Role of Hole Trap Sites in MoS₂ for Inconsistency in Optical and Electrical Phenomena

Abstract

Because of strong Coulomb interaction in two-dimensional van der Waals-layered materials, the trap charges at the interface strongly influence the scattering of the majority carriers and thus often degrade their electrical properties. However, the photogenerated minority carriers can be trapped at the interface, modulate the electron-hole recombination, and eventually influence the optical properties. In this study, we report the role of the hole trap sites on the inconsistency in the electrical and optical phenomena between two systems with different interfacial trap densities, which are monolayer MoS-based field-effect transistors (FETs) on hexagonal boron nitride (h-BN) and SiO substrates. Electronic transport measurements indicate that the use of h-BN as a gate insulator can induce a higher n-doping concentration of the monolayer MoS by suppressing the free-electron transfer from the intrinsically n-doped MoS to the SiO gate insulator. Nevertheless, optical measurements show that the electron concentration in MoS/SiO is heavier than that in MoS/h-BN, manifested by the relative red shift of the A Raman peak. The inconsistency in the evaluation of the electron concentration in MoS by electrical and optical measurements is explained by the trapping of the photogenerated holes in the spatially modulated valence band edge of the monolayer MoS caused by the local strain from the SiO/Si substrate. This photoinduced electron doping in MoS/SiO is further confirmed by the development of the trion component in the power-dependent photoluminescence spectra and negative shift of the threshold voltage of the FET after illumination.

High responsivity in MoS2 phototransistors based on charge trapping HfO2 dielectrics

“…There has been a large variation in the reported responsivities 29,30 and even in the dominant photoresponse behavior in SiO 2 -based MoS 2 phototransistors. Some have reported to observing a dominating photogating effect 31 or photoconductive effect 32 . This discrepancy comes from the interface between MoS 2 /SiO 2 where SiO 2 is well known for dangling bonds, which can act as trap sites.…”

High‐Throughput Growth of Wafer‐Scale Monolayer Transition Metal Dichalcogenide via Vertical Ostwald Ripening

“…The obtained n t is related to the quality of the MoS 2 /Al 2 O 3 interfaces, and it is comparable with previously reported values obtained using exfoliated and CVD-grown TMDs. [31][32][33] The narrow distribution of ΔV TH indicates that the quality of the MoS 2 /Al 2 O 3 interface was spatially uniform for the 900 measured devices. A high I on of 1.1 ± 0.1 µA and an extremely low I off of 32.0 ± 3.0 fA were observed, which resulted in a high on/off ratio of 10 7 .…”

Intrinsic Optoelectronic Characteristics of MoS2 Phototransistors via a Fully Transparent van der Waals Heterostructure

“…For instance, vdW heterostructured MoS 2 photodiodes made with tungsten diselenide (WSe 2 ), molybdenum ditelluride (MoTe 2 ), and black phosphorus have been realized to improve photoresponsive characteristics [8][9][10][11][12] . Also, MoS 2 phototransistors with hexagonal boron nitride (h-BN), graphene, and tin diselenide (SnSe 2 ) in a vertical vdW heterostructure have shown enhanced responsivity or faster photoswitching behavior [13][14][15] . Although numerous studies of the optical properties of vdW heterostructured photodetectors have been reported, to date, the intrinsic optical characteristics of atomically thin MoS 2 have not been explored because most previous studies have employed opaque substrates, typically heavily-doped Si with SiO 2 , due to the convenience from a manufacturing perspective.…”

“…under low illumination intensity (Supplementary Figure S6). phototransistors with a vdW heterostructure were realized, a long-lasting photoconductivity was inevitably observed after turning the laser off 13,17,30 ( Figure 5). The origin for the long-lasting photoconductivity in the decay has Our study helps in understanding the intrinsic optoelectronic characteristics of CVD-grown monolayer MoS 2 , and it will provide insight into the realization of 2D materials-based transparent optoelectronics.…”