Band alignment at interfaces of synthetic few-monolayer MoS2 with SiO2 from internal photoemission

Abstract

Electron band alignment at interfaces of SiO2 with directly synthesized few-monolayer (ML) thin semiconducting MoS2 films is characterized by using field-dependent internal photoemission of electrons from the valence band of MoS2 into the oxide conduction band. We found that reducing the grown MoS2 film thickness from 3 ML to 1 ML leads to ≈400 meV downshift of the valence band top edge as referenced to the common energy level of the SiO2 conduction band bottom. Furthermore, comparison of the MoS2 layers grown by a H-free process (sputtering of Mo in sulfur vapor) to films synthesized by sulfurization of metallic Mo in H2S indicates a significant (≈500 meV) electron barrier increase in the last case. This effect is tentatively ascribed to the formation of an interface dipole due to the interaction of hydrogen with the oxide surface.

Direct Evidence of Electronic Interaction at the Atomic-Layer-Deposited MoS2 Monolayer/SiO2 Interface

“…It follows that the contributions of S 2-(p 6 ) appear at higher BEs is in contrast to the common belief that the influence of the vdW interaction between the semiconducting MoS 2 and highly insulating SiO 2 on the electronic structure is negligible [19,48]. However, there have been reports that certain charge trapping can occur in SiO 2 layers in the vicinity of MoS 2 [49,50], which might imply that electron hopping among adjacent S-O ions is feasible.…”

Energy Band Alignment of a Monolayer MoS2 with SiO2 and Al2O3 Insulators from Internal Photoemission

“…Results of the quality assessment of these layers using XPS and other methods are reported elsewhere . For the IPE experiments described in the present work, the 1 ML MoS 2 /insulator/p–Si(100) structures were completed with optically non‐transparent (approximately 100 nm‐thick) Al contact pads to ensure reliable electrical contact to the ML MoS 2 , while blanket a Al layer on the silicon wafer backside served as the back contact (Figure ). The Al contact pads were evaporated thermo‐resistively through a shadow mask to exclude damage or contamination of the MoS 2 film.…”

“…Similarly, investigation of van der Waals epitaxial layers of SnS 2 and SnSe 2 on chalcogenide single crystals (WSe 2 , MoS 2 , MoTe 2 , GaSe) suggests the validity of EAR as neither structural nor chemical dipoles contribution to band offsets has been encountered . However, the recently revealed impact of the MoS 2 synthesis chemistry or the layer transfer processing on band alignment with insulating SiO 2 suggests a less ideal picture, pointing significant additional influences.…”

Determination of energy thresholds of electron excitations at semiconductor/insulator interfaces using trap-related displacement currents

“…The GaN/Al2O3 samples were prepared on heavily doped n-type (n≈1x10 18 cm -3 ) 2 m precursors, respectively, following the chemical vapor deposition (CVD) process described elsewhere [5]. Electrical contact to the disulfide semiconductor layers was done either by using non-transparent contact pads (Au or Al, 100 nm thick) [4,6] or by evaporation of semitransparent (15 nm) Au or Al electrodes of 0.5 mm 2 area. Back contact to Si substrate was fabricated by evaporation of 100-nm thick blanket Al layer.…”

“…Obviously, both PC and IPE can also be observed using more conventional dc current measurements using the same measurement arrangement illustrated in Fig. 1(b) [3,4]. However, the dc photocurrent measurements are often impaired by leakage current or by high layer resistance as it happen in the case of fewmonolayer (ML) thin films.…”