Design principle for a p-type oxide gate layer on AlGaN/GaN toward normally-off HEMTs: Li-doped NiO as a model. Issue 3 (17th December 2019)

• Record Type: Journal Article
• Authors: Li, Guanjie; Li, Xiaomin; Zhao, Junliang; Yan, Fawang; Zhu, Qiuxiang; Gao, Xiangdong
• Is Part Of: Journal of materials chemistry. Volume 8:Issue 3(2019)
• Page Start: 1125
• Page End: 1134
• Publication Date: 2019-12-17
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9tc04467a
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : The band alignment matching between p-type oxide and AlGaN/GaN is revealed to be key factor for p-type oxide gated normally-off HEMTs. 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%, Ni0.75 Li0.25 O 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 × 10 19 cm −3 . Nevertheless, the Ni0.75 Li0.25 O/AlGaN/GaN/Si heterostructure still suffers from a low threshold voltage of merely −2.12 V. By resolving the band alignment at the Ni0.75 Li0.25 O/AlGaN interface and the depletion mechanism for p-type Ni0.75 Li0.25 O 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.