High Performance Hydrogenated Amorphous Silicon n-i-p Photo-diodes on Glass and Plastic Substrates by Low-temperature Fa
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0989-A19-05
High Performance Hydrogenated Amorphous Silicon n-i-p Photo-diodes on Glass and Plastic Substrates by Low-temperature Fabrication Process Kyung Ho Kim1, Yuriy Vygranenko1, Mark Bedzyk2, Jeff Hsin Chang1, Tsu Chiang Chuang1, Denis Striakhilev1, Arokia Nathan3, Gregory Heiler2, and Timothy Tredwell2 1 Electrical and Computer Engineering, Univerity of Waterloo, 200 Univeristy Ave. W, Waterloo, N2L 3G1, Canada 2 Eastman Kodak Company, Rochester, NY, 14652-3487 3 London Centre for Nanotechnology, University College, London, WC1H OAH, United Kingdom
ABSTRACT We report on the fabrication and characterization of hydrogenated amorphous silicon (a-Si:H) films and n-i-p photodiodes on glass and PEN plastic substrates using low-temperature (150 ∫C) plasma-enhanced chemical vapor deposition. Process conditions were optimized for the i-a-Si:H material which had a band gap of ~1.73 eV and low density of states (of the order 1015 cm-3). Diodes with 0.5 µm i-layer demonstrate quantum efficiency ~70%. The reverse dark current of the diodes on glass and PEN plastic substrate is ~10-11 and below 10-10 A/cm2, respectively. We discuss the difference in electrical characteristics of n-i-p diodes on glass and PEN in terms of bulk- and interface-state generation currents. INTRODUCTION There is strong commercial interest at present on the development of thin-film electronics on flexible plastic substrates. Substantial research has been carried out to adopt a-Si:H technology for the fabrication of thin-film semiconductors on plastic. The a-Si:H technology is widely used [1] for industrial production of flat-panel displays, large area imaging devices, and solar energy conversion systems. It conventionally relies on plasma-enhanced chemical vapor deposition (PECVD) of thin film silicon and related alloys on glass substrates with typical process temperatures of 250 ~ 300 ∫C. For the fabrication on plastic substrates, the process temperature often needs to be reduced down to 100 ~ 200 ∫C, and process parameters need to be re-optimized to avoid serious deterioration of material properties. This re-optimization comes at the cost of deposition rate. On the other hand, processing on flexible substrates at reduced temperatures induces less thermal stress in fabricated structures, potentially allowing for thicker films to be deposited and better registration accuracy [2] between device layers. It has been reported that a-Si solar cells [3], thin-film transistors [4], and transistor circuits [5] with good performance characteristics can be fabricated on plastic substrates by plasma deposition at 110 ~ 150 ∫C. In this paper we demonstrate that it is feasible to produce high performance a-Si:H n-i-p photodiodes on plastic substrates using low temperature PECVD.
EXPERIMENTAL PROCEDURE A-Si:H films and n-i-p diode structures were grown at 150 ∫C in a multi-chamber thinfilm deposition system by MVSystems. Undoped a-Si:H layers were deposited from a mixture of silane and hydrogen. To optimize deposition conditions, we varied the silane gas fra
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