Large-area synthesis of monolayer WSe₂ on a SiO₂/Si substrate and its device applications

Abstract

Recently two-dimensional layered semiconductors with promising electronic and optical properties have opened up a new way for applications in atomically thin electronics and optoelectronics. Here we report a large-area growth of monolayer WSe2 directly on SiO2/Si substrates by a chemical vapor deposition (CVD) method under atmospheric pressure. A sub-cooling step was demonstrated to have a key role in achieving this large-area growth. The monolayer configuration of the as-grown WSe2 was proven by spherical-aberration-corrected high resolution scanning transmission electron microscopy (HRSTEM), atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) spectroscopy. P-type behavior of as-grown monolayer WSe2 with a mobility of ∼0.2 cm(2) V(-1) s(-1) and a carrier concentration of 1.11 × 10(18) cm(-3) was confirmed using back-gated field effect transistor (FET) devices. This large-area growth directly on a SiO2/Si substrate provides a new way to meet the industrial manufacturing requirements.

Ultrafast Self-Limited Growth of Strictly Monolayer WSe2Crystals

“…The FFT filtered image (Figure i) of a small region marked in Figure h was shown to detail the atomic structure of the crystal. The lattice constant was measured to be about 0.325 nm, which was in accordance with the previous reports . We also carried out the HRTEM‐based defect statistics at randomly selected domains and the defect density up to (1.4 ± 0.46) × 10 –13 cm –2 is found (Figure S1, Supporting Information).…”

“…Thus the formation of WSe 2 is a thermodynamically dominant surface reaction process and subsequently tends to aggregate into amorphous structures instead of crystals with high crystalline, which is aggravated by their extremely strong surface tension and poor wettability over the substrate. Several approaches had been developed to fabricate WSe 2 crystals by utilizing low pressure or employing high‐vapor‐pressure precursors to improve the mass‐transport process so as to weaken the influence of the thermodynamic factor and optimize the deposition efficiency . However, the presence of multilayers is still unavoidable and the root cause lies in the lack of significantly energetically favorable competition between layer accumulation and size expansion, which cannot be solved by only adjusting the dynamic mass transport process.…”

Anomalous photoluminescence thermal quenching of sandwiched single layer MoS_2

“…15 E and A 1g phonon modes is observed to be 19.5 ± 0.5 cm −1 , which reveals that the sandwiched MoS 2 layer deposited by CVD is a single-layer [24,25]. Fig.…”

Large-area highly crystalline WSe_2 atomic layers for ultrafast pulsed lasers

“…All WSe 2 layers reveal two characteristic peaks located at 252 cm −1 and 262 cm −1 , which are assignable to the in-plane E 2g 1 mode and out-of-plane A 1g mode (insert of Fig. 2(e)), respectively [28,31]. Note that the Raman peak B 2g 1 mode at 309 cm −1 is attributed to the interlayer interactions [31].…”

“…Unlike MoS 2 , large-area atomic-layered WSe 2 for optoelectronic devices yet remains a significant challenge as the chemical reactivity of selenium is much lower than that of sulfur. The CVD method has been recently presented for synthesis of large-scale WSe 2 films by introducing hydrogen as a strong reducer during the synthesis reaction [19,27,28]. The excellent electronic characteristics of large-area WSe 2 films such as mobility of 350 cm 2 v −1 s −1 and on/off ratio of 10 8 have been studied in electronic devices [19], while their nonlinear optical properties and the potential applications in ultrafast photonics have remained elusive.…”