High sensitivity of hydrogen sensing through N-polar GaN Schottky diodes
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1202-I06-06
High sensitivity of hydrogen sensing through N-polar GaN Schottky diodes Yu-Lin Wang1, B. H. Chu2, C.Y. Chang2, K. H. Chen2, Y. Zhang3, Q. Sun3, J. Han3, S. J. Pearton1, and F. Ren2 1 Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 2 Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, 3 Department of Electrical Engineering, Yale University, New Haven, CT 06520, USA ABSTRACT 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. INTRODUCTION There is great interest in detection of hydrogen sensors for use in hydrogen-fuelled automobiles and with proton-exchange membrane (PEM) and solid oxide fuel cells for space craft and other long-term sensing applications. These sensors are required to detect hydrogen near room temperature with minimal power consumption and weight and with a low rate of false alarms. Due to their low intrinsic carrier concentrations, GaN- and SiC-based wide band gap semiconductor sensors can be operated at lower current levels than conventional Si-based devices and offer the capability of detection to 600 °C [1-10]. The ability of electronic devices fabricated in these materials to function in high temperature, high power and high flux/energy radiation conditions enable performance enhancements in a wide variety of spacecraft, satellite, homeland defense, mining, automobile, nuclear power, and radar applications. Wurtzite GaN is a polar material. Therefore, along the c-axis, there are N-face (N-polar) or Ga-face (Ga-polar) orientations on the GaN surface. The polarity determined by the GaN surface has been used t
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