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 × 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.