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Gallium Nitride (GaN) high-electron mobility transistors (HEMTs) are highly promising for high-frequency and high-power applications due to their superior properties, such as a wide energy bandgap and high carrier density. The performance of GaN HEMTs is significantly influenced by the interfacial states of the AlGaN barrier, and gate annealing has emerged as a key process for reducing leakage currents and enhancing DC/RF characteristics. This research investigates the impact of gate annealing on AlGaN/GaN HEMTs, focusing on two main aspects: leakage current reduction and improvements in DC and RF efficiency. Through comprehensive electrical analysis, including DC and RF measurements, the effects of gate annealing were experimentally evaluated. The results show a significant reduction in gate leakage current and noticeable improvements in DC/RF performance for the devices that underwent gate annealing. The study confirms that the annealing process can effectively enhance device performance by modifying the material properties at the gate interface. [ABSTRACT FROM AUTHOR]

Metal–semiconductor–metal (MSM) varactor diodes are integrated with a THz fishnet metamaterial with its resonance frequency in the terahertz (THz) frequency range. The electrically tunable capacitance enabled by MSM varactor diodes can shift the resonance frequency of the THz fishnet metamaterial and modulate the amplitude of transmitted THz waves. Conventional MSM varactor diodes can be represented by an equivalent circuit consisting of the series‐connected resistance and capacitance. When the frequency increases, the kinetic inductance associated with the two‐dimensional electron gas (2DEG) becomes significant in the THz frequency range. A very large resonance frequency shift as large as 0.57 THz is obtained due to the effect of the kinetic inductance change as well as the capacitance change in the THz metamaterial based on the fishnet structures. The fabricated THz fishnet metamaterial integrated with the MSM‐2DEG varactor diodes exhibits a modulation depth of 54.7% and an insertion loss of 3.32 dB at 0.66 THz. [ABSTRACT FROM AUTHOR]

A large aperture photoconductive antenna (PCA) with a plasmonic grating structure was fabricated and characterized. The intensity of the terahertz radiation from the plasmonic PCA was enhanced two‐fold compared with that from the conventional PCA without the plasmonic grating structure. By using an electrically isolated nano‐grating structure, the performance enhancement was found to be due to the plasmonic effect other than bias field enhancement. The photo‐absorption enhancement near the GaAs surface and the plasmonic grating interface was investigated to elucidate the terahertz radiation enhancement mechanism in the plasmonic PCA. The highly localized electric field near the nanoscale grating shows optical absorption at the GaAs surface was enhanced. The enhanced optical absorption increased the photo‐generated carrier density at the device surface, leading to enhanced intensity and bandwidth of the terahertz radiation from the plasmonic PCA. [ABSTRACT FROM AUTHOR]