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Electric and Morphology Studies of Ohmic Contacts on AlGaN/GaN

Published online by Cambridge University Press:  15 March 2011

V. Tilak
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
R. Dimitrov
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
M. Murphy
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
B. Green
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
J. Smart
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
W.J. Schaff
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
J.R. Shealy
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
L.F. Eastman
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY -14850
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Abstract

AlGaN/GaN is a promising system for high power electron devices. Quality of ohmic contacts is a critical parameter in determining the performance of the device. Although we have achieved a transfer resistance (Rc) of 0.35Δmm and ρc of 9.5×10−7 Δcm−2 the morphology and edge acuity of the contacts are poor. The standard ohmic contact recipes consist of a combination of Titanium and Aluminum with Nickel and/or Gold. This is annealed at 800°C-950°C [1-5]. In this work we study ohmic contacts on unintentionally doped Al0.3Ga0.7N/GaN system. We look at ratios of Ti/Al from 0 to 2 to determine which is the optimum ratio in terms of surface morphology and electrical characteristics. From our studies we conclude that morphology of a Ti/Al contact is good over a ratio of 0.3 and the contact resistance is minimized at a Ti/Al of 0.6. The ohmic contacts are improved electrically if a layer of gold is added on top. The best electrical contacts however were obtained with a four layer recipe of Ti/Al/Ti/Au, which gave contact resistance (Rc) around 0.45Δmm, but the morphology of the contacts was poor.

Type
Research Article
Copyright
Copyright © Materials Research Society 2000

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References

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