Light induced tunnel effect in CNT-Si photodiode

Negative differential resistance (NDR), for which the current is a decreasing function of the voltage, has been observed in the current-voltage curves of several types of structures. We measured tunnelling current and NDR by illuminating large area heterojunction obtained by growing Multi Wall Carbon Nanotubes on the surface of n-doped Silicon substrate. In the absence of light, the current flow is null until a junction threshold of about 2.4. V is reached, beyond which the dark current flows at room temperature with a very low intensity of few nA. When illuminated, a current of tens nA is observed at a drain voltage of about 1.5. V. At higher voltage the current intensity decreases according to a negative resistance of the order of MΩ. In the following we report details of tunneling photodiode realized and negative resistance characteristics.