Heteroepitaxial Growth of High Optical Quality, Wafer-Scale van der Waals Heterostrucutres

Abstract

Transition metal dichalcogenides (TMDs) are materials that can exhibit intriguing optical properties like a change of the bandgap from indirect to direct when being thinned down to a monolayer. Well-resolved narrow excitonic resonances can be observed for such monolayers although only for materials of sufficient crystalline quality and so far mostly available in the form of micrometer-sized flakes. A further significant improvement of optical and electrical properties can be achieved by transferring the TMD on hexagonal boron nitride (hBN). To exploit the full potential of TMDs in future applications, epitaxial techniques have to be developed that not only allow the growth of large-scale, highquality TMD monolayers but also allow the growth to be performed directly on large-scale epitaxial hBN. In this work, we address this problem and demonstrate that MoSe 2 of high optical quality can be directly grown on epitaxial hBN on an entire 2 in. wafer. We developed a combined growth theme for which hBN is first synthesized at high temperature by metal organic vapor phase epitaxy (MOVPE) and as a second step MoSe 2 is deposited on top by molecular beam epitaxy (MBE) at much lower temperatures. We show that this structure exhibits excellent optical properties, manifested by narrow excitonic lines in the photoluminescence spectra. Moreover, the material is homogeneous on the area of the whole 2 in. wafer with only ±0.14 meV deviation of excitonic energy. Our mixed growth technique may guide the way for future large-scale production of high quality TMD/hBN heterostructures.

Molecular Beam Epitaxy growth of MoTe$_{\tiny{\textrm{2}}}$ on Hexagonal Boron Nitride

“…From our previous work on MBE growth of MoSe 2 on hBN [25,26] we concluded that annealing of the samples after the growth helps to achieve continuous and smooth area of the first TMDC monolayer. The panels d)-f) of Fig.…”

Macroscopic transition metal dichalcogenides monolayers with uniformly high optical quality

“…To obtain larger area monolayers, epitaxial growth 17 , 18 and exfoliation by metal tapes 19 – 21 have been developed. Yet epitaxial TMD monolayers typically are polycrystalline, have high defect densities, large spatial inhomogeneities, and broad emission linewidths 17 , 18 .…”

van der Waals epitaxy of transition metal dichalcogenides via molecular beam epitaxy: looking back and moving forward

“…3(l–o)). 99 Recently, Wei et al 100 have shown the complex nature of the nucleation and growth processes of MoSe 2 monolayers grown via MBE on mica. It has been observed that the 1T phase of MoSe 2 forms along with a comparable quantity of the 2H phase of MoSe 2 , where the 1T phase converts gradually into the stable 2H phase before the complete growth of the first monolayer.…”

“…95 In a recent report, He et al 96 wafer through an in-depth examination of the optical studies (Figure 3(l-o)). 99 Recently, Wei et al 100…”