Research On Gate-Controlled Behaviours Of Two-Dimensional Electronic Devices Based On Layered Functional Material Heterojunction

With the rise of graphene,two-dimensional materials have triggered broad investigations.The exploration of novel 2D materials and the discovery of novel physical properties have been driving the development of the entire 2D materials field,which has important scientific significance in frontier physics,device applications,and materials science.In this dissertation,two-dimensional nanomaterials GaTe and CrOCl are studied from the aspects of controllable synthesis,preparation of van der Waals heterostructure electrical devices,and electrical transport properties.Two-dimensional GaTe has a 1.6 eV p-type direct bandgap,which leads it to possessing a large light absorption coefficient.It is known that GaTe has a layered structure with monoclinic system.Due to in-plane low-symmetry,GaTe exhibits anisotropy.Experimentally,GaTe transistors encapsulated in h-BN with few electrodes were fabricated.Few-layered GaTe exhibits giant anisotropic resistance,which can be further tuned by the gate voltage.Electrical conductivity along different directions can be gate tuned from a ratio of less than one order to as large as 103.The Raman intensity of twodimensional GaTe were investigated by firstprinciples calculations based on the density functional theory,it is known that y axis of GaTe layer corresponds to a maximum conductivity.To unveil the origin of the anisotropy of in-plane electrical conductivity found in ultra-thin GaTe,we performed first-principles electronic structure calculations and non-equilibrium Green’s functional quantum transport modeling on GaTe monolayer.Graphene,a two-dimensional sheet of sp2-hybridized carbon material,possesses excellent properties.Theoretical studies on graphene in proximity with magnetic insulators have revealed novel correlated phenomena,such as quantum anomalous Hall gaps.In this work,monolayered graphene as well as thin CrOCl flakes and encapsulating hexagonal boron nitride(h-BN)flakes were exfoliated from high-quality bulk crystals and stacked in ambient condition using the dry transfer method.The vertically assembled van der Waals heterostructures were then patterned into Hall bars with their electrodes edge-contacted.At finite magnetic fields,Landau fans in them are found to be asymmetric with respect to the presumed charge neutrality point,with the transition from a fan-like diagram in the hole side to a cascades-like diagram in the electron side.This is a strong indication that a peculiar charge transfer is taking place at the interface of CrOCl and graphene.Quantum Hall effect(QHE)has been the ground to construct modern conceptual electronic systems with emerging physics including topological superconductor and quantum information processing.Here we demonstrate the observation of an unusual QHE,which differs markedly from the known picture,in graphene samples in contact with an anti-ferromagnetic insulator CrOCl equipped with dual gates.In the D-B space,unlike the conventional D-independent ones,LLs in the CT-QHE phase exhibit parabolic dependence between B and D.Landau quantization can start from as low as sub 100 mT and prevails up to 100 K in a wide gate.