PTMCnano · Post-transition metal chalcogenides: 2D nanoelectronics and photonics

Post-transition metal chalcogenides: 2D nanoelectronics and photonics

The family of two-dimensional (2D) crystals encompasses materials from insulators and semiconductors to superconductors, and is rapidly expanding. Such crystals can be visualized as a single molecular plane peeled off of a layered bulk (3D) crystal. Stacking layers of different 2D materials on top of each is similar in effect to the molecular beam epitaxy used to produce the highest quality semiconductor devices, but much more versatile: such multilayer heterostructures are easier to fabricate, and there is a huge number of potential combinations. Since 2D heterostructures may have exciting new properties that are completely different from those of the parent materials, they will likely revolutionalize the semiconductor industry in the following decades. Recent results on a subgroup of this family, post-transition metal chalcogenides (PTMCs), like indium or gallium selenide (InSe, GaSe), suggest that transistors and more advanced nanodevices of exceptional electronic quality can be fabricated of these materials. Moreover, they are excellent candidates for photodetectors, LEDs, and other photonic applications. The main objectives of the project were the following: 1. Fabricate and electrically characterize PTMC transistors, in order to find the best methods for fabrication, including combinations with other 2D crystals. 2. By using so-called gate electrodes over the surface of a PTMC layer, electrostatically trap electrons to quasi isolated islands called quantum dots (QDs). These can potentially be exploited to create quantum bits for quantum computers. Since no QDs have been made of PTMCs before, it is important to understand their electronic transport characteristics, to determine their viability as quantum bits. 3. Fabricate PTMC devices for optical applications. Conclusions: During the action, several PTMC transistors have been fabricated and electrically characterized. Of these, indium selenide (InSe)-based devices showed the greatest promise. Many devices included top gates: with these, quasi one dimensional conducting channels have been successfully defined, and conductance quantization has been observed, indicating their outstanding quality. Single quantum dots have also been created in InSe for the first time. Working light emitting diodes (LEDs) have also been fabricated. However, sample quality was sometimes inadequate, likely due to surface contamination. Therefore, a technique has been developed to stack 2D layers on each other in total vacuum: measurements on the first transistors indicate high quality, showing that this is a promising way forward.

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