Hydrophobic Polymer Encapsulation Effects on Subgap Density of States in Multilayered Molybdenum Disulfide Field-Effect Transistors

Herein, exfoliated, multilayered molybdenum disulfide (MoS2) (m-MoS2) field-effect transistors (FETs) are implemented with bilayered SiNx/SiOx gate dielectrics on indium tin oxide (ITO) substrates. For a quantitative understanding on gas adsorption effects on the electrical performance of m-MoS2 FETs, subgap density of states (DOSs) in m-MoS2 layers without (or with) hydrophobic polymer encapsulation are extracted using optical charge-pumping capacitance-voltage spectroscopy. Based on extracted subgap DOSs and their deconvolution with analytical model of acceptor (or donor) like states, all electrical parameters are systematically analyzed. More importantly, two times increase in field-effect mobility (μFE) is strongly related with decrease in shallow donor states (NSD) from 2 × 1018 to 2 × 1017 eV−1 cm−3. In addition, significant improvement of subthreshold swing (SS), hysteresis gap (VHYS) are attributed to the reduction of tail states (NTA) from 4 × 1019 to 2 × 1019 eV−1 cm−3, along with decrease in midgap states (NMid) from 3 × 1016 to 1.3 × 1016 eV−1 cm−3. For a final validation, technology computer-aided design (TCAD) simulation with extracted DOS information nicely replicate measured I-V characteristics for m-MoS2 FETs without (or with) encapsulation, indicating that extracted DOS information is quite accurate, compared with implemented m-MoS2 FETs.