Simple ohmic contact formation in HEMT structures: application to AlGaN/GaN

Clarissa D. Vazquez-Colon; David C. Look; Eric Heller; John S. Cetnar; Arturo A. Ayon

doi:10.1117/12.2510348

1 March 2019 Simple ohmic contact formation in HEMT structures: application to AlGaN/GaN

Clarissa D. Vazquez-Colon, David C. Look, Eric Heller, John S. Cetnar, Arturo A. Ayon

Proceedings Volume 10918, Gallium Nitride Materials and Devices XIV; 1091819 (2019) https://doi.org/10.1117/12.2510348
Event: SPIE OPTO, 2019, San Francisco, California, United States

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-Al_0.27Ga_0.73N/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 = r_s. The contact resistance R_c was calculated from the average total resistance R_tot across each pair of contacts: R_tot = 2R_c + r_s. At 10 K (300 K), R_c ≈ 1 (2) kΩ. Also, R_c has a much smaller temperature dependence than r_s, 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 – V_bi)/ε₀₀] and for ε = 9.9ε_vac 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.

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Citation Download Citation

Clarissa D. Vazquez-Colon, David C. Look, Eric Heller, John S. Cetnar, and Arturo A. Ayon "Simple ohmic contact formation in HEMT structures: application to AlGaN/GaN ", Proc. SPIE 10918, Gallium Nitride Materials and Devices XIV, 1091819 (1 March 2019); https://doi.org/10.1117/12.2510348

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