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Creation of Two‐Dimensional Electron Gas and Role of Surface Donors in III‐N Metal‐Oxide‐Semiconductor High‐Electron Mobility Transistors
Author(s) -
Gucmann Filip,
Ťapajna Milan,
Pohorelec Ondrej,
Haščík Štefan,
Hušeková Kristína,
Kuzmík Ján
Publication year - 2018
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201800090
Subject(s) - materials science , high electron mobility transistor , annealing (glass) , oxide , semiconductor , transistor , electron , optoelectronics , threshold voltage , electron mobility , analytical chemistry (journal) , chemistry , voltage , electrical engineering , physics , quantum mechanics , chromatography , metallurgy , composite material , engineering
The role of surface donors at the oxide/semiconductor interface of III‐N metal‐oxide‐semiconductor (MOS) high‐electron mobility transistors (HEMTs), by creating a two‐dimensional electron gas (2DEG) and the device performance, are investigated. Al 2 O 3 /GaN/AlGaN/GaN MOS HEMTs show the surface donor density ( N d,surf ) of 2.2 × 10 13 cm −2 , which is increased up to 3.4 × 10 13 cm −2 after post‐deposition annealing. In the latter, surface donors fully compensate the surface polarization charge and the HEMT threshold voltage decreases substantially with the oxide thickness. On the other hand, an open‐channel drain current is found to be independent of N d,surf , while marginal trapping is completely removed when N d,surf increases with annealing. Consequently, ionized surface donors behave like a fixed charge and are clearly distinguishable from trapping states. Open‐channel 2DEG densities of ≈1.1 × 10 13 cm −2 are extracted from capacitance–voltage measurements. Similarly, recent data on enhancement‐mode HfO 2 /InAlN/AlN/GaN MOS HEMTs are analyzed where N d,surf is reduced down to 1 × 10 13 cm −2 while 2DEG densities reach ≈2.7 × 10 13 cm −2 . It is suggested that under the open‐channel condition, 2DEG is supplied also by an injecting source contact if N d,surf is lower than the QW polarization charge. Our charge quantifications are supported by calculating energy‐band diagrams.