Challenges and opportunities in 2D heterostructures for electronic and optoelectronic devices

Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and their heterojunctions are prospective materials for future electronics, optoelectronics, and quantum technologies. Assembling different 2D layers offers unique ways to control optical, electrical, thermal, magnetic, and topological phenomena. Controlled fabrications of electronic grade 2D heterojunctions are of paramount importance. Here, we enlist novel and scalable strategies to fabricate 2D vertical and lateral heterojunctions, consisting of semiconductors, metals, and/or semimetals. Critical issues that need to be addressed are the device-to-device variations, reliability, stability, and performances of 2D heterostructures in electronic and optoelectronic applications. Also, stacking order-dependent formation of moir\ue9 excitons in 2D heterostructures are emerging with exotic physics and new opportunities. Furthermore, the realization of 2D heterojunction-based novel devices, including excitonic and valleytronic transistors, demands more extensive research efforts for real-world applications. We also outline emergent phenomena in 2D heterojunctions central to nanoelectronics, optoelectronics, spintronics, and energy applications

Two-dimensional III-VIA semiconductors and their applications in optoelectronic devices

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 04-12-202

Silicon-basedI nanostructures: Growth and Characterizations of Si2Te3 nanowires and nanoplates

Silicon-basedI nanostructures: Growth and Characterizations of Si2Te3 nanowires and nanoplate

Atomic and electronic structure of random and ordered 2D alloys

Recently, transition metal dichalcogenides (TMDs) have attracted increasing research interest as promising two-dimensional materials for a range of electronic and optoelectronic applications and for the fundamental science that can be studied in them. This interest stretches beyond the properties of pure TMD materials, with an increasing number of reports on doped-TMD and TMD alloys to increase the functionality of these materials. For example, by substituting or alloying the metals or chalcogens of the TMDs, it is possible to tune their electronic structure. In this thesis, single crystals of pure TMDs and of TMD alloys have been synthesised via chemical vapor transport (CVT). Techniques for the fabrication of van der Waals stacks with artificial sequences have been developed, specifically to allow the direct measurement of atomic and electronic structure in the alloys and to correlate these properties to optical spectroscopy measurements. The atomic structure of Mo1-xWxS2 alloys are visualised by annular dark field (ADF) scanning transmission electron microscopy (STEM). Statistical analysis of the images allows the atomic distributions to be compared to those from Monte Carlo simulations and first principles calculations. Mo1-xWxS2 alloys show random distributions as expected from thermodynamic considerations. The evolution of the band structure of the Mo1-xWxS2 alloys is determined by angle-resolved photoemission spectroscopy (ARPES) measurements and compared to first principles calculations. Combined, these results demonstrate that TMD alloying is a powerful approach for band structure engineering. In contrast to the Mo1-xWxS2 alloys, short-range ordering is found in Nb0.1W0.9S2, with the Nb atoms forming atomic lines along one of the equivalent crystallographic directions. This ordering is confirmed by quantitative statistical analysis through the Warren-Cowley short-range order (SRO) parameters. Meanwhile, density function theory (DFT) calculations have been applied to explain this ordering, revealing this structure results from a combination of thermodynamic and kinetic considerations