| Summary: | 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 (<i>V<sub>knee</sub></i>), saturation current density (<i>I<sub>d-sat</sub></i>), and cut-off frequency (<i>f<sub>t</sub></i>) of its high electron mobility transistor (HEMT) are simulated and analyzed. A novel optimization factor <i>OPTIM</i> is proposed by considering the various performance parameters of the device to reduce the <i>V<sub>knee</sub></i> and improve the <i>I<sub>d-sat</sub></i> on the premise of ensuring the <i>f<sub>t</sub></i>. 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<sub>g</sub> 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>I<sub>d-sat</sub></i> of 750 mA/mm and a low <i>V<sub>knee</sub></i> of 2.0 V and presents <i>f<sub>t</sub></i> and maximum frequency (<i>f<sub>max</sub></i>) 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 <i>OPTIM</i> can provide an effective design method for follow-up high-frequency and low-voltage applications of GaN devices.
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