Fig. 1. (Color online) (a) Scanning electron microscope (SEM) image, (b) cross-sectional schematic, and (c) process flow diagram depicting the fabricated E-mode 1-μm gate UTB-AlGaN/GaN HEMTs on a silicon substrate in this study. The device characteristics L_G/W_G/L_GS/L_GD are 1/75/0.3/0.5 μm. (d) A cross-sectional transmission electron microscopy (TEM) image illustrates the UTB-AlGaN/GaN heterostructure. Although there are no observable sharp boundaries among the three layers, the thickness of the different layers is marked according to our design parameters.

Fig. 2. (Color online) The DC I−V features of the E-mode UTB-AlGaN/GaN HEMTs fabricated on a silicon substrate. The device parameters are specified as follows: L_G = 1 μm, W_G = 75 μm, and L_SD = 1.8 μm. (a) Transfer characteristics are depicted under V_DS = 10 V. (b) DC output characteristics are presented. (c) Threshold voltage uniformity is characterized. (d) Gate leakage current is measured under V_DS of 1 and 10 V, respectively.

Fig. 3. (Color online) The off-state breakdown characteristics of the manufactured E-mode UTB-AlGaN/GaN HEMTs on a silicon substrate, with measurements conducted at V_GS = −1 V. The device dimensions are as follows: L_G = 1 μm, W_G = 75 μm, and L_SD = 1.8 μm.

Fig. 4. (Color online) (a) Radio frequency properties of the produced E-mode UTB-AlGaN/GaN HEMTs under V_DS = 10 V and V_GS = 1.8 V. The device is characterized with L_G/W_G/L_GS/L_GD = 1/75/0.3/0.5 μm. (b) Variation of the f_T/f_MAX and gain at 3.5 GHz with V_GS.

Fig. 5. (Color online) The pulse current−voltage (I−V) characteristics of the manufactured E-mode UTB-AlGaN/GaN HEMTs. (b) A schematic waveform depicts the gate and drain bias variations during the pulsed I−V measurement. (c) and (d) Continuous wave power performance is presented at 3.5 GHz for the fabricated E-mode UTB-AlGaN/GaN HEMTs, showcasing different variations in V_GS and V_DS respectively. The device features dimensions L_G/W_G/L_GS/L_GD is 1/75/0.3/0.5 μm.