Investigation of laser-induced-metal phase of MoTe₂ and its contact property via scanning gate microscopy

Abstract

Although semiconductor to metal phase transformation of MoTe2 by high-density laser irradiation of more than 0.3 MW/cm 2 has been reported, we reveal that the laser-induced-metal (LIM) phase is not the 1T′ structure derived by a polymorphic-structural phase transition but consists instead of semi-metallic Te induced by photo-thermal decomposition of MoTe2. The technique is used to fabricate a field effect transistor with a Pd/2H-MoTe2/LIM structure having an asymmetric metallic contact, and its contact properties are studied via scanning gate microscopy. We confirm that a Schottky barrier (a diffusion potential) is always formed at the Pd/2H-MoTe2 boundary and obstacles a carrier transport while an Ohmic contact is realized at the 2H-MoTe2/LIM phase junction for both n-and p-type carriers.

Synthesis of Large-Scale Monolayer 1T′-MoTe2 and Its Stabilization via Scalable hBN Encapsulation

“…As expected, the presence of the hBN layer between the metal contacts and the conductive MoTe 2 induces a tunnel barrier, easily detectable in the nonlinear behavior of the IV characteristics. , A more detailed characterization of the tunneling junction at the interface is reported in Figure S13. From resistance measurements the thickness of the hBN is confirmed to be about 3 or 4 layers, in agreement with AFM characterization (Figure S13a) and previous works employing similar commercially available hBN. , No significant gate dependence is visible in the IV curves shown in Figure a when different back-gates are applied, which was also confirmed in the four-probe transfer curve reported in Figure S12c, suggesting that the MoTe 2 under study has semimetallic behavior, in agreement with previous studies. ,, …”

“…70,71 No significant gate dependence is visible in the IV curves shown in Figure 5a when different back-gates are applied, which was also confirmed in the four-probe transfer curve reported in Figure S12c, suggesting that the MoTe 2 under study has semimetallic behavior, in agreement with previous studies. 14,41,72 The conductivity of the material and its dependence on temperature has further been studied as a function of temperature, from 150 to 380 K, at ambient pressure, in a dry nitrogen atmosphere (more details in the Methods section). In Figure 5b the reduced activation energy, calculated as…”

Signature of Spin-Resolved Quantum Point Contact in p-Type Trilayer WSe2 van der Waals Heterostructure

“…9,10 To date, however, the number of electrostatically induced quantum confinement devices in TMDC or similar 2D materials 7,[11][12][13][14][15][16][17][18] was limited due to their poor crystal quality, mobility, ambient stability, and contact properties. Various methods such as doped or gated graphene contact, 7,17 phase engineering, 19,20 transferred top contact, 21,22 or bottom contact architecture [23][24][25] assembled in glove box was reliably realized for TMDC devices although the quality of low-temperature Ohmic contact is still limited. The Ohmic contact method for p-type material like WSe2 was realized via these methods whereas still high contact resistance and limited to inert atmosphere assembling.…”

Photo-induced Tellurium segregation in $\mathrm{MoTe_2}$

“…The emergent mode at 3.6 THz is considered to be the A 1 mode of tellurium (Te) [30][31][32][33][34] due to segregation of atomic Te from the MoTe 2 samples as a result of surface melting induced by heat-accumulation effects of high repetitive pulsed laser irradiation. The Te segregation observed to date in coherent phonon spectra appearing at 3.6 THz has been occasionally observed in other telluride compounds, such as Ge 2 Sb 2 Te 5 [35], Sb 2 Te 3 [36,37], CdTe [38], ZnTe [39] as well as static-measurement studies on MoTe 2 [18]. On the other hand, additional phonon modes related to the different structural phases were not observed after the laser irradiation: the 2H-to-1T' and 1T'-to-2H phase transitions were not observed.…”

“…Theoretical studies suggest that high-density electronic excitation of the semiconducting 2H phase by light pulses with a photon energy above the band gap can induce a structural phase transition into a metallic 2H * or semi-metallic 1T phase [15][16][17]. However, experimental studies of light-induced structural phase transitions remain controversial: when a strong continuous-wave (CW) laser is used, tellurium segregates from MoTe 2 via photothermal or heat-accumulation effects [18], as surface oxidation in the presence of elevated temperature even under vacuum conditions [19]. On the other hand, there have been few studies of light-induced structural phase transitions in MoTe 2 using femtosecond pulses, for which photo-thermal effects are expected to be significantly less than the case for CW laser irradiation since femtosecond electronic excitation occurs before thermal effects appear [20].…”