Zuzanna Ogorzalek1,Adam Kwiatkowski1,Krzysztof Korona1,Slawomir Kret2,Krzysztof Morawiec2,Johannes Binder1,Dariusz Wasik1,Jakub Polaczynski2,Bartlomiej Seredynski1,Janusz Sadowski1,2,3,Wojciech Pacuski1,Marta Gryglas-Borysiewicz1
University of Warsaw1,Institute of Physics PAS2,Lund University3
MoTe
2 belongs to transition metal dichalcogenides - materials, which have been intensively studied for the last few years. They provide a rare occasion to test relativistic physics with low energy excitations in condensed matter experiments. The unusual properties of the charge carriers, which are chiral, helical and have a linear
E(k) dependence lead to many interesting physical phenomena such as chiral anomaly [1], extremely large positive magnetoresistance [2, 3, 4], or the planar Hall effect [1, 5]. The most commonly used methods to obtain MoTe
2 layers, beside exfoliation from natural crystals [6] are the flux method [3, 4, 7] and chemical vapour transport [8]. Currently, Molecular Beam Epitaxy (MBE) technique comes into play [9, 10, 11, 12] giving the perspectives to combine different phases of MoTe
2 and to grow heterostructures and hybrid structures.
In this paper we present the results of structural, optical and transport investigations of MoTe
2 thin layers. The samples were prepared on Al
2O
3 and SI-GaAs [111B] substrates which both, at the appropriate growth temperature, allow us to obtain 2H and 1T’ polytypes of MoTe
2 (as evidenced with Raman scattering) as well as other phases, e.g. Mo
6Te
6. Controlling the growth conditions allows to modify sample morphologies from regular 2D planes, through 3D precipitations to nanowires as studied
in-situ with RHEED images, and
ex-situ by TEM and SEM microscopy. Transport measurement were performed on large, millimeter-size Hall bars with metal (Ti/Au or In) contacts deposited via shadow masks. The resistance of the samples was measured in the temperature range 300 K – 1.5 K revealing either an increase of the resistivity for semiconducting samples or a very weak temperature dependence, showing significant disorder for the samples with the metallic phases. In the latter case, for high concentation (n
~ 1●10
16 cm
-2) several monolayer sample, the low value of carrier mobility (2 cm
2/Vs) and a linear magnetoresistance up to 12 T revealed sample inhomogeneity. Furthermore, we have observed that the poor stability of the MoTe
2 layers can be improved by different capping layers.
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* corresponding author:
[email protected]This research was supported by
NCN Opus 2017/27/B/ST5/02284