The possibility of tailoring physical properties by changing the number of layers in van der Waals crystals is one of the driving forces behind the emergence of two-dimensional materials. One example ...is bulk MoS
, which changes from an indirect gap semiconductor to a direct bandgap semiconductor in the monolayer form. Here, we show a much bigger tuning range with a complete switching from a metal to a semiconductor in atomically thin PtSe
as its thickness is reduced. Crystals with a thickness of ~13 nm show metallic behavior with a contact resistance as low as 70 Ω·µm. As they are thinned down to 2.5 nm and below, we observe semiconducting behavior. In such thin crystals, we demonstrate ambipolar transport with a bandgap smaller than 2.2 eV and an on/off ratio of ~10
. Our results demonstrate that PtSe
possesses an unusual behavior among 2D materials, enabling novel applications in nano and optoelectronics.
Abstract
Atomic-scale disorder in two-dimensional transition metal dichalcogenides is often accompanied by local magnetic moments, which can conceivably induce long-range magnetic ordering into ...intrinsically non-magnetic materials. Here, we demonstrate the signature of long-range magnetic orderings in defective mono- and bi-layer semiconducting PtSe
2
by performing magnetoresistance measurements under both lateral and vertical measurement configurations. As the material is thinned down from bi- to mono-layer thickness, we observe a ferromagnetic-to-antiferromagnetic crossover, a behavior which is opposite to the one observed in the prototypical 2D magnet CrI
3
. Our first-principles calculations, supported by aberration-corrected transmission electron microscopy imaging of point defects, associate this transition to the interplay between the defect-induced magnetism and the interlayer interactions in PtSe
2
. Furthermore, we show that graphene can be effectively used to probe the magnetization of adjacent semiconducting PtSe
2
. Our findings in an ultimately scaled monolayer system lay the foundation for atom-by-atom engineering of magnetism in otherwise non-magnetic 2D materials.
High-speed, long-wavelength, telecom and datacom 10 Gb/s and 25 Gb/s avalanche photodiodes (APDs) are sensitive to excessive optical input power. We explain this failure mechanism and demonstrate an ...optimized device structure reaching over +6 dBm optical damage threshold and verify it by testing in volume production.
This paper reviews recent advances and novel applications of state-of-the-art III-V avalanche photodiodes. We demonstrate a record sensitivity of -34.5 dBm and -27 dBm, for 10 Gb/s and 25 Gb/s APDs ...respectively, with a high optical damage threshold above +6 dBm.
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