High RF Performance Enhancement-Mode Thin-Barrier AlGaN/GaN HEMTs on Si Substrate for Low-Voltage Applications

In this work, high-performance enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) on Si substrate for low-voltage RF applications were demonstrated. The thin-barrier AlGaN (7 nm) and CF4-based gate recess etching were adopted to realize a positive threshold voltage of 0.13 V. Attributing to the SiN strain layer grown by low-pressure chemical vapor deposition (LPCVD), the sheet resistance of the thin-barrier AlGaN/GaN heterostructure was reduced from 410 to $280~\Omega $ /sq. Hence, the fabricated E-mode thin-barrier AlGaN/GaN HEMTs with regrown ohmic contacts and a small source-drain distance of 850 nm exhibit a high maximum output current of ~1.4 A/mm, a low on-resistance of $0.5~\Omega \cdot $ mm, and a low knee voltage of 1.3 V. Pulsed I–V measurement shows that a low current collapse at 20 V drain quiescent condition of 2.1% was achieved. The continuous wave power measurement of the E-mode devices at 3.6 GHz shows a very large peak power added efficiency (PAE) over 65% with drain voltage ${V}_{\text {ds}}$ from 6 to 12 V (peak PAE of 67.21% at ${V}_{\text {ds}}=6$ V), a high maximum output power density (3.18 W/mm at 12 V), and a linear gain (17.4 dB at 6 V and 21.09 dB at 12 V). These excellent results show that the transistor maintains a constant high PAE and linearly increased gain and output power over the drain voltage variation range, which has great potential and advantages for low-voltage applications.