Length Scaling of Carbon Nanotube Electric and Photo Diodes down to Sub-50 nm

Carbon nanotubes (CNTs) are promising candidates for future optoelectronics and logic circuits(1-3) Sub-10 nm channel length CNT transistors have been demonstrated with superb performance(4) Yet, the scaling of CNT pn diodes or photodiodes, basic elements for most optoelectronic devices, is held back on a scale of micrometers.5-8 Here, we demonstrate that CNT diodes fabricated via a dopant-free technique show good rectifying characteristics and photovoltaic response even when the channel length is scaled to sub-50 nm. By making a trade-off between performance and size, a diode with both channel length and contact width around 100 nm, fabricated on a CNT with a small diameter (d similar to 1.2 nm), shows a photovoltage of 0.24 V and a fill factor of up to 60%. Study on the dependence of turn-on voltage on scaled channel length reveals transferred charges induced potential barrier at the contact in long channel diodes and the effect of self-adjusting charge distribution. This effect could be utilized for realizing stable and high performance sub-100 nm pitch CNT diodes. As elementary building blocks, such tiny electric and photodiodes could be used in nanoscale rectifiers, photodetectors, light sources, and high-efficiency photovoltaic devices.