Performance Enhancement of Normally-Off Plasma-Assisted Atomic Layer Deposited Al₂O₃/GaN Metal–Oxide–Semiconductor Field-Effect Transistor with Postdeposition Annealing

Abstract

A normally-off GaN-based metal–oxide–semiconductor field effect transistor (MOSFET) was fabricated using the Al0.3Ga0.7N/GaN heterostructure with a two-dimensional electron gas (2DEG) density of ∼1×1014 cm-2 grown on a silicon substrate. The AlGaN layer in the gate region was fully recessed and the whole surface of the device was covered with a high-quality plasma-assisted atomic-layer-deposited (PAALD) Al2O3 layer, which plays the role of not only a gate insulator in the recessed gate region, but also a surface passivation layer in the ungated region between the source and the drain. The fabricated Al2O3/GaN MOSFET exhibited excellent device properties, such as a threshold voltage of 1.1 V extrapolated in the linear region at a drain voltage of 0.1 V, maximum drain current of 353 mA/mm, field-effect mobility of 225 cm2·V-1·s-1, and on-resistance of 9.7 Ω·mm, which are among the best values ever reported for GaN MOSFETs fabricated on silicon substrates.

Normally off AlGaN/GaN HEMT on Si substrate with selectively dry-etched recessed gate and polarization-charge-compensation δ-doped GaN cap layer

“…It is difficult to fulfill these two conflicting demands in a lateral planar structure. Therefore, several technologies forming a structural step between the source and the drain electrode, such as a recessed gate structure [9][10][11][12][13][14][15][16] and a p-AlGaN or -GaN gate 17,18) structure, have been proposed to date for realizing normally off characteristics in GaN-based HEMTs.…”