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Doping effects in devices based on two-dimensional (2D) materials have been widely studied. However, detailed analysis and the mechanism of the doping effect caused by encapsulation layers has not been sufficiently explored. In this work, we present experimental studies on the n-doping effect in WSe2 field effect transistors (FETs) with a high-k encapsulation layer (Al2O3) grown by atomic layer deposition. In addition, we demonstrate the mechanism and origin of the doping effect. After encapsulation of the Al2O3 layer, the threshold voltage of the WSe2 FET negatively shifted with the increase of the on-current. The capacitance-voltage measurements of the metal insulator semiconductor (MIS) structure proved the presence of the positive fixed charges within the Al2O3 layer. The flat-band voltage of the MIS structure of Au/Al2O3/SiO2/Si was shifted toward the negative direction on account of the positive fixed charges in the Al2O3 layer. Our results clearly revealed that the fixed charges in the Al2O3 encapsulation layer modulated the Fermi energy level via the field effect. Moreover, these results possibly provide fundamental ideas and guidelines to design 2D materials FETs with high-performance and reliability.

A polymer template, which has an array of 300 nm diameter pillar patterns, was fabricated by hot embossing method using anodic aluminum oxide (AAO) template as an embossing stamp. After depositing the thin layer of silicon oxide and coating of anti-adhesion monolayer of organic film on silicon oxide, UV nanoimprint lithography was carried out with the polymer template. As a result, nano-pore array pattern, identical to anodic aluminum oxide pattern, was fabricated on silicon substrate. Residual layer of imprinted nano-pore array pattern was removed by oxygen plasma etch and thin film of Au/Ti was deposited. After lift-off process, Au/Ti dot array was also fabricated on silicon substrate.