In this paper, DC, transient, and RF performances among AlGaN/GaN HEMTs with a no field plate structure (basic), a conventional gate field plate structure (GFP), and a double floating field plate structure (2FFP) were studied by utilizing SILVACO ATLAS 2D device technology computer-aided design (TCAD). The peak electric fields under the gate in drain-side can be alleviated effectively in 2FFP devices, compared with basic and GFP devices, which promotes the breakdown voltage (BV) and suppresses the current collapse phenomenon. As a result, the ON-resistance increase caused by the current collapse phenomena is dramatically suppressed in 2FFP ~19.9% compared with GFP ~49.8% when a 1 ms duration pre-stress was applied with V_ds = 300 V in the OFF-state. Because of the discontinuous FP structure, more electric field peaks appear at the edge of the FFP stacks, which leads to a higher BV of ~454.4 V compared to the GFP ~394.3 V and the basic devices ~57.6 V. Moreover, the 2FFP structure performs lower a parasitic capacitance of C_gs = 1.03 pF and C_gd = 0.13 pF than those of the GFP structure (i.e., C_gs = 1.89 pF and C_gd = 0.18 pF). Lower parasitic capacitances lead to a much higher cut-off frequency (f_t) of 46 GHz and a maximum oscillation frequency (f_max) of 130 GHz than those of the GFP structure (i.e., f_t = 27 GHz and f_max = 93 GHz). These results illustrate the superiority of the 2FFP structure for RF GaN HEMT and open up enormous opportunities for integrated RF GaN devices.

Achieving low conduction loss and good channel mobility is crucial for SiC MOSFETs. However, basic planar SiC MOSFETs provide challenges due to their high density of interface traps and significant gate-to-drain capacitance. In order to enhance the reverse recovery property of the device, a Schottky barrier diode (SBD) was added to the source contact area, the top of the current spreading region, of a trench-etched double-diffused SiC MOS (TED MOS). Two types of SBD structures were optimized to improve the electrical properties using 3D simulation software, “TCAD Silvaco”. During reverse recovery simulation, the carriers of the device were withdrawn from the SBD, indicating that the new design was effective. It also showed that the recovery properties of the new design depended on temperature, carrier lifetime, and the work functions of metals. All the new designs were evaluated in various circumstances to determine the trend. Ultimately, in high-speed switching circuits, the SiC TED MOS with SBD structure efficiently boosted switching speed, while reducing switching loss.

In the traditional SJ MOSFET structure, n/p pillars with the same doping concentrations in the drift region are introduced to decrease the on-resistance. However, SJ MOSFET will turn on the parasitic diodes due to fast reverse recovery, further inducing severe oscillation in the reverse recovery of the device and the corresponding adverse effect on the circuit. In this study, a fast recovery vertical superjunction (SJ) MOSFET with n-Si and p-3C-SiC pillars was studied. Unlike other structures, such as the 4H-SiC superjunction UMOSFET with a heterojunction diode or the ultra-low recovery charge cell-distributed Schottky contacts SJ-MOSFET with integrated isolated NMOS, we introduce a Schottky barrier diode (SBD) on the source contact at the top of the n-Si pillar in the SJ-MOSFET to improve the device reverse recovery. The simulation software TCAD Silvaco was utilized to simulate the device properties. Compared with the conventional Si SJ, the proposed Si/SiC SJ with the Schottky barrier diode (SBD) connected demonstrated a lower reverse recovery charge, which was reduced by 90.5%, respectively. The waveform of the reverse recovery current demonstrates that the electrons in the device are withdrawn from SBD during reverse recovery, preventing the opening of the parasitic diode in the SJ MOSFET. Finally, another structure is illustrated to decrease the gate capacitance by introducing a thin p-base layer between the gate metal and N-Si pillar so that it can improve the switching characteristics of devices. The open-loss and off-loss of the improved device were reduced by 33% and 42.3%, respectively.