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Simple ohmic contact formation in HEMT structures: application to AlGaN/GaN
Author(s): Clarissa D. Vazquez-Colon; David C. Look; Eric Heller; John S. Cetnar; Arturo A. Ayon
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Paper Abstract

Low-resistance ohmic contacts on AlGaN/GaN HEMT devices presently require annealing at temperatures up to 850°C, which can adversely affect material properties. Here we investigate contacts with the metal directly contacting the 2DEG in the GaN, about 20 nm below the top surface. For convenience, we employed a 10-mm × 10-mm sample composed of 3-nm-GaN/16-nm-Al0.27Ga0.73N/1-nm-AlN/1.8-μm-GaN (Fe-doped). Four, 2-mm-long, 2-μm deep lines were scribed near the corners of the sample and filled with indium metal from a soldering iron. Hall measurements were then performed from 10 to 320 K at a current of 1 mA and with a magnetic field strength of 10 kG. At 10K (300K) the mobility was 1.96 × 104 (1.88 × 103) cm2·V-1·s-1; the sheet concentration, 9.39 × 1012 (9.35 × 1012) cm-2, and the sheet resistance, 33.9 (353) Ω/sq = rs. The contact resistance Rc was calculated from the average total resistance Rtot across each pair of contacts: Rtot = 2Rc + rs. At 10 K (300 K), Rc ≈ 1 (2) kΩ. Also, Rc has a much smaller temperature dependence than rs, implying tunneling, rather than thermionic current. From a Schrödinger-Poisson calculation, the peak volume carrier concentration in the 2DEG is n ≈ 3.7 × 1019 cm-3. The tunneling probability is P = exp[e(V – Vbi)/ε00] and for ε = 9.9εvac and m* = 0.22m0, ε00 = 0.077 eV = 894 K; thus, ε00 < kT, further suggesting the dominance of tunneling current. This technique is immediately applicable to any HEMT-type structure, including AlScN/GaN.

Paper Details

Date Published: 1 March 2019
PDF: 7 pages
Proc. SPIE 10918, Gallium Nitride Materials and Devices XIV, 1091819 (1 March 2019); doi: 10.1117/12.2510348
Show Author Affiliations
Clarissa D. Vazquez-Colon, The Univ. of Texas at San Antonio (United States)
Air Force Research Lab. (United States)
KBRwyle (United States)
David C. Look, Air Force Research Lab. (United States)
Wright State Univ. (United States)
Eric Heller, Air Force Research Lab. (United States)
John S. Cetnar, Air Force Research Lab. (United States)
Arturo A. Ayon, The Univ. of Texas at San Antonio (United States)


Published in SPIE Proceedings Vol. 10918:
Gallium Nitride Materials and Devices XIV
Hiroshi Fujioka; Hadis Morkoç; Ulrich T. Schwarz, Editor(s)

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