Doping-free fabrication of carbon nanotube thin-film diodes and their photovoltaic characteristics |
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Authors: | Qingsheng Zeng Sheng Wang Leijing Yang Zhenxing Wang Zhiyong Zhang Lianmao Peng Weiya Zhou Sishen Xie |
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Affiliation: | 1. Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing, 100871, China 2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
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Abstract: | Random networks of single-walled carbon nanotubes (SWCNTs) were have been grown by chemical vapor deposition on silicon wafers
and used for fabricating field-effect transistors (FETs) using symmetric Pd contacts and diodes using asymmetrical Pd and
Sc contacts. For a short channel FET or diode with a channel length of about 1 μm or less, the device works in the direct
transport regime, while for a longer channel device the transport mechanism changes to percolation. Detailed electronic and
photovoltaic (PV) characterizations of these carbon nanotube (CNT) thin-film devices was carried out. While as-fabricated
FETs exhibited typical p-type transfer characteristics, with a large current ON/OFF ratio of more than 104 when metallic CNTs were removed via a controlled breakdown, it was found that the threshold voltage for the devices was typically
very large, of the order of about 10 V. This situation was greatly improved when the device was coated with a passivation
layer of 12 nm HfO2, which effectively moved the threshold voltages of both FET and diode back to center around zero or turned these device to
their OFF states when no bias was applied on the gate. PV measurements were then made on the short channel diodes under infrared
laser illumination. It was shown that under an illumination power density of 1.5 kW/cm2, the device resulted in an open circuit voltage V
OC = 0.21 V and a short circuit current I
SC = 3.74 nA. Furthermore, we compared PV characteristics of CNT film diodes with different channel lengths, and found that
the power transform efficiency decreased significantly when the device changed from the direct transport to the percolation
regime. |
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