UC Irvine

Two-dimensional (2D) semiconductors, such as the transition metal dichalcogenides(TMDs) are emergent materials in which the valley and spin degrees of freedom are strongly coupled, making them promising candidates for next-generation quantum devices. Monolayer MoTe₂ is distinctive within this family as the narrowest-gap Mo-based TMD, with a near-infrared optical gap close to that of silicon and boasting large spin-orbit coupling. However, its intrinsic electrical properties are difficult to access. Depositing a three-dimensional metal onto a 2D semiconductor produces a Schottky barrier at the interface. Contacts that appear acceptable at room temperature become highly resistive upon cooling. Thus, achieving Ohmic contacts at cryogenic temperatures is challenging and has hindered the study of their intrinsic electrical properties. This dissertation addresses that obstacle through contact and interface engineering and uses the resulting device platform to measure the intrinsic optical and electronic properties of monolayer 2H-MoTe₂. Bulk single crystals are grown by the tellurium-flux method, mechanically exfoliated, and assembled into hexagonal boron nitride encapsulated heterostructures entirely within an argon-filled glovebox, so that the air-sensitive interfaces that govern both contact quality and optical response are preserved. By creating low-contact resistance interfaces, we successfully measured the magnetoresistance of MoTe2 under varying magnetic fields (B) and temperatures (T). Our results show clear Shubnikov-de Haas (SdH) oscillations at magnetic fields above 2.3T, indicating a high carrier mobility of approximately 4,350 cm²/V·s. Additionally, we observed a splitting of the SdH oscillations for B > 7T, which is a manifestation of the large Zeeman splitting. This splitting is corroborated by a simulated Landau fan diagram, suggesting a Landé g-factor of 10.8. We performed separate optical measurements on our flux grown 2H-MoTe2 without RuCl3 to study exciton energies in our high-quality monolayers. Excitons, or bound electron-hole pairs, play a crucial role in the optical response of monolayer 2H-phase transition-metal dichalcogenides (TMDs). They hold significant promise for the development of novel quantum opto-electronic devices due to their large binding energies and strong spin-orbit coupling. Here, we report the experimental observation of NIR Rydberg excitons and conduction band-split charged excitons, in high-quality, boron nitride (BN)-encapsulated monolayer MoTe2 devices, probed by photoluminescence and electroluminescence spectroscopy. By employing a graphite bottom gate, we successfully modulate the emission intensity of various excitonic species. Additionally, our device fabrication process within an argon-filled glove box ensures clean TMD/metal electrode interfaces, enabling the construction of p-n junctions near the electrodes. Our work significantly advances our understanding of excitons in monolayer TMDs and contributes to the application of MoTe2 in NIR quantum opto-electronic devices. Together, these results establish contact and interface engineering as an enabling step for intrinsic measurements of monolayer 2H MoTe₂ and show that a single silicon-compatible platform supports both near-infrared excitonic light emission and high-mobility, spin-valley- resolved quantum transport.