Temperature-dependent Raman modes of MoS₂/MoSe₂ van der Waals heterostructures

Abstract

Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDs) show extra-ordinary properties compared to their bulk forms, which has inspired a large number of researchers to investigate these materials recently. Design and fabrication of different combinations of 2D TMDs layers can allow for high-performance and novel heterostructure-based devices, of which the performance will depend also on their thermal properties. On the other hand, the temperature-dependent behavior of such heterolayers and their interaction at different temperatures is still not comprehensively studied in a wide temperature range. In this work, we have performed a systematical temperature-dependent (83 K—483 K) Raman spectroscopic analysis of the MoS2/MoSe2 van der Waals (vdW) heterostructures and discussed their stability. After the transfer process of the MoS2 monolayers onto the MoSe2/SiO2/Si, we annealed the samples, which is a commonly used process to increase the crystallinity. Associatively, the thermal annealing process leads to a decrease in the thermal coefficients of the E1 2g and A1g modes of MoS2 and MoSe2 monolayers. Our study shows that the peak positions of the Raman modes in the heterostructures redshift with an increase in temperature. Furthermore, the full width at half maximum (FWHM) of the E1 2g and A1g modes of the layers broaden at higher temperatures. This phenomenon is attributed to increasing phonon–phonon interactions and thermal expansion effects with the ascending temperature. To the best of our knowledge, for the first time, temperature-dependent Raman analysis of MoS2/MoSe2 vdW heterostructures before and after annealing are carried out; and peak positions, FWHMs, and thermal coefficients of the layers are extracted. We do not observe any deformation in the heterobilayer structure even at very low (83 K) or very high temperatures (483 K). This is the first step to confirm the durability of the MoS2/MoSe2 heterolayered devices under extreme temperatures by studying their thermal properties.

An Anti‐Ambipolar Cryo‐Phototransistor

“…The temperature‐induced variation in the full width at half maximum (FWHM) of the observed peaks is attributed to the double‐resonance phenomenon due to phonon dispersion. [ 28 ] Notably, no additional peaks exist in the junction region, clearly pointing out the absence of interlayer vibrations in the p‐ SnS/ n ‐MoSe 2 heterointerface.…”

High‐Performance Te‐Doped PbSe Film Heterojunction Photodetector with Current Rectification Effect and Broadband Detection Capability

“…[ 22 ] The valence band and work function of MoSe 2 are 1.08 eV and 4.23 eV, respectively. [ 20b,21,23 ] As shown in Figure 3f, PbSe 0.5 Te 0.5 has a higher work function and a lower Fermi level compared with MoSe 2 . Therefore, when MoSe 2 is in contact with PbSe 0.5 Te 0.5 , the energy band of PbSe 0.5 Te 0.5 will bend downward, that of MoSe 2 will bend upward, the holes in PbSe 0.5 Te 0.5 will move toward MoSe 2 , and the electrons in MoSe 2 will move toward PbSe 0.5 Te 0.5 .…”

“…It can be observed from the Raman spectrum of MoSe 2 that there are two main peaks at 240 cm −1 and 280 cm −1 , which correspond to the A 1g mode and E 1 2g mode of MoSe 2 , respectively (purple line in Figure 2f). [ 20 ] From the Raman spectrum of PbSe 0.5 Te 0.5 , the peaks at 84 cm −1 and 250 cm −1 are related to lattice phonon (LO) mode and two‐tone scattering (2LO) in PbSe 0.5 Te 0.5 , respectively (orange line in Figure 2f). In the heterojunction region of PbSe 0.5 Te 0.5 /MoSe 2 device, the Raman characteristic peaks of PbSe 0.5 Te 0.5 and MoSe 2 can be clearly observed, which further confirms the excellent uniformity of each component.…”