Characteristic comparison of AlGaN/GaN enhancement-mode HEMTs with CHF ₃ and CF₄ surface treatment

In this study, enhancement-mode (E-mode) AlGaN/GaN HEMTs that underwent CHF₃ and CF₄ plasma treatment beneath the gate metal were fabricated. These treatments were applied because, although previous studies have formed AlF₃ compound layers after fluorine-based plasma treatment to suppress the polarization-induced charge density, the surface negative charges still influenced the device gate leakage current and trap density. In the device in this study, unlike in previous CF₄ plasma-treated GaN E-mode devices, the hydrogen atoms of the CHF₃ plasma were introduced to compensate for vacancies by donating an electron to a vacancy acceptor level, thereby reducing the number of vacancy induced traps. Based on the measured subthreshold slope (SS) and the effective interface state density (D_it) results, the SS value of a CHF₃-treated HEMT was 80 mV/decade and the D_it was 1.23 × 10¹² cm^-2. Moreover, the CHF₃-treated HEMT exhibited a current gain cut-off frequency, a maximum oscillation frequency, and an output power of 6.7, 26, and 14.8 dBm (302 mW/mm), respectively. The 1/f noise measurement results of the CHF₃-treated HEMT indicated that the flicker noise-induced generation-recombination noise and gate leakage-induced generation-recombination noise were also improved. Therefore, the CHF ₃-treated HEMT has great potential for use in low-distortion power amplifiers and logic control circuits.