Normally-off GaN HEMTs with InGaN p-gate cap layer formed by polarization doping

Abstract

Narrow gate margin has been the critical limiting factor for the p-gate normally-off GaN HEMTs, imposing significant challenges in both gate-drive design and gate reliability. In this work, by developing dopant-free p-type polarization doping technique in composition-graded InGaN layer, high-quality Schottky contact between the gate metal and cap layer was demonstrated, achieving excellent gate current blocking performance (10-6 mA/mm) after the turning-on of the gate heterojunction structure. Resultantly, normally-off GaN HEMTs with enhanced gate breakdown voltage up to 15.2 V was realized, being especially beneficial for the simplification of gate drive design and the safe operation of gate terminal.

Normally-OFF AlGaN/GaN-based HEMTs with decreasingly graded AlGaN cap layer

“…Facilitated by the graded AlGaN configurations, these polarization charges would be spread out in three-dimensional way, whose charge profiles can be determined by ρ(z) = −∇P tot (z), where z stands for the growth direction. To counterbalance the 3D fixed polarization charges, the mobile 3DHGs are generated in the GACL, forming a p-type conducting cap layer to realize E-mode operation of GaN HEMTs [1,26].…”

“…However, the further increase of V TH for such devices is limited by the relatively low hole concentration in p-GaN cap layer due to the high thermal activation energy of the acceptor impurity Mg in GaN at room temperature [25]. Besides, the large amount of the interstitial Mg impurities could introduce the non-negligible degradation of the Schottky gate contact [26], featuring a large gate leakage current (J G ) [27][28][29][30]. Therefore, it is worth investigating the alternative p-type cap layers to obtain increased V TH , large V GS swing, and suppressed J G .…”

“…For example, Xu et al recently demonstrated a p-type InGaN structure with increasingly graded Indium composition along [0001] direction without any intentional doping. By utilizing such graded InGaN as the p-type cap layer, they successfully realized an E-mode HEMT with a V TH of 1.3 V and V GS swing up to 15 V [26]. In addition, researchers have experimentally confirmed that a decreasingly graded Al composition along [0001] direction in AlGaN alloys can realize a highly conductive p-type layer [33][34][35].…”

The effect of SiN x film for H plasma implantation in p-GaN/AlGaN/GaN high electron mobility transistors

“…To simplify the circuits and improve circuit security, there is often a heavy demand for normallyoff HEMTs. [5][6][7][8] In recent years, p-GaN gate HEMTs have received extensive attention and have been widely used in commerce. [9][10][11][12] The p-GaN gate HEMT is a normally-off device that uses the p-GaN under the gate to form a p-n junction with the 2-DEG in the channel, thus forming a depletion region under the gate and blocking the 2-DEG in the channel.…”