Gate-geometry dependence of electrical characteristics of p-GaN gate HEMTs

Abstract

In this Letter, we experimentally investigate the impact of gate geometry on forward operation of Schottky-gate p-GaN high electron mobility transistors (HEMTs). In particular, we analyze devices with changing gate-metal/p-GaN junction area and p-GaN/AlGaN/GaN heterostructure area in the linear regime. These devices exhibit unique threshold voltage and subthreshold swing scaling dependence with gate geometry that is in contrast with classic field-effect transistors. On the other hand, peak transconductance and ON resistance are found to scale classically. We find that these results arise from the fact that with a Schottky contact to the p-GaN layer, under steady-state conditions, the p-GaN layer voltage is set by current continuity across the gate stack. Furthermore, a detailed scaling study of the gate current reveals that current flow across the p-GaN/AlGaN/GaN heterostructure is not uniform—instead, it preferentially flows through the ungated portion of the p-GaN layer. Our study concludes that in Schottky-type p-GaN gate HEMTs, the respective areas of two junctions constitute an additional design degree of freedom to fine-tune device performance.

Exploring the impact of AlGaN barrier thickness and temperature on normally-on GaN HEMT performance

“…AlGaN/ GaN HEMTs operate in D-mode (depletion mode), which is a normally-on operation mode, as well as E-mode (enhancement mode), which is a normally-off operation mode. In recent years, numerous methods are being investigated, such as recessed gates [3], p-GaN gates [4,5], fluorine implantation [6], and cascade design [7] to achieve normally-off operation of GaN HEMTs. Depending on the application, normally-on or normally-off GaN HEMTs are used.…”

Highly Sensitive Ultraviolet Photodetector Based on an AlGaN/GaN HEMT with Graphene‐On‐p‐GaN Mesa Structure

“…[22,23] The addition of a p-GaN layer to the AlGaN/GaN changes the resulting p-GaN/AlGaN/GaN HEMT (enhancement-mode) from normally-on to normally-off through band bending and suppression of 2-DEG at zero-bias, which leads to low dark current. [31][32][33][34][35] In previously reported enhancementmode p-GaN/AlGaN/GaN photodetectors, the p-GaN acted as the gate by the means of photo induced carriers. However, there are only a very few studies on the utilization of p-GaN/ AlGaN/GaN structure, and most of them focused on phototransistor mode of operation, where the area of the p-GaN optical gate is limited by the transistor geometry.…”

“…However, there are only a very few studies on the utilization of p-GaN/ AlGaN/GaN structure, and most of them focused on phototransistor mode of operation, where the area of the p-GaN optical gate is limited by the transistor geometry. [35][36][37] A widened p-GaN region on the photodetector would broadly and effectively suppress the 2-DEG, which could help in enhancing the photosensitivity through lowering the dark current. Moreover, the detailed operation mechanism and the effect of electrode transmittance on the photodetector performance still need to be explored further.…”