A novel 4H-SiC MESFET was presented, and its direct current (DC), alternating current (AC) characteristics and power added efficiency (PAE) were studied. The novel structure improves the saturation current (Idsat) and transconductance (gm) by adding a heavily doped region, reduces the gate-source capacitance (Cgs) by adding a lightly doped region and improves the breakdown voltage (Vb) by embedding an insulated region (Si3N4). Compared to the double-recessed (DR) structure, the saturation current, the transconductance, the breakdown voltage, the maximum oscillation frequency (fmax), the maximum power added efficiency and the maximum theoretical output power density (Pmax) of the novel structure is increased by 24%, 21%, 9%, 11%, 14% and 34%, respectively. Therefore, the novel structure has excellent performance and has a broader application prospect than the double recessed structure.

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An improved P-type doped barrier surface AlGaN/GaN high electron mobility transistor with high power-added efficiency (PDBS-HEMT) is proposed in this paper. Through the modelling and simulation of ISE-TCAD and ADS software, the influence of the P-type doped region on the performance parameters is studied, and the power-added efficiency (PAE) obtained and effectively improved is further verified. The drain saturation current and the threshold voltage of PDBS-HEMT has no major change compared with the traditional structure; the peak transconductance decreases slightly, but the breakdown voltage is significantly enhanced. Furthermore, the gate-source capacitance and gate-drain capacitance are reduced by 14.6% and 14.3%, respectively. By simulating the RF output characteristics of the device, the maximum oscillation frequency of the proposed structure is increased from 57 GHz to 63 GHz, and the saturated output power density is 10.9 W/mm, 9.3 W/mm and 6.4 W/mm at the frequency of 600 MHz, 1200 MHz and 2400 MHz, respectively. The highest PAE of 88.4% was obtained at 1200 MHz. The results show that the PDBS structure has an excellent power and efficiency output capability. Through the design of the P-type doped region, the DC and RF parameters and efficiency of the device are balanced, demonstrating the great potential of PDBS structure in high energy efficiency applications.

A novel 4H-SiC metal semiconductor field effect transistor (MESFET) device with double symmetric step buried oxide layer is proposed and the mechanism is studied through TCAD simulation. The step buried oxide layer is mainly to reduce the current leakage to the substrate and improve drain current. At the same time, the presence of the oxide layer changes the electric field distribution, reduces the electric field concentration phenomenon, and the breakdown voltage is improved. Due to the presence of the step buried oxide layer, the charge distribution of the device is changed, and the frequency characteristics are improved. When the step buried oxide channel is under the optimized parameter condition, compared with the traditional double-recessed structure 4H-SiC MESFET (DR 4H-SiC MESFET), the direct current (DC) characteristics of the new structure are improved, and the breakdown voltage is increased by 14% to reach 183 V. In radio frequency (RF) characteristics, cut-off frequency is 24.4 GHz, an increase of 11.9 %; maximum operating frequency is 63.9 GHz, an increase of 20.3%; the maximum power added efficiency (PAE) in the L-band and S-band reaches 63.5 %, PAE is 23.7 % higher than the DR structure. At the end of this paper, the new structure is verified for high-energy-efficiency, and the results show that the new structure has great potential in high-frequency applications.