A1 Refereed original research article in a scientific journal
Surface Properties of p‐GaN and Formation of Nickel Metal Contacts
Authors: Miettinen, Mikko; Nuutila, Vesa; Jahanshah Rad, Zahra; Ebrahimzadeh, Masoud; Ruokonen, Anni; Punkkinen, Risto; Lehtio, Juha-Pekka; Punkkinen, Marko; Laukkanen, Pekka; Kokko, Kalevi; Suihkonen, Sami; Savin, Hele; Wang, Weimin
Publisher: Wiley
Publishing place: HOBOKEN
Publication year: 2025
Journal: Advanced Materials Interfaces
Journal name in source: Advanced Materials Interfaces
Journal acronym: ADV MATER INTERFACES
Article number: 2500163
Volume: 12
Issue: 13
Number of pages: 9
ISSN: 2196-7350
eISSN: 2196-7350
DOI: https://doi.org/10.1002/admi.202500163
Web address : https://doi.org/10.1002/admi.202500163
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/499521532
Nickel (Ni) is the key component in ohmic contacts for Mg-doped p-GaN, but the detailed formation mechanisms of the ohmic contact have not yet been understood. In this work, the effect of potassium hydroxide (KOH)-based chemical treatment on the surface of p-GaN is investigated using X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). Ni metal contacts on the chemically treated p-GaN surface are studied using transfer length method (TLM) and synchrotron radiation photoelectron spectroscopy (SR-XPS). The chemical treatment of p-GaN improves the brightness of the (1x1) hexagonal diffraction pattern in LEED and keeps the 2D terrace structure in STM visible. Concomitantly, XPS shows that the amount of O, C, and Mg-O bonds at the surface were reduced. Ni/p-GaN provided an ohmic contact after annealing in ultra-high vacuum (UHV) at 500 degrees C. Simultaneously, SR-XPS shows the diffusion of Ga to Ni and the formation of a previously unreported Ga 3d component, which has a surprisingly narrow line shape, indicating that it originates from a crystalline interface phase. Diffusion of Ga is discussed to cause Ga vacancies and acceptor levels in the bandgap increasing carrier tunneling, thus enabling ohmic contact.
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Funding information in the publication:
The authors thank the MAX IV and its staff for the possibility to conduct experiments at the FinEstBeams beam line. Financial support from Research Council of Finland and University of Turku Graduate School is acknowledged.
