Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

Journal Article · Mon Jun 16 00:00:00 EDT 2014 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4884416· OSTI ID:22300256

Sque, S. J.; Heil, S. B. S. ^[1]; Gravesteijn, D. J. ^[1]; Rietveld, F. J. R. ^[2]; Schmitz, J. ^[3]

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1. NXP Semiconductors Research, High Tech Campus 46, 5656 AE, Eindhoven (Netherlands)
2. NXP Semiconductors, Gerstweg 2, 6534 AE, Nijmegen (Netherlands)
3. MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede (Netherlands)

For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact is thought to come from reactions between the contact metals and the AlGaN/GaN. As a consequence, conventional extraction of the specific contact resistance and transfer length leads to erroneous results. In this Letter, the sheet resistance under gold-free Ti/Al-based Ohmic contacts to AlGaN/GaN heterostructures on Si substrates has been investigated by means of electrical measurements, transmission electron microscopy, and technology computer-aided design simulations. It was found to be significantly lower than that outside of the contact area; temperature-dependent electrical characterization showed that it exhibits semiconductor-like behavior. The increase in conduction is attributed to n-type activity of nitrogen vacancies in the AlGaN. They are thought to form during rapid thermal annealing of the metal stack when Ti extracts nitrogen from the underlying semiconductor. The high n-type doping in the region between the metal and the 2-dimensional electron gas pulls the conduction band towards the Fermi level and enhances horizontal electron transport in the AlGaN. Using this improved understanding of the properties of the material underneath the contact, accurate values of transfer length and specific contact resistance have been extracted.

• OSTI ID: 22300256
• Journal Information: Applied Physics Letters, Vol. 104, Issue 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALUMINIUM
ALUMINIUM COMPOUNDS
ANNEALING
ELECTRIC CONDUCTIVITY
ELECTRIC CONTACTS
ELECTRON GAS
EXTRACTION
FERMI LEVEL
GALLIUM NITRIDES
GOLD
LEAD
SEMICONDUCTOR DEVICES
SEMICONDUCTOR MATERIALS
SIMULATION
SUBSTRATES
TEMPERATURE DEPENDENCE
TITANIUM
TRANSMISSION ELECTRON MICROSCOPY