Channel-length-dependent transport and photovoltaic characteristics of carbon-nanotube-based, barrier-free bipolar diode.

Carbon nanotube (CNT) diodes with different channel length between L = 0.6 μm to 3.5 μm are fabricated on the same tube, and the electric and photovoltaic characteristics are investigated. It is found that although the open voltage of the diode increases rapidly for channel length L less than 1.0 μm, it saturates for longer channel devices. On the other hand, the short circuit current of the diode exhibites a clear peak at intermediate channel length of about 1.5 μm, a large leakage current via tunneling for short channel device and significantly decreased current for long channel device due to the increased recombination and channel resistance. The optimal channel length for a CNT diode in photovoltaic application is thus determined to be about 1.5 μm.