Electrode- Induced Self- Healed Monolayer MoS2 for High Performance Transistors and Phototransistors

Abstract

Contact engineering for monolayered transition metal dichalcogenides (TMDCs) is considered to be of fundamental challenge for realizing high- performance TMDCs- based (opto) electronic devices. Here, an innovative concept is established for a device configuration with metallic copper monosulfide (CuS) electrodes that induces sulfur vacancy healing in the monolayer molybdenum disulfide (MoS2) channel. Excess sulfur adatoms from the metallic CuS electrodes are donated to heal sulfur vacancy defects in MoS2 that surprisingly improve the overall performance of its devices. The electrode- induced self- healing mechanism is demonstrated and analyzed systematically using various spectroscopic analyses, density functional theory (DFT) calculations, and electrical measurements. Without any passivation layers, the self- healed MoS2 (photo)transistor with the CuS contact electrodes show outstanding room temperature field effect mobility of 97.6 cm2 (Vs)- 1, On/Off ratio > 108, low subthreshold swing of 120 mV per decade, high photoresponsivity of 1 à 104 A W- 1, and detectivity of 1013 jones, which are the best among back- gated transistors that employ 1L MoS2. Using ultrathin and flexible 2D CuS and MoS2, mechanically flexible photosensor is also demonstrated, which shows excellent durability under mechanical strain. These findings demonstrate a promising strategy in TMDCs or other 2D material for the development of high performance and functional devices including self- healable sulfide electrodes.A novel sulfide electrode system allows sulfur- vacancy self- healing in 2D MoS2. Ultrathin CuS electrode heals defects in the MoS2 channel spontaneously upon mild thermal annealing. The self- healed CuS/MoS2 transistors and phototransistors show impressive device performance.