Dual Passivation‐Induced n‐Type Doping, Charge Impurity Screening, and Trap Suppression for Achieving High‐Performance and Reliable WS 2 ‐Based Field‐Effect Transistors and Photodetectors

ABSTRACT WS 2 ‐based field‐effect transistors (FETs), photodetectors, and other devices utilizing the back‐gated (BG) architecture are prone to spontaneous oxidation and adsorption of ambient molecules, degrading their performance and reliability. Also, a significantly high contact resistance (R C ) is another bottleneck limiting their performance. This work addresses these issues by using a dual‐layer passivation technique, which enables n‐type doping, charge impurity screening, and trap suppression in WS 2 , boosting the performance and reliability of WS 2 ‐based FETs and photodetectors. Here, the e‐beam‐evaporated Al 2 O 3 is used as the first passivation layer, which, using the density functional theory (DFT) and Raman and photoluminescence (PL) spectra, is found to induce significant n‐type doping in WS 2 . This doping improves the field‐effect mobility (µ FE ) and R C of WS 2 FETs by shielding the electrons in the FET's channel from coulomb impurities and narrowing the Schottky barrier width, respectively. Further, a second passivation layer of a more uniform atomic layer deposition (ALD)‐deposited Al 2 O 3 is used, which assists in providing effective passivation. Using this technique, the µ FE and R C of WS 2 FETs improved by ∼108% and ∼800%, respectively, enhancing their I ON and I ON /I OFF by ∼700% and ∼2 orders, respectively. Moreover, the photocurrent and responsivity of the WS 2 ‐based photodetector improved by around 178 times.