In this Letter, we investigate the threshold voltage (VTH) instability of Schottky p-GaN gate high electron mobility transistors (SP-HEMTs) under high-frequency operation by a resistive-load hard switching method. The abnormal VTH instability is observed, which is different between fully and partially depleted SP-HEMTs (FD- and PD-HEMTs). Notably, for FD-HEMT, VTH shifts positively with effective stress time. However, the VTH instability in PD-HEMT is more complex. At low VGS (e.g., 3 V) and high VGS (e.g., 6 V), VTH shifts positively with stress time consistently. Nevertheless, at intermediate VGS levels (e.g., 4 and 5 V), VTH initially shifts positively and then negatively, displaying a non-monotonous variation. Furthermore, the frequency dependence of VTH is contingent upon VGS. At low VGS, VTH exhibits a negative shift with the increase in frequency. This trend inverses when VGS exceeds 4 V. And it should be noted that the extracted VTH under high-frequency operation is lower than their quasi-static values for both transistor types. This work depicts the physical process and mechanism of the abnormal VTH instability; different from the quasi-static case, hole accumulation effects will be enhanced due to the high dV/dt, which results in a lower VTH. The distinct VTH behaviors of FD- and PD-HEMTs are closely related to the trapping effects, as well as hole accumulation and insufficiency, within the two different p-GaN gate layers.

中文翻译：

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高频工作下肖特基 p-GaN HEMT 异常 VTH 不稳定性的物理洞察

在这封信中，我们通过电阻负载硬开关方法研究了肖特基 p-GaN 栅极高电子迁移率晶体管 (SP-HEMT) 在高频操作下的阈值电压 (VTH) 不稳定性。观察到异常的 VTH 不稳定性，这在完全耗尽和部分耗尽的 SP-HEMT（FD- 和 PD-HEMT）之间是不同的。值得注意的是，对于 FD-HEMT，VTH 随有效应力时间呈正向变化。然而，PD-HEMT 中的 VTH 不稳定性更为复杂。在低VGS（例如，3V）和高VGS（例如，6V）下，VTH 随应力时间一致地正向变化。然而，在中间VGS 水平（例如4 和5V），VTH 最初正向移动，然后负向移动，显示出非单调变化。此外，VTH 的频率依赖性取决于 VGS。在低 VGS 下，VTH 随着频率的增加而呈现负移。当 VGS 超过 4V 时，这种趋势会反转。值得注意的是，高频操作下提取的 VTH 低于两种晶体管类型的准静态值。这项工作描绘了异常VTH不稳定的物理过程和机制；与准静态情况不同，由于dV/dt较高，空穴积累效应会增强，从而导致较低的VTH。 FD-和PD-HEMT 的不同VTH 行为与两个不同p-GaN 栅极层内的俘获效应以及空穴积累和不足密切相关。