Effect of Fabrication Variables on the Performance of Zinc Oxide Metal-Semiconductor-Metal Photodetectors
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1035-L05-04
Effect of Fabrication Variables on the Performance of Zinc Oxide Metal-SemiconductorMetal Photodetectors Tingfang Yen1, Dave Strome2, Sung Jin Kim1, Michael DiNezzaa1, Alexander N. Cartwright1, and Wayne A. Anderson1 1 Electrical Enginnering, State University of New York at Buffalo, 332 Bonner Hall, Buffalo, NY, 14260 2 AMBP Tech Corporation, 201 Circle Drive North, Piscataway, NJ, 08854 ABSTRACT The performance of ZnO metal-semiconductor-metal (MSM) photodetectors can be significantly influenced by modifications in the fabrication process. ZnO thin films were deposited onto silicon substrates by radio frequency magnetron sputtering and later annealed by conventional furnace, rapid thermal anneal or laser anneal. The photoluminescence (PL) analysis revealed that laser annealing at 250 mW/cm2 increased the 370 nm peak from 520 to 1700 a.u. and reduced the defect peak from 380 to 20 a.u. MSM photodetectors were fabricated using an interdigitated and parallel pattern. Values of current responsivity ranged from about 0.025 A/W to above 430 A/W depending upon fabrication conditions and design. INTRODUCTION ZnO could be the ideal potential material for high-speed ultraviolet photodetectors due to its direct wide bandgap and high exciton binding energy of 60 meV. Several papers have discussed the quality improvement by annealing in oxygen 1,2, nitrogen ambient 3, air 4 or vacuum due to reduced defects and enlarged grain size3. Not many papers focus on the effect of laser annealing and the comparison with other annealing methods. Previously, we have studied nitrogen annealing of ZnO samples deposited by RF sputtering and lower power laser annealing of samples deposited by laser assisted molecular beam deposition (LAMBD) 5, and applied those ZnO films to solar cells 6 and metalsemiconductor-metal photodetectors (MSM-PDs) 7,8. In this work, we are studying various annealing techniques, including rapid thermal annealing (RTA) 9, laser annealing (LA), and furnace annealing (FA) in nitrogen atmosphere on ZnO thin films for modifying electrical properties, which will be applied to the MSM-PD. Annealing in nitrogen ambient improves the quality of ZnO and may introduce nitrogen as a dopant. RTA and LA are attractive in terms of quickness, cost and preservation of companion devices or structures. This paper will focus upon higher energy laser annealing and the use of Yb as a contact metal.
EXPERIMENTAL A radio frequency sputtering system has been used for ZnO deposition on various substrates including Si, and Si with SiO2 on the top. The samples with thick SiO2 were prepared for conductivity testing. A 1 inch diameter of ZnO was used as a target, located at around 10 cm from the substrate heated to 4000C. A Ti pump has been used before the sputtering deposition to reduce the moisture and contamination. The ratio of oxygen and argon was controlled while conducting deposition.
After deposition, various annealing steps have been applied to samples; laser annealing with various power levels, furnace annealing with nitrog
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