Two-dimensional Tellurium: Material Characterizations, Electronic Applications and Quantum Transport

Since the debut of graphene, many 2D materials have emerged as promising candidates for silicon alternatives to extend Moore’s Law, such as MoS₂ and phosphorene. However, some common shortcomings such as low mobility, instability and lack of massive production methods limit the exploration and applications of these materials. Here, we introduce a novel member to the 2D category – high-mobility air-stable 2D tellurium film (tellurene).

Tellurium (Te) is a narrow bandgap semiconductor with unique one-dimensional chiral structure. Recently, a hydrothermal synthesizing method was developed to produce large-area tellurene nanofilms with thickness ranging from tens of nanometers down to few layers. In this thesis, a thorough investigation of Te properties in 2D quantum region was first carried out by various material characterization techniques including TEM and Raman spectroscopy. Potential applications of Te-based electronics, optoelectronic and thermoelectric devices were explored, and high-performance Te FETs were achieved with record-high drive current over 1 A/mm via device scaling and contact engineering. Magneto-transport, including weak anti-localization and Shubnikov-de-Haas oscillations was studied at cryogenic temperature. Quantum Hall effect was observed for the first time in both 2D electron and hole gases with mobility of 6,000 and 3,000 cm²/Vs, and non-trivial Berry phase in Te 2D electron system was detected as the first experimental evidence of massive Weyl fermions. This work not only demonstrates the great potential of tellurene films for electronics and quantum device applications, but also expands the spectrum of topological matters into a new material species - Weyl semiconductors.