Structural and Electrical Properties of MoTe₂ and MoSe₂ Grown by Molecular Beam Epitaxy

Abstract

We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

Real-time monitoring of 2D semiconductor film growth with optical spectroscopy

“…The thickness and the film structure determined from the morphology revealed by AFM is thus in fully agreement with that deduced from in situ DRS as well as ex situ RBS and Raman spectroscopy measurements. Furthermore, this AFM result is inline with the morphology of MBE MoSe 2 layers grown on Al 2 O 3 (0001) [20] and other substrates [17,21] revealed using aberrationcorrected high-resolution transmission electron microscopy.…”

“…Comparing with the FWHM of the A g 1 peak measured from the mechanically exfoliated 2D MoSe 2 layer, which is around 1cm −1 [30], these numbers are relative larger. This observation suggests the formation of defect rich 2D MoSe 2 layers with relative small grain size [20].…”

“…A large amount of studies have been being carried out to grow large-area, high-quality, singlecrystal 2D-TMDs. Among these efforts, the technologies compatible with the existing microelectronic processes, such as chemical vapor deposition [9,10] and molecular beam epitaxy (MBE) [11][12][13][14][15][16][17][18][19][20][21], are receiving particular attention. On the other hand, real-time monitoring of the growth of 2D-TMD materials has seldom, if ever, been reported.…”

Electron and thermal transport via variable range hopping in MoSe2 single crystals

“…This value is comparable to the value reported in few layer MoSe 2 30,31 . This suggests that the localization length is small and the hence we observe VRH mechanism till room temperature in our experiment 30,32,33 .…”

Transistor properties of exfoliated single crystals of2H−Mo(Se1−xTe<

“…2, where characteristic peaks at 250 and 290 cm −1 are observed in a thin MoSe 2 single crystal, showing that it is a 2H -crystal, as indicated in Ref. [31]. These peaks can be assigned to A 1g and E 2g Raman active modes.…”