Performance tunability of field-effect transistors using MoS2 (1-x) Se2x alloys

Ultra-thin channel materials with excellent tunability of their electronic properties are necessary for the scaling of electronic devices. Two-dimensional materials such as transition metal dichalcogenides (TMDs) are ideal candidates for this due to their layered nature and great electrostatic control. Ternary alloys of these TMDs show composition-dependent electronic structure, promising excellent tunability of their properties. Here, we systematically compare molybdenum sulphoselenide (MoS_2(1-x)Se_2x) alloys, MoS₁Se₁ and MoS_0.4Se_1.6. We observe variations in strain and carrier concentration with their composition. Using them, we demonstrate n-channel field-effect transistors (FETs) with SiO₂ and high-k HfO₂ as gate dielectrics, and show tunability in threshold voltage, subthreshold slope, drain current, and mobility. MoS₁Se₁ shows better promise for low-power FETs with a minimum subthreshold slope of 70 mV/dec, whereas MoS_0.4Se_1.6, with its higher mobility, is suitable for faster operations. Using HfO₂ as gate dielectric, there is an order of magnitude reduction in interface traps and 2x improvement in mobility and drain current, compared to SiO₂. In contrast to MoS₂, the FETs on HfO₂ also display enhancement-mode operation, making them better suited for CMOS applications.