device performance and reliability, as excessive heat can degrade carrier mobility and increase parasitic resistances. In GaN-based high-electron-mobility transistors (HEMTs), self-heating effects often limit power density, but diamond’s superior thermal conductivity mitigates these issues, allowing for more compact and efficient designs.

Diamond-based HEMTs have been explored as a potential successor to GaN HEMTs in RF power amplifiers. One proposed design involves a hydrogen-terminated diamond (H-diamond) surface with a two-dimensional hole gas (2DHG) channel. The 2DHG forms due to the transfer of electrons from the diamond valence band to surface adsorbates, creating a high-mobility hole channel with sheet carrier densities exceeding 10^13 cm^-2. However, achieving high electron mobility in diamond remains challenging due to the absence of shallow donors. Recent advancements in delta doping and surface passivation techniques have improved carrier transport, but further optimization is needed to compete with GaN’s well-established electron channels.

Another promising RF device is the diamond resonator, which leverages the material’s high acoustic velocity and low mechanical losses for high-frequency signal processing. Bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators made from single-crystal diamond exhibit superior quality factors and frequency stability compared to conventional materials like quartz or lithium niobate. These resonators are particularly useful in filters and oscillators for 5G and beyond, where signal integrity and phase noise are critical.

Despite its advantages, diamond faces several material limitations that hinder its widespread adoption in RF electronics. Trap states at the diamond surface and within the bulk can degrade device performance by increasing scattering and reducing effective carrier mobility. Hydrogen termination helps passivate some of these traps, but interface states between diamond and dielectric layers remain a challenge. Additionally, parasitic resistances in ohmic contacts and access regions can limit high-frequency gain. Palladium and gold-based contacts have shown relatively low specific contact resistance, but further improvements are necessary to minimize losses.

Comparing diamond to GaN in RF applications reveals a nuanced trade-off between performance and technological maturity. GaN HEMTs currently dominate the RF power amplifier market due to their high electron mobility (up to 2000 cm²/V·s in AlGaN/GaN heterostructures) and well-developed fabrication processes. GaN devices achieve cutoff frequencies (f_T) exceeding 100 GHz and maximum oscillation frequencies (f_max) above 200 GHz, making them suitable for X-band and Ka-band applications. Diamond’s theoretical performance exceeds these metrics, but experimental devices have yet to fully realize this potential due to material and fabrication challenges.

In terms of power handling, diamond’s higher breakdown field and thermal conductivity give it an edge over GaN. While GaN can deliver power densities of 5-10 W/mm at microwave frequencies, diamond-based devices could potentially exceed 20 W/mm with proper thermal management. However, GaN benefits from lower defect densities and more mature epitaxial growth techniques, resulting in better reproducibility and yield. Diamond synthesis via chemical vapor deposition (CVD) still faces issues with dislocation densities and impurity incorporation, which can affect device uniformity.

Future advancements in diamond RF technology will depend on overcoming key material and processing hurdles. Improving the quality of epitaxial diamond layers, developing reliable n-type doping methods, and optimizing device architectures are critical steps toward commercialization. Hybrid approaches, such as integrating diamond heat spreaders with GaN transistors, may offer near-term solutions while all-diamond devices continue to mature. As research progresses, diamond’s unique properties could redefine the limits of RF and microwave electronics, enabling new capabilities in high-frequency, high-power systems.

In summary, diamond semiconductors hold immense potential for RF and microwave devices due to their high carrier velocity, thermal conductivity, and breakdown strength. While challenges related to trap states, parasitic resistances, and material quality persist, ongoing research is steadily addressing these limitations. As diamond-based HEMTs and resonators advance, they may eventually surpass GaN in performance, offering a new paradigm for high-frequency electronics. The competition between these materials will drive innovation, with diamond poised to play a pivotal role in the future of RF technology.