SURFACE AND CONTACT ENGINEERING OF TWO-DIMENSIONAL MATERIALS ENABLED HIGH PERFORMANCE ELECTRONIC AND OPTOELECTRONIC DEVICES

Abstract

Two-dimensional (2D) materials have been rapidly established as promising building blocks for versatile atomic-scale circuits and multifunctional devices. However, the high contact resistance in 2D materials based transistors seriously hinders their applications in complementary electronics. Therefore, it is crucial to regulate and optimize the properties of the electrical contacts in 2D materials-based devices. In this thesis, we firstly find that Cs surface modification stimulates a semiconductor to metal (2H to 1T’) phase transition in WSe2. Secondly, we show that an ohmic homojunction n-type WSe2 transistor is realized through spatially controlling the Cs doping region near the contacts. Our method significantly optimizes the WSe2 transport behavior with a perfect low subthreshold swing of ~61 mV/dec and an ultrahigh current on/off ratio exceeding ~10^9. We elucidate that the ideal n-type behavior originates from the negligible Schottky barrier height of ~9.4 meV and low contact resistance of ~4.3 kΩ μm in the 2H-1T’ homojunction device. Thirdly, with the surface functionalization by aluminum, few-layer black phosphorus exhibits improved electron mobility together with increased photoresponse. In conclusion, our findings envision surface and contact the engineering of 2D materials enabled high performance complementary electronic devices.