Vertical 3D gallium nitride field-effect transistors based on fin structures with inverted p-doped channel

authored by: Klaas Strempel, Friedhard Römer, Feng Yu, Matteo Meneghini, Andrey Bakin, Hergo Heinrich Wehmann, Bernd Witzigmann, Andreas Waag
Abstract: This paper demonstrates the first vertical field-effect transistor based on gallium nitride (GaN) fin structures with an inverted p-doped channel layer. A top-down hybrid etching approach combining inductively coupled plasma reactive ion etching and KOH-based wet etching was applied to fabricate regular fields of GaN fins with smooth a-plane sidewalls. The obtained morphologies are explained using a cavity step-flow model. A 3D processing scheme has been developed and evaluated via focussed ion beam cross-sections. The top-down approach allows the introduction of arbitrary doping profiles along the channel without regrowth, enabling the modulation of the channel properties and thus increasing the flexibility of the device concept. Here, a vertical npn-doping profile was used to achieve normally-off operation with an increased threshold voltage as high as 2.65 V. The p-doped region and the 3D gate wrapped around the sidewalls create a very narrow vertical electron channel close to the interface between dielectric and semiconductor, resulting in good electrostatic gate control, low leakage currents through the inner fin core and high sensitivity to the interface between GaN and gate oxide. Hydrodynamic transport simulations were carried out and show good agreement with the performed current-voltage and capacitance-voltage measurements. The simulation indicates a reduced channel mobility which we attribute to interface scattering being particularly relevant in narrow channels. We also demonstrate the existence of oxide and interface traps with an estimated sheet density of 3.2 × 1012 cm-2 related to the Al2O3 gate dielectric causing an increased subthreshold swing. Thus, improving the interface quality is essential to reach the full potential of the presented vertical 3D transistor concept.
External Organisation(s): Technische Universität Braunschweig
University of Kassel
University of Padova
Type: Article
Journal: Semiconductor Science and Technology
Volume: 36
ISSN: 0268-1242
Publication date: 01.2021
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Electronic version(s): https://doi.org/10.1088/1361-6641/abc5ff (Access: Open)

BibTeX

@article{f2a86e63b51340d1afbc05793724b55c,
title = "Vertical 3D gallium nitride field-effect transistors based on fin structures with inverted p-doped channel",
abstract = "This paper demonstrates the first vertical field-effect transistor based on gallium nitride (GaN) fin structures with an inverted p-doped channel layer. A top-down hybrid etching approach combining inductively coupled plasma reactive ion etching and KOH-based wet etching was applied to fabricate regular fields of GaN fins with smooth a-plane sidewalls. The obtained morphologies are explained using a cavity step-flow model. A 3D processing scheme has been developed and evaluated via focussed ion beam cross-sections. The top-down approach allows the introduction of arbitrary doping profiles along the channel without regrowth, enabling the modulation of the channel properties and thus increasing the flexibility of the device concept. Here, a vertical npn-doping profile was used to achieve normally-off operation with an increased threshold voltage as high as 2.65 V. The p-doped region and the 3D gate wrapped around the sidewalls create a very narrow vertical electron channel close to the interface between dielectric and semiconductor, resulting in good electrostatic gate control, low leakage currents through the inner fin core and high sensitivity to the interface between GaN and gate oxide. Hydrodynamic transport simulations were carried out and show good agreement with the performed current-voltage and capacitance-voltage measurements. The simulation indicates a reduced channel mobility which we attribute to interface scattering being particularly relevant in narrow channels. We also demonstrate the existence of oxide and interface traps with an estimated sheet density of 3.2 × 1012 cm-2 related to the Al2O3 gate dielectric causing an increased subthreshold swing. Thus, improving the interface quality is essential to reach the full potential of the presented vertical 3D transistor concept.",
keywords = "field-effect transistor, gallium nitride, nanostructures, vertical electronics",
author = "Klaas Strempel and Friedhard R{\"o}mer and Feng Yu and Matteo Meneghini and Andrey Bakin and Wehmann, {Hergo Heinrich} and Bernd Witzigmann and Andreas Waag",
note = "Acknowledgments This work was funded by the Deutsche Forschungsgesellschaft (DFG, German Research Formation) within the project {\textquoteleft}3D Concepts for Gallium Nitride Electroncis{\textquoteright}— 284575374 and under Germany{\textquoteright}s Excellence Strategy—EXC- 2123 Quantum Frontiers—390837967. The authors thank I. Manglano Clavero and C. Margenfeld for wafer growth in the Epitaxy Competence Center (ec2), a joint venture by the Institute of Semiconductor Technology and OSRAM Opto Semiconductors. We gratefully acknowledge the technical assistance of Juliane Breitfelder, Diana Herz and Angelika Schmidt.",
year = "2021",
month = jan,
doi = "10.1088/1361-6641/abc5ff",
language = "English",
volume = "36",
journal = "Semiconductor Science and Technology",
issn = "0268-1242",
publisher = "IOP Publishing Ltd.",
number = "1",
}