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Title: Ohmic contacts to Al-rich AlGaN heterostructures

Abstract

Due to the ultra-wide bandgap of Al-rich AlGaN, up to 5.8 eV for the structures in this study, obtaining low resistance ohmic contacts is inherently difficult to achieve. A comparative study of three different fabrication schemes is presented for obtaining ohmic contacts to an Al-rich AlGaN channel. Schottky-like behavior was observed for several different planar metallization stacks (and anneal temperatures), in addition to a dry-etch recess metallization contact scheme on Al 0.85Ga 0.15N/Al 0.66Ga 0.34N. However, a dry etch recess followed by n +-GaN regrowth fabrication process is reported as a means to obtain lower contact resistivity ohmic contacts on a Al 0.85Ga 0.15N/Al 0.66Ga 0.34N heterostructure. In conclusion, specific contact resistivity of 5×10 -3 Ω cm 2 was achieved after annealing Ti/Al/Ni/Au metallization.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1398780
Alternate Identifier(s):
OSTI ID: 1374948
Report Number(s):
SAND-2017-9872J
Journal ID: ISSN 1862-6300; 656978
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physica Status Solidi. A, Applications and Materials Science
Additional Journal Information:
Journal Volume: 214; Journal Issue: 8; Journal ID: ISSN 1862-6300
Publisher:
Wiley
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AlGaN; AlN; band gap; heterostructures; ohmic contacts

Citation Formats

Douglas, E. A., Reza, S., Sanchez, C., Koleske, D., Allerman, A., Klein, B., Armstrong, A. M., Kaplar, R. J., and Baca, A. G. Ohmic contacts to Al-rich AlGaN heterostructures. United States: N. p., 2017. Web. doi:10.1002/pssa.201600842.
Douglas, E. A., Reza, S., Sanchez, C., Koleske, D., Allerman, A., Klein, B., Armstrong, A. M., Kaplar, R. J., & Baca, A. G. Ohmic contacts to Al-rich AlGaN heterostructures. United States. doi:10.1002/pssa.201600842.
Douglas, E. A., Reza, S., Sanchez, C., Koleske, D., Allerman, A., Klein, B., Armstrong, A. M., Kaplar, R. J., and Baca, A. G. Tue . "Ohmic contacts to Al-rich AlGaN heterostructures". United States. doi:10.1002/pssa.201600842.
@article{osti_1398780,
title = {Ohmic contacts to Al-rich AlGaN heterostructures},
author = {Douglas, E. A. and Reza, S. and Sanchez, C. and Koleske, D. and Allerman, A. and Klein, B. and Armstrong, A. M. and Kaplar, R. J. and Baca, A. G.},
abstractNote = {Due to the ultra-wide bandgap of Al-rich AlGaN, up to 5.8 eV for the structures in this study, obtaining low resistance ohmic contacts is inherently difficult to achieve. A comparative study of three different fabrication schemes is presented for obtaining ohmic contacts to an Al-rich AlGaN channel. Schottky-like behavior was observed for several different planar metallization stacks (and anneal temperatures), in addition to a dry-etch recess metallization contact scheme on Al0.85Ga0.15N/Al0.66Ga0.34N. However, a dry etch recess followed by n+-GaN regrowth fabrication process is reported as a means to obtain lower contact resistivity ohmic contacts on a Al0.85Ga0.15N/Al0.66Ga0.34N heterostructure. In conclusion, specific contact resistivity of 5×10-3 Ω cm2 was achieved after annealing Ti/Al/Ni/Au metallization.},
doi = {10.1002/pssa.201600842},
journal = {Physica Status Solidi. A, Applications and Materials Science},
number = 8,
volume = 214,
place = {United States},
year = {Tue Jun 06 00:00:00 EDT 2017},
month = {Tue Jun 06 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on June 6, 2018
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Cited by: 5works
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  • Cited by 5
  • The physical mechanism of low-thermal-budget Au-free ohmic contacts to AlGaN/GaN heterostructures is systematically investigated with current-voltage, high-resolution transmission electron microscopy, and temperature-dependent contact resistivity characterizations. With a low annealing temperature of 600 °C, pre-ohmic recess etching of the AlGaN barrier down to several nanometers is demonstrated to be an effective method to reduce the contact resistance between Ti/Al/Ti/W ohmic metals and AlGaN/GaN heterostructures. However, further over recess of the AlGaN barrier leads to only sidewall contact to 2D electron gas channel and thus degraded contact performance. It is verified by temperature-dependent contact resistivity measurements that field emission (tunneling) dominates the currentmore » transport mechanism in Au-free ohmic contacts with AlGaN barrier partially and over recessed, while both field emission and thermionic emission contribute to traditional Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures that annealed at high temperature (850 °C)« less
  • This letter reports on the temperature behavior of the structural and electrical properties of Ti/Al/Ni/Au contacts to AlGaN/GaN heterostructures. While Ohmic contacts formed at 750 °C showed a decreasing temperature behavior of the specific contact resistance ρ{sub C}, which was explained by a thermionic field emission mechanism, an increasing trend is observed in the contacts formed at 850 °C. In this case, ρ{sub C} exhibits a “metal-like” behavior, i.e., describable by a T{sup 1.8} dependence. The microstructural analysis of the interfacial region allowed to explain the results with the formation of metallic intrusions contacting directly the two dimensional electron gas.
  • The electrical behaviour of graphene (Gr) contacts to Al{sub x}Ga{sub 1−x}N/GaN heterostructures has been investigated, focusing, in particular, on the impact of the AlGaN microstructure on the current transport at Gr/AlGaN interface. Two Al{sub 0.25}Ga{sub 0.75}N/GaN heterostructures with very different quality in terms of surface roughness and defectivity, as evaluated by atomic force microscopy (AFM) and transmission electron microscopy, were compared in this study, i.e., a uniform and defect-free sample and a sample with a high density of typical V-defects, which locally cause a reduction of the AlGaN thickness. Nanoscale resolution current voltage (I-V) measurements by an Au coated conductivemore » AFM tip were carried out at several positions both on the bare and Gr-coated AlGaN surfaces. Rectifying contacts were found onto both bare AlGaN surfaces, but with a more inhomogeneous and lower Schottky barrier height (Φ{sub B} ≈ 0.6 eV) for AlGaN with V-defects, with respect to the case of the uniform AlGaN (Φ{sub B} ≈ 0.9 eV). Instead, very different electrical behaviours were observed in the presence of the Gr interlayer between the Au tip and AlGaN, i.e., a Schottky contact with reduced barrier height (Φ{sub B} ≈ 0.4 eV) for the uniform AlGaN and an Ohmic contact for the AlGaN with V-defects. Interestingly, excellent lateral uniformity of the local I-V characteristics was found in both cases and can be ascribed to an averaging effect of the Gr electrode over the AlGaN interfacial inhomogeneities. Due to the locally reduced AlGaN layer thickness, V defect act as preferential current paths from Gr to the 2DEG and can account for the peculiar Ohmic behaviour of Gr contacts on defective AlGaN.« less
  • No abstract prepared.