ED-Tue-P51 - AlScN/GaN (MIS)HEMTs grown by Metal-Organic Chemical Vapor Deposition

4. Electronic devices
Alexander Schmid¹ , Peter D. B. Fischer¹, Franziska C. Beyer², Ali Yassine³, Isabel Streicher⁴, Teresa Duarte⁵, Stefano Leone⁵, Oliver Ambacher³, Johannes Heitmann^1
1 TU Bergakademie Freiberg, Institute of Applied Physics, Freiberg, Germany
² Fraunhofer Institute for Integrated Systems and Device Technology, Freiberg, Germany
³ University of Freiburg, Department of Sustainable Systems Engineering, Freiburg, Germany
⁴ Consiglio Nazionale delle Ricerche - Istituto per la Microelettronica e Microsistemi (CNR-IMM), Catania, Italy
⁵ Fraunhofer Institute for Applied Solid State Physics, Freiburg, Germany

Abstract text
AlScN/GaN heterostructures are a promising material system for high electron mobility transistors (HEMTs). The large polarization charge enables a high sheet carrier density n_s of up to 5∙10¹³ cm^-2 in the two-dimensional electron gas (2DEG) at the AlScN/GaN interface [1]. Compared to Al_0.25Ga_0.75N/GaN heterostructures this is an increase by a factor of five which could lead to a reduced on-state resistance of the devices [2]. However, the high AlN-content, which is typically above 80%, leads to a large contact resistance R_C [3]. Additionally, the growth by molecular beam epitaxy (MBE) [4] limits the scalability due to high cost, low growth rate and small sample size.

This work focuses on the fabrication and electrical characterization of (MIS)HEMTs grown by a metal-organic chemical vapor deposition (MOCVD) [5]. Two different heterostructures were prepared on 4” sapphire substrates. The barrier consists of a 10 nm thick Al_0.89Sc_0.11N layer grown on a thin AlN interlayer. The GaN buffer layer had a thickness of ~2 µm. During growth, sample A was in-situ capped with a 15.5 nm thick SiN layer, while sample B had a 3 nm GaN capping layer. (Ti/Zr)/Al/Ni/Au stacks annealed at 900°C were used as ohmic contacts. A wet chemical treatment was used to micropattern the contact area before metal deposition and hence reduce R_C. Additionally, the SiN cap was removed beneath the gate contact to compare MISHEMT and HEMT devices with the same heterostructure. The HEMT devices showed a saturation current I_d,sat of up to 400 mA/mm for devices with 15 µm channel length. The I_d,on/I_d,off ratio was close to 8 orders of magnitude, indicating the high structural quality of the barrier and low gate leakage current. Two main limitations were found, the still comparable large contact resistance of 1.4 Ωmm and the increase of the sheet resistance R_sh from 283 Ω/sq to 581Ω/sq during device processing. The smallest R_sh degradation was observed with SiN capping, which protects the barrier from decomposition and oxidation during contact anneal.



[1] M. A. Caro et al., J. Phys.: Condens. Matter 27, 245901 (2015)

[2] O. Ambacher et al., J. Appl. Phys. 85, 3222–3233 (1999)

[3] S. Krause et al., IEEE Electron Device Lett. 44 (1), 17-20 (2023)

[4] A. J. Green et al., IEEE Electron Device Lett. 40 (7), 1056-1059 (2019)

[5] I. Streicher et al., Phys. Status Solidi RRL 17(2), 2200387 (2023)