Characterization of Radiation Damage in Carbon Nanotube Field-Effect Transistors

Carbon nanotube field-effect transistors with
${\rm Al}_{2}{\rm O}_{3}$
gate dielectrics have been characterized before and after 1 MeV electron irradiation. Pre-irradiation interface trap densities determined by charge pumping measurements were on the order of
$10^{11}~\hbox{cm}^{\hbox{-}2}\hbox{eV}^{\hbox{-}1}$
. Following irradiation to fluences of
$10^{16}~\hbox{e/cm}^2$
and
$10^{17}~\hbox{e/cm}^2$
, the measured interface trap densities decreased significantly for all devices. This result is largely attributed to the removal of molecular adsorbates that act as trap sites on the nanotubes (de-doping) while the devices are irradiated under vacuum. Negative shifts in the transistor
$I\hbox{-}V$
curves with irradiation indicate radiation-induced hole trapping in the gate dielectric, with some recovery after room temperature annealing. No significant changes were observed in the Raman spectra following irradiation, indicating the intrinsic structure of the carbon nanotubes remained unchanged. These results suggest that the radiation response of these devices is dominated by charge trapping in the oxide layers and at the carbon nanotube surfaces. Furthermore, the charge pumping technique can be used as a tool for probing surface adsorbates in carbon nanotube devices, and elucidating their role in the device radiation response.