“…The highly crystalline structure (Fig. 4b), as well as the narrow E 1 2g Raman peak (a FWHM of 5.7 cm −1 ) and the sharp PL emission (a FWHM of 49 meV) without the defect emission at 1.54 eV 7,8,25,44 , indicate high quality of the CVD-WSe 2 samples grown on the ne-PECVD 2D-BN.Fig. 4Direct growth of CVD-WSe 2 on two-dimensional hexagonal-boron nitride (2D-BN).…”
Relatively low mobility and thermal conductance create challenges for application of tungsten diselenide (WSe2) in high performance devices. Dielectric interface is of extremely importance for improving carrier transport and heat spreading in a semiconductor device. Here, by near-equilibrium plasma-enhanced chemical vapour deposition, we realize catalyst-free growth of poly-crystalline two-dimensional hexagonal-boron nitride (2D-BN) with domains around 20~ 200 nm directly on SiO2/Si, quartz, sapphire, silicon or SiO2/Si with three-dimensional patterns at 300 °C. Owing to the atomically-clean van-der-Walls conformal interface and the fact that 2D-BN can better bridge the vibrational spectrum across the interface and protect interfacial heat conduction against substrate roughness, both improved performance and thermal dissipation of WSe2 field-effect transistor are realized with mobility around 56~ 121 cm2 V−1 s−1 and saturated power intensity up to 4.23 × 103 W cm−2. Owing to its simplicity, conformal growth on three-dimensional surface, compatibility with microelectronic process, it has potential for application in future two-dimensional electronics.
“…The highly crystalline structure (Fig. 4b), as well as the narrow E 1 2g Raman peak (a FWHM of 5.7 cm −1 ) and the sharp PL emission (a FWHM of 49 meV) without the defect emission at 1.54 eV 7,8,25,44 , indicate high quality of the CVD-WSe 2 samples grown on the ne-PECVD 2D-BN.Fig. 4Direct growth of CVD-WSe 2 on two-dimensional hexagonal-boron nitride (2D-BN).…”
Relatively low mobility and thermal conductance create challenges for application of tungsten diselenide (WSe2) in high performance devices. Dielectric interface is of extremely importance for improving carrier transport and heat spreading in a semiconductor device. Here, by near-equilibrium plasma-enhanced chemical vapour deposition, we realize catalyst-free growth of poly-crystalline two-dimensional hexagonal-boron nitride (2D-BN) with domains around 20~ 200 nm directly on SiO2/Si, quartz, sapphire, silicon or SiO2/Si with three-dimensional patterns at 300 °C. Owing to the atomically-clean van-der-Walls conformal interface and the fact that 2D-BN can better bridge the vibrational spectrum across the interface and protect interfacial heat conduction against substrate roughness, both improved performance and thermal dissipation of WSe2 field-effect transistor are realized with mobility around 56~ 121 cm2 V−1 s−1 and saturated power intensity up to 4.23 × 103 W cm−2. Owing to its simplicity, conformal growth on three-dimensional surface, compatibility with microelectronic process, it has potential for application in future two-dimensional electronics.
“…This emission difference cannot be observed by optical or AFM measurements. PL emission in monolayer TMDCs crystal is usually nonuniform and has been observed quite a few times in both CVD-grown [21–23, 51–53] and mechanically exfoliated layers [24, 54–56]. The main causes of nonuniform PL emission include lattice defects (including impurities [56, 57] and vacancies [27]), localized electronic states [52, 58], strain [43], and edge effect [22].…”
Section: Resultsmentioning
confidence: 99%
“…3. The obtained PL spectra from center position is deconvoluted into three peaks: neutral exciton at ~ 1.624 eV (marked as A) [51, 52], trion at 1.60 eV (marked as A + ) [29, 52], and an unknown emission peak (marked as D) around 1.53 eV (the detailed fitting basis are shown in Additional file 1: Figures S6–S8). Figure 3b shows the PL emission is dominated by the A + in the center position.…”
Bottom-up epitaxy has been widely applied for transition metal dichalcogenides (TMDCs) growth. However, this method usually leads to a high density of defects in the crystal, which limits its optoelectronic performance. Here, we show the effect of growth temperature on the defect formation, optical performance, and crystal stability in monolayer WSe
2
via a combination of Raman and photoluminescence (PL) spectroscopy study. We found that the defect formation and distribution in monolayer WSe
2
are closely related to the growth temperature. These defect density and distribution can be controlled by adjusting the growth temperature. Aging experiments directly demonstrate that these defects are an active center for the decomposition process. Instead, monolayer WSe
2
grown under optimal conditions shows a strong and uniform emission dominated by neutral exciton at room temperature. The results provide an effective approach to optimize TMDCs growth.
Electronic supplementary material
The online version of this article (10.1186/s11671-019-3110-z) contains supplementary material, which is available to authorized users.
“…Wu et al studied the effects of defects on the device transmission performance in monolayer WSe 2 tunneling field-effect transistors (TFSTs) by performing the ab initio calculation, which indicates that defects can be well designed to obtain high-performance TFETs [25]. Meanwhile, structural defects were found in the as-grown 2D materials due to the imperfection of the growth process [19, 20, 26–28]. For example, intrinsic structural defects, such as point defects, are noticeable in the as-grown monolayer WSe 2 [26].…”
Section: Introductionmentioning
confidence: 99%
“…Meanwhile, structural defects were found in the as-grown 2D materials due to the imperfection of the growth process [19, 20, 26–28]. For example, intrinsic structural defects, such as point defects, are noticeable in the as-grown monolayer WSe 2 [26].…”
By adopting the first-principle methods based on the density functional theory, we studied the structural, electronic, and magnetic properties of defected monolayer WSe
2
with vacancies and the influences of external strain on the defected configurations. Our calculations show that the two W atom vacancies (V
W2
) and one W atom and its nearby three pairs of Se atom vacancies (V
WSe6
) both induce magnetism into monolayer WSe
2
with magnetic moments of 2 and 6 μ
B
, respectively. The magnetic moments are mainly contributed by the atoms around the vacancies. Particularly, monolayer WSe
2
with V
W2
is half-metallic. Additionally, one Se and one W atom vacancies (V
Se
, V
W
), two Se atom vacancies (V
Se-Se
), and one W atom and the nearby three Se atoms on the same layer vacancy (V
WSe3
)-doped monolayer WSe
2
remain as non-magnetic semiconducting. But the impure electronic states attributed from the W d and Se p orbitals around the vacancies locate around the Fermi level and narrow down the energy gaps. Meanwhile, our calculations indicate that the tensile strain of 0~7% not only manipulates the electronic properties of defected monolayer WSe
2
with vacancies by narrowing down their energy gaps, but also controls the magnetic moments of V
W
-, V
W2
-, and V
WSe6
-doped monolayer WSe
2
.
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