Improved Current Density and Contact Resistance in Bilayer MoSe₂ Field Effect Transistors by AlO Capping

Atomically thin semiconductors are of interest for future electronics applications, and much attention has been given to monolayer (1L) sulfides, such as MoS₂, grown by chemical vapor deposition (CVD). However, reports on the electrical properties of CVD-grown selenides, and MoSe₂ in particular, are scarce. Here, we compare the electrical properties of 1L and bilayer (2L) MoSe₂ grown by CVD and capped by sub-stoichiometric AlO. The 2L channels exhibit ∼20× lower contact resistance (R_C) and ∼30× larger current density compared with 1L channels. R_C is further reduced by >5× with AlO capping, which enables improved transistor current density. Overall, 2L AlO-capped MoSe₂ transistors (with ∼500 nm channel length) achieve improved current density (∼65 μA/μm at V_DS = 4 V), a good I_on/I_off ratio of >10⁶, and an R_C of ∼60 kΩ·μm. The weaker performance of 1L devices is due to their sensitivity to processing and ambient. Our results suggest that 2L (or few layers) is preferable to 1L for improved electronic properties in applications that do not require a direct band gap, which is a key finding for future two-dimensional electronics.