Cotunneling assisted internal relaxation transport in the dopant atom transistor*

In the recent years, the dopant atom based devices have been investigated for pratical applications. One important aspect of these devices is the cotunneling current which is observed in the Coulomb blockade regime and limits the device performance. Since Coulomb blockade supresses sequential tunnelling of the electrons there exist some higher order tunnelling process that goes by virtual state of the dopant.

A uniformly doped narrow-channel SOI-FET  fabricated device with average doping concentration 1×10¹⁸ cm^-3 and thickness ~5 nm is studied at 5.5 K temperature. The Coulomb blockade transport through different dopant atoms are observed in this device. Apart from first-order tunneling, second-order tunneling is also observed inside the Coulomb blockade regime. We have identified the position of excited states in the stability diagram. The region of cotunneling regime is connected to the excited state in the non-blockade region. The observed cotunneling is inelastic in nature as it occurred at V_D ≥ 2ΔE/e, where ΔE is the energy difference between ground state and excited state of the dopant. The observed cotunneling features are internally relaxed through excited state of the dopant. The present observation would help us to understand the cotunneling followed by internal relaxation in the dopant atom device.