Fig. 1. (Color online) The schematic of the grown AlGaN/GaN HEMT structure.

Fig. 2. (Color online) The microscope photograph of the fabricated double-finger GaN HEMT with a L_G of 0.45 µm and total W_G of 200 µm. The pad is designed to be suitable for ground-signal-ground (GSG) probe.

Fig. 3. (Color online) The HRXRD results of the AlGaN/GaN HEMT structure with (a) ω-scan of (0002) and (b) (10-12) diffraction peaks, and (c) ω–2θ scan of (0004) planes.

Fig. 4. (Color online) The results of Non-contact Hall measurements at room temperature with average values of 2DEG (a) mobility and (b) concentration being 2291.1 cm²/(V·s) and 9.954 × 10¹² cm^–2, respectively.

Fig. 5. (Color online) Typical output characteristic (a) I_DS–V_DS and transfer characteristics (b) I_DS–V_GS. In PIV mode, each pulse cycle includes an on-state pulse of 300 µs with a duty cycle of 0.3%.

Fig. 6. (Color online) The extrinsic small signal characteristics of the fabricated AlGaN/GaN HEMT device.

Fig. 7. (Color online) The power performances of the fabricated AlGaN/GaN HEMT device. The measurement was performed under PW-mode with a pulse width of 100 μs and a duty cycle of 1%. The bias was in class-AB operation, under (a) (–3.5, 28) V, (b) (–3.5, 34) V and (c) (–3.5, 40) V gate/drain direct current (DC) bias, respectively.

Fig. 8. (Color online) The obtained P_out, PAE and power gain, depicted as a function of V_DS. During the measurement, the P_in was fixed in 18 dBm, and the V_GS was fixed in –3.5 V.

Fig. 9. (Color online) Pulsed current-voltage characteristics of the device. Measurements are taken under different quiescent bias point (V_GSQ, V_DSQ), as indicated in the graph. Each test pulse period consists of a 1 μs on-state pulse, followed by a 999 μs off-state pulse (0.1% duty cycle). Here V_GS is taken from –6.0 to 2.0 V in steps of 1.0 V.

Table 1. The growth parameters of the AlGaN / GaN HEMT structure.

Table 2. The detailed measurement results of power performances of the fabricated AlGaN/GaN HEMT device.

Table 3. The calculated possible output power and drain efficiency corresponding to different V_DS from 28 to 40 V when V_GS = –3.5 V.