A Simulation Optimization Factor of Si(111)-Based AlGaN/GaN Epitaxy for High Frequency and Low-Voltage-Control High Electron Mobility Transistor Application

The effects of barrier layer thickness, Al component of barrier layer, and passivation layer thickness of high-resistance Si (111)-based AlGaN/GaN heterojunction epitaxy on the knee-point voltage (V(knee)), saturation current density (I(d-sat)), and cut-off frequency (f(t)) of its high electron mobility transistor (HEMT) are simulated and analyzed. A novel optimization factor OPTIM is proposed by considering the various performance parameters of the device to reduce the V(knee) and improve the I(d-sat) on the premise of ensuring the f(t). Based on this factor, the optimized AlGaN/GaN epitaxial structure was designed with a barrier layer thickness of 20 nm, an Al component in the barrier layer of 25%, and a SiN passivation layer of 6 nm. By simulation, when the gate voltage V(g) is 0 V, the designed device with a gate length of 0.15 μm, gate-source spacing of 0.5 μm, and gate-drain spacing of 1 μm presents a high I(d-sat) of 750 mA/mm and a low V(knee) of 2.0 V and presents f(t) and maximum frequency (f(max)) as high as 110 GHz and 220 GHz, respectively. The designed device was fabricated and tested to verify the simulation results. We demonstrated the optimization factor OPTIM can provide an effective design method for follow-up high-frequency and low-voltage applications of GaN devices.