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High Sensitivity of Hydrogen Sensing Through N-polar GaN Schottky Diodes

Published online by Cambridge University Press:  31 January 2011

Yu-Lin Wang
B.H. Chu
Affiliation:, University of Florida, Gainesville, Florida, United States
Chih-Yang Chang
Affiliation:, University of Florida, Gainesville, Florida, United States
Ke Hung Chen
Affiliation:, University of Florida, Gainesville, Florida, United States
Yu Zhang
Affiliation:, Yale, New Haven, Connecticut, United States
Qian Sun
Affiliation:, Yale, New Haven, Connecticut, United States
Jung Han
Affiliation:, Yale, New Haven, Connecticut, United States
S.J. Pearton
Affiliation:, Univ.Florida, Materials, PO Box 116400, Gainesville, Florida, 32611, United States
F Ren
Affiliation:, University of Florida, Chemical Engineering, Gainesville, Florida, United States
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N-polar and Ga-polar GaN grown on c-plane sapphire by a metal-organic chemical vapor deposition (MOCVD) system were used to fabricate platinum deposited Schottky contacts for hydrogen sensing at room temperature. Wurtzite GaN is a polar material. Along the c-axis, there are N-face (N-polar) or Ga-face (Ga-polar) orientations on the GaN surface. The Ohmic contacts were formed by lift-off of e-beam deposited Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (1200 Å). The contacts were annealed at 850°C for 45 s under a flowing N2 ambient. Isolation was achieved with 2000 Å plasma enhanced chemical vapor deposited SiNx formed at 300°C. A 100 Å of Pt was deposited by e-beam evaporation to form Schottky contacts. After exposure to hydrogen, Ga-polar GaN Schottky showed 10% of current change, while the N-polar GaN Schottky contacts became fully Ohmic. The N-polar GaN Schottky diodes showed stronger and faster response to 4% hydrogen than that of Ga-polar GaN Schottky diodes. The abrupt current increase from N-polar GaN Schottky exposure to hydrogen was attributed to the high reactivity of the N-face surface termination. The surface termination dominates the sensitivity and response time of the hydrogen sensors made of GaN Schottky diodes. Current-voltage characteristics and the real-time detection of the sensor for hydrogen were investigated. These results demonstrate that the surface termination is crucial in the performance of hydrogen sensors made of GaN Schottky diodes.

Research Article
Copyright © Materials Research Society 2010

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