Charge transport in MBE-grown 2H-MoTe2bilayers with enhanced stability provided by an AlOxcapping layer

Thin layers of transition metal dichalcogenides have been intensively studied over the last few years due to their novel physical phenomena and potential applications. One of the biggest problems in laboratory handling and moving on to application-ready devices lies in the high sensitivity of their physicochemical properties to ambient conditions. We demonstrate that novel,in situcapping with an ultra-thin, aluminum film efficiently protects thin MoTe(2)layers stabilizing their electronic transport properties after exposure to ambient conditions. The experiments have been performed on bilayers of 2H-MoTe(2)grown by molecular beam epitaxy on large area GaAs(111)B substrates. The crystal structure, surface morphology and thickness of the deposited MoTe(2)layers have been precisely controlledin situwith a reflection high energy electron diffraction system. As evidenced by high resolution transmission electron microscopy, MoTe(2)films exhibit perfect arrangement in the 2H phase and the epitaxial relation to the GaAs(111)B substrates. After the growth, the samples werein situcapped with a thin (3 nm) film of aluminum, which oxidizes after exposure to ambient conditions. This oxide serves as a protective layer to the underlying MoTe2. Resistivity measurements of the MoTe(2)layers with and without the cap, exposed to low vacuum, nitrogen and air, revealed a huge difference in their stability. The significant rise of resistance is observed for the unprotected sample while the resistance of the protected one is constant. Wide range temperature resistivity studies showed that charge transport in MoTe(2)is realized by hopping with an anomalous hopping exponent ofx similar or equal to 0.66, reported also previously for ultra-thin, metallic layers.