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Issue 3, 2020
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Design principle for a p-type oxide gate layer on AlGaN/GaN toward normally-off HEMTs: Li-doped NiO as a model

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Abstract

Integration of the p-type oxide gate layer on AlGaN/GaN is a promising approach to explore normally-off high electron mobility transistors (HEMTs). However, the critical reason for the ultralow threshold voltage in intrinsic p-type oxide gated HEMTs remains elusive. Herein, Li-doped NiO thin films with various doping contents were grown on AlGaN/GaN/Si substrates by pulsed laser deposition (PLD) to identify the most important physical properties and design principle of p-type oxide for normally-off HEMTs. With the increasing Li doping content up to 25%, Ni0.75Li0.25O on AlGaN/GaN exhibits excellent epitaxial growth quality with good interfacial state, a wide band gap of 3.65 eV and an ultrahigh hole concentration of 6.81 × 1019 cm−3. Nevertheless, the Ni0.75Li0.25O/AlGaN/GaN/Si heterostructure still suffers from a low threshold voltage of merely −2.12 V. By resolving the band alignment at the Ni0.75Li0.25O/AlGaN interface and the depletion mechanism for p-type Ni0.75Li0.25O on 2DEG, the band alignment matching is ascribed to be the most critical issue for intrinsic p-type oxide gated normally-off HEMTs with a low threshold voltage, that is, a relatively small energy level difference value between the conduction band of GaN and the valence band of intrinsic p-type oxide. Based on the results, the design principle of the p-type oxide gate layer on AlGaN/GaN for normally-off HEMTs is proposed, and p-type oxides doped from intrinsic n-type oxides are suspected to be competitive candidates.

Graphical abstract: Design principle for a p-type oxide gate layer on AlGaN/GaN toward normally-off HEMTs: Li-doped NiO as a model

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Supplementary files

Article information


Submitted
12 Aug 2019
Accepted
03 Dec 2019
First published
06 Dec 2019

J. Mater. Chem. C, 2020,8, 1125-1134
Article type
Paper

Design principle for a p-type oxide gate layer on AlGaN/GaN toward normally-off HEMTs: Li-doped NiO as a model

G. Li, X. Li, J. Zhao, F. Yan, Q. Zhu and X. Gao, J. Mater. Chem. C, 2020, 8, 1125
DOI: 10.1039/C9TC04467A

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