Tuning the Optoelectronic Properties of Pulsed Laser Deposited “3D”‐MoS2 Films via the Degree of Vertical Alignment of Their Constituting Layers

Abstract Pulsed‐laser‐deposition (PLD) is used to deposit MoS 2 thin films at substrate temperatures ( T d ) ranging from 25 to 700 °C. A T d = 500 °C is identified as the optimal temperature that yields MoS 2 films consisting of highly‐crystallized 2H‐MoS 2 phase with a strong (002) preferential orientation, a direct optical bandgap ( E g ) of ∼1.4 eV and a strong photoresponse of ∼1500%. Raman spectroscopy revealed that the degree of vertical alignment of MoS 2 layers in the films also reaches its maximum at T d = 500 °C. High‐resolution‐transmission‐electron‐microscopy has provided a clear‐cut evidence that the PLD‐MoS 2 films predominantly consist of vertically aligned MoS 2 layers over all the film thickness of ∼90 nm, enabling those “3D” films to behave as a direct‐bandgap “2D‐MoS 2 ” with exceptional optoelectronic properties. Indeed, at T d = 500 °C, the PLD‐MoS 2 based photodetectors (PDs) devices are shown to exhibit the highest responsivity ( R ) and detectivity ( D *) values (125 mA W −1 and 9.2 × 10 9 Jones, respectively) ever reported for large area (≥ 1 cm 2 ) MoS 2 ‐based PDs operating at a voltage as low as 1 V. For the first time, a constant‐plus‐linear relationship between E g , R , and D * of the PDs and the degree of vertical alignment of the MoS 2 layers is established. Such a correlation is fundamental for the controlled growth of PLD‐MoS 2 films and the tuning of their properties in view of their integration with standard large‐scale‐integration processing.