Si implanted ohmic contacts with modulated pulse activation annealing for down-scaled RF GaN HEMTs

A. Bassal, A. Koyucuoglu, A. Thies, I. Ostermany, P. Pallabi, S. Chevtchenko, and O. Hilt

Published in:

J Appl Phys , Frontiers in Nitride Semiconductors Research, vol. 140, no. 3, pp. 034501, doi:10.1063/5.0331948 (2026).

Abstract:

A modulated pulse annealing method combined with an Al₂O₃/SiN_x annealing cap is utilized for activating implanted Si in n+ ohmic contacts for AlGaN/GaN HEMTs. The objective is to prevent GaN decomposition during annealing and to reduce the alloying temperature of ohmic contacts. This enables the alloying of SiN_x-encapsulated contacts for obtaining smooth ohmic contact edges, which is important for downscaled K_a/K-band HEMTs with a short gate–source distance. Al₂O₃ functions as a diffusion barrier against nitrogen, and SiN_x protects the epitaxial layer stack during cap etching and prevents GaN decomposition due to the loss of N. Furthermore, the Al₂O₃/SiN_x cap acts as a retardation layer for Si implantation to achieve a maximum Si concentration in the GaN channel under the AlGaN barrier. Before activation annealing, H is outgassed from the amorphous Al₂O₃ at 500 °C, which is then crystallized at 900 °C for enhancing its strength. Then it follows the modulated pulsed activation annealing with five pulses peaking at 1250 °C, four pulses at 1300 °C, and one at 1325 °C. The Al₂O₃/SiN_x cap is then removed with dry and wet etching to leave a clean surface, before the deposition of a Ti-based ohmic contact metal. At an implantation dose of 3.5 × 1015 cm^-2, 27% activation is achieved without any GaN decomposition, providing a contact resistance of 0.32 Ω mm after contact alloying only at 650 °C for 5 min.

© 2026 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).
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