Controlling the electronic properties of SWCNT FETs via modification of the substrate surface prior to atomic layer deposition of 10 nm thick Al ₂O₃ film

We demonstrate the controllability of the electronic transport properties of single-walled carbon nanotube (SWCNT) field effect transistors (FETs) via the use of 10 nm thick atomic-layer-deposited aluminum oxide (Al₂O ₃) gate dielectric films, where the substrate surfaces were modified with differently functionalized self-assembled monolayers (SAMs) prior to their growth, namely SAMs with hydrophobic (-CH₃) or hydrophilic (-OH) groups. Al₂O₃ grown on a hydrophilic surface causes the SWCNT FETs to keep their intrinsic p-type transfer characteristics by alleviating the electron-doping effect originating from defects in the Al ₂O₃ film. However, the SAM with methyl groups increases the defect density of the Al₂O₃ film, enhancing the n-type transfer characteristics and inducing ambipolar to n-type behavior in the SWCNT FETs. In this work, we find clues about the distribution of charged defects in the Al₂O₃ film, which strongly influences the transfer characteristics of the SWCNT FETs, by measuring the thickness-dependent flat band voltages.