(Invited) Threshold Voltage Modulation By Interface Charge Engineering for High Performance Enhancement-Mode Al2O3/GaN Power Mosfets

Abstract

III-Nitride metal-oxide-semiconductor field effect transistors (MOSFETs) have great potential for next generation energy-efficient power switching. Due to the fail-safe consideration, the enhancement-mode (E-mode) operation is highly desirable for GaN MOSFETs in power electronics. Furthermore, in high frequency switching applications, devices with high V TH (e.g. V TH>6 V) and large gate swing (e.g. >10 V) are required to prevent them from faulty turn-on due to the gate driver failure or electromagnetic interference. Many approaches have been demonstrated in pushing the V TH more positive [1], [2]. However, achieving high V TH and good performance simultaneously remains a major challenge due to positive interface fixed charges [3], [4]. In this paper, the presence of positive interface fixed charges (Q it~1.44×1013 cm-2) at the ALD-Al2O3/GaN interface was found in the fully recessed Al2O3/GaN MOSFETs. The origin of the interface charges is proposed to be the Ga-O bond and metal Ga dangling bond (DB) at the Al2O3/GaN interface generated in the gate recessing process and Al2O3 deposition, respectively. An efficient approach to engineer the interface positive fixed charges was demonstrated by post-dielectric annealing (PDA) in N2, resulting in a reduction of Q it from 1.44×1013 to 3×1012 cm-2. The reduction of Q it leads to a significant positive shift in V TH and an increase of electron mobility that enabling the E-mode operation of Al2O3/GaN MOSFETs with a uniquely high V TH of +7.6 V and drive current as high as 355 mA/mm. The interface charge engineering method demonstrated in this work is promising to fabricate E-mode GaN devices with uniquely higher V TH and low on-resistance.