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Temperature Behavior of Pt/Au Ohmic Contacts to p-GaN

Published online by Cambridge University Press:  10 February 2011

D. J. King ,
L. Zhang ,
J. C. Ramer ,
S. D. Hersee  and
L. F. Lester
D. J. King
Affiliation:
University of New Mexico, Center for High Technology Materials, Albuquerque, NM
L. Zhang
Affiliation:
University of New Mexico, Center for High Technology Materials, Albuquerque, NM
J. C. Ramer
Affiliation:
University of New Mexico, Center for High Technology Materials, Albuquerque, NM
S. D. Hersee
Affiliation:
University of New Mexico, Center for High Technology Materials, Albuquerque, NM
L. F. Lester
Affiliation:
University of New Mexico, Center for High Technology Materials, Albuquerque, NM
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Abstract

Ohmic contacts to Mg-doped p-GaN grown by MOCVD [1] are studied using a circular transmission line model (TLM) to avoid the need for isolation. For samples which use a p-dopant activation anneal before metallization, no appreciable difference in the specific contact resistance, rc, as a function of different capping options is observed. However, a lower rc is obtained when no pre-metallization anneal is employed, and the post-metallization anneal simultaneously activates the p-dopant and anneals the contact. This trend is shown for Pt/Au, Pt, Pd/Pt/Au, and Ni/Au contacts to p-GaN. The rc 's for these metal contacts are in the range of 1.4–7.6 × 10-3 ohm-cm2 at room temperature at a bias of 10mA. No particular metallization formula clearly yields a consistently superior contact. Instead, the temperature of the contact has the strongest influence.

Detailed studies of the electrical properties of the Pt/Au contacts reveal that the I-V linearity improves significantly with increasing temperature. At room temperature, a slightly rectified I-V characteristic curve is obtained, while at 200°C and above, the I-V curve is linear. For all the p-GaN samples, it is also found that the sheet resistance decreases by an order of magnitude with increasing temperature from 25°C to 350°C. The specific contact resistance is also found to decrease by nearly an order of magnitude for a temperature increase of the same range. A minimum rc of 4.2 × 10-4 ohm-cm2 was obtained at a temperature of 350°C for a Pt/Au contact. This result is the lowest reported rc for ohmic contacts to p-GaN.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 468: Symposium D – Gallium Nitride and Related Materials II , 1997 , 421
Copyright
Copyright © Materials Research Society 1997

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References

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