Capacitance-voltage analysis of electrical properties for WSe2 field effect transistors with high-k encapsulation layer

Abstract

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.