High-density polarization-induced 2D electron gases in N-polar pseudomorphic undoped GaN/Al0.85Ga0.15N heterostructures on single-crystal AlN substrates

The polarization difference and band offset between Al(Ga)N and GaN induce two-dimensional (2D) free carriers in Al(Ga)N/GaN heterojunctions without any chemical doping. A high-density 2D electron gas (2DEG), analogous to the recently discovered 2D hole gas in a metal-polar structure, is predicted i...

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Bibliographic Details
Published in:Applied physics letters 2022-08, Vol.121 (8)
Main Authors: Zhang, Zexuan, Encomendero, Jimy, Kim, Eungkyun, Singhal, Jashan, Cho, YongJin, Nomoto, Kazuki, Toita, Masato, Xing, Huili Grace, Jena, Debdeep
Format: Article
Language:English
Subjects:
Aluminum gallium nitrides
Aluminum nitride
Applied physics
Cryogenic temperature
Electron density
Electron gas
Gallium nitrides
Heterojunctions
Heterostructures
High electron mobility transistors
Molecular beam epitaxy
Polarization
Room temperature
Semiconductor devices
Single crystals
Substrates
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Summary:The polarization difference and band offset between Al(Ga)N and GaN induce two-dimensional (2D) free carriers in Al(Ga)N/GaN heterojunctions without any chemical doping. A high-density 2D electron gas (2DEG), analogous to the recently discovered 2D hole gas in a metal-polar structure, is predicted in a N-polar pseudomorphic GaN/Al(Ga)N heterostructure on unstrained AlN. We report the observation of such 2DEGs in N-polar undoped pseudomorphic GaN/AlGaN heterostructures on single-crystal AlN substrates by molecular beam epitaxy. With a high electron density of ∼4.3 × 10 13/cm2 that maintains down to cryogenic temperatures and a room temperature electron mobility of ∼450 cm2/V s, a sheet resistance as low as ∼320 Ω / ◻ is achieved in a structure with an 8 nm GaN layer. These results indicate significant potential of AlN platform for future high-power RF electronics based on N-polar III-nitride high electron mobility transistors.
ISSN:0003-6951
1077-3118
DOI:10.1063/5.0107159