Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices___________________________________________________________

Tzu-Yung Huang1,, Yu Song1, Rajaram Bhat2, Chung-En Zah2, and Claire F. Gmachl1

1 Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA2 Corning Inc., Corning, NY 14831, USA

Work supported by PEI Grand Challenges Program

Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices

• Quantum Cascade Lasers are used widely in trace gas sensing applications

• III-Nitride materials have potential to achieve QCLs with emission wavelengths below 3µm, opening us up to a wider range of chemicals (C-H stretch vibration)

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Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices

• So far, the overall high electrical resistance causes the device to heat up, precluding any emission

• We tried several recipes varying Titanium thickness while keeping Al/Ni/Au overlay thickness constant, and found the best results at 6nm (25Ω)

• We also optimized the annealing recipe, having the best results at 800°C for 80s

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Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices___________________________________________________________

-But hold on, are we sure that all ofthat is from the electrical contacts?

A B C D E F G

Ti 6nm -----Ti10nm-----Ti40nm-----

Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices

• To answer our question: we varied the gap distance between the outer and inner contact as well as the contact size

• What we found: the average sheet resistance is 748.5Ω! While the specific contact resistivity is only 2.87e-4Ω

• Our metal contacts weren’t the main culprit! Now we can make a new emitter sample with a new design

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Corrected Total Resistance vs. Gap Distance for inner contact size 400 µm

20 40 60

40

60

Cor

rect

ed T

otal

Res

ista

nce

(Ohm

s)

Gap Distance (Microns)

Corrected Total Resistance (Ohms) Linear Fit Corrected Total Resistance

Rsh: 842.15Ωρc: 3.43e-4Ω

Different contact sizes with varying gap spacing

Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices

Summary• Discover source of high device resistance• Measured sheet and specific contact resistance

Conclusion• Extensive work experience in the clean room• Further understanding of Quantum Cascade Lasers and other

related semiconductor devices that can be used for environmental applications

• Results presented at MIRTHE Summer Workshop• Co-Author of conference paper to ITQW 2013• Will co-author journal publication• Continuation of the project during the school year• Provided insights into post graduation plans

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Improvement on Ti/Al/Ni/Au Electrical Contacts on GaN/AlGaN Superlattices

Thank You!

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