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Surface Properties of p-GaN and Formation of Nickel Metal Contacts

Miettinen, Mikko ; Nuutila, Vesa ; Jahanshah Rad, Zahra ; Ebrahimzadeh, Masoud ; Ruokonen, Anni ; Punkkinen, Risto ; Lehtiö, Juha Pekka ; Punkkinen, Marko ; Laukkanen, Pekka and Kokko, Kalevi , et al. (2025) In Advanced Materials Interfaces 12(13).
Abstract

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,... (More)

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 °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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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Ni, p-GaN, SR-XPS
in
Advanced Materials Interfaces
volume
12
issue
13
article number
2500163
publisher
John Wiley & Sons Inc.
external identifiers
  • scopus:105008011837
ISSN
2196-7350
DOI
10.1002/admi.202500163
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Author(s). Advanced Materials Interfaces published by Wiley-VCH GmbH.
id
3394dbcb-c802-419f-a5bf-945fb3203e75
date added to LUP
2025-12-11 09:49:53
date last changed
2025-12-12 11:40:40
@article{3394dbcb-c802-419f-a5bf-945fb3203e75,
  abstract     = {{<p>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 °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.</p>}},
  author       = {{Miettinen, Mikko and Nuutila, Vesa and Jahanshah Rad, Zahra and Ebrahimzadeh, Masoud and Ruokonen, Anni and Punkkinen, Risto and Lehtiö, Juha Pekka and Punkkinen, Marko and Laukkanen, Pekka and Kokko, Kalevi and Suihkonen, Sami and Savin, Hele and Wang, Weimin}},
  issn         = {{2196-7350}},
  keywords     = {{Ni; p-GaN; SR-XPS}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{13}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{Advanced Materials Interfaces}},
  title        = {{Surface Properties of p-GaN and Formation of Nickel Metal Contacts}},
  url          = {{http://dx.doi.org/10.1002/admi.202500163}},
  doi          = {{10.1002/admi.202500163}},
  volume       = {{12}},
  year         = {{2025}},
}