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Two-dimensional layered transition metal dichalcogenides (TMDCs) offer the ideal platform to optically initialize the qubits utilizing the superposition of valley polarized photons. However, in the commonly available 2H phase TMDCs, thickness sensitive crystal inversion symmetry demands the precise control over the number of layers, which makes the study of valley physics challenging. On the other hand, 3R-polymorphic phase TMDCs are non-centrosymmetric irrespective of the number of layers and therefore retain valley degree of freedom for all the thicknesses. Here, using polarization resolved photoluminescence measurements under linearly polarized excitations, we demonstrate the coherent superposition of the valley photons (known as valley coherence) in synthetic 3R-phase MoS2 with different numbers of layers ranging from 3 layers to 11 layers. With near-resonant excitation (633 nm for AX0), the degree of linear polarization (a measure of the valley coherence) is observed up to 70% at 80 K measurement temperatures and is found to be layer thickness independent. Robust valley coherence is attributed to the high optical quality and the 3R crystal symmetry of the MoS2. Using angle resolved polarization dependent measurements, it is established that the net dipolar emission aligns with the polarization orientations of the incident laser, which signifies the valley coherence to be independent of the crystal orientation. This study paves the way toward using 3R-phase MoS2 as a key material for the development of future quantum technologies utilizing valley polarized photons. [ABSTRACT FROM AUTHOR]

Integration of the emerging layered materials with the existing CMOS platform is a promising solution to enhance the performance and functionalities of the future CMOS based integrated circuits. In this direction, we have experimentally studied the suitability of the layered semimetals, namely, Td-WTe2, 1T′-MoTe2, 1T-PtTe2, and 1T-PtSe2, as an electrode with two most commonly used semiconductors, i.e., silicon (Si) and germanium (Ge) used in the CMOS technology. Two kinds of devices, i.e., metal–oxide–semiconductor (MOS) capacitors and metal-semiconductor (MS) diodes, are investigated with these semimetals as a conducting electrode. Through detailed electrical and physical characterizations, it is established that these semimetals form excellent interface with the underneath dielectric (SiO2) in the MOS structure and with the semiconductor (Ge) in the MS diode. Near ideal CV curves of MOS devices and large ON-current in the MS diodes signify that these semimetals act perfectly well as a contact electrode. Reduction in the Schottky barrier height of the MS diodes with decreasing values of the semimetal WF suggests the excellent interface of these semimetals with the Ge substrate. Most importantly, these semimetals do not add any unwanted series resistance across the current conduction path in the diode. Guided by these experimental observations, we propose that these semimetals can indeed be integrated with conventional CMOS platform, thus paving a way for an era of CMOS based heterogeneous electronics. [ABSTRACT FROM AUTHOR]

The work function (WF) of a material governs the back and forth movement of the charge carriers across the hetero-interface of two materials. Therefore, for optimum device performance, precise knowledge of the WF is prerequisite while employing any new material in electronic devices. In this work, using metal oxide semiconductor capacitors, we experimentally determine the WF of layered van der Waals topological semimetals (TSMs) 1T′-MoTe2, 1T-PtSe2, and Td-WTe2 as 4.87, 5.05, and 4.82 eV, respectively. The experimentally obtained results are corroborated with density functional theory calculations. Furthermore, by analyzing the vertical current transport across the metal oxide semiconductor stack using Fowler–Nordheim tunneling formalism, the barrier height between the TSMs and the gate insulator (SiO2) is experimentally calculated. The obtained barrier heights are also following the same trend as that of WF for three TSMs. These TSMs host unique topological nontrivial phases potentially useful for the development of emerging quantum technologies, and therefore, the findings of this study are significant for designing the future quantum devices. [ABSTRACT FROM AUTHOR]