Study On Electronic Properties Of GaN/MoS₂ Heterojunction

Since graphene was separated from graphite in 2004,it has stimulated global research enthusiasm because of its perfect electronic structure and unique properties.However,the bandgap of pristine graphene is zero,which greatly limits its practical applicationss in many fields such as optoelectronic devices.In recent years,transition metal dichaldogenide,such as molybdenum disulfide?MoS₂?and tungsten disulfide?WS₂?,have become ideal channel materials for electronic and optoelectronic devices with high performance and low static power by virtue of their suitable natural bandgap and carrier mobility.Moreover,the surface of two-dimensional?2D?materials has no dangling bonds and interacts with other materials through van der Waals?vd W?force.Therefore,2D materials and other materials of different dimensions can be integrated through non-covalent interaction,which will greatly expand the research scope and applications of vd W heterojunctions.The work of this paper mainly includes theoretical research on the electronic structure and properties of pristine monolayer MoS₂ and electronic properties of GaN/MoS₂ heterojunction.The main results and innovations are summarized as follows:?1?The electronic structure of pristine monolayer 2H-MoS₂ is analyzed by using the first principles calculation.Simultaneously,by calculating its absorption coefficient,reflective index,refractive index and extinction coefficient,the optical properties of monolayer MoS₂ are analyzed systematically.The results show that monolayer MoS₂ has obvious absorption properties in visible and ultraviolet light range.The maximum absorption peak appears at 13.2 e V,which indicates that monolayer MoS₂ has strong absorption capacity for ultraviolet light.Therefore,it has application prospects in ultraviolet detection.The reflective index and refractive index curves indicate that monolayer MoS₂ reflects weakly to visible light?1.6 e V?2.5 e V?,which theoretically verifies that monolayer MoS₂ film observed in experiments is transparent.?2?Establish monolayer MoS₂ nano device models in Zigzag and Armchair direction.Electronic transport properties of MoS₂ nano device can be analyzed by calculating its electronic transmission coefficient.The results indicate that the conductive ability of nano devices in the Zigzag direction is stronger than that in the Armchair direction.?3?Propose a new method that can directly measure the local mobility of MoS₂ on semiconductor substrates.By using atomic force microscope?AFM?,Kelvin probe force microscope?KPFM?,conductive probe atomic force microscope?C-AFM?,and combining with the energy band diagram of the heterojunction,the local mobility of MoS₂ on the GaN substrate can be calculated.Specifically,the carrier density and barrier height of semiconductor/MoS₂ heterojunction can be obtained from the KPFM measurements and its energy band diagram.The I-V characteristics of the heterojunction can be measured by C-AFM and the effective contact area between AFM tip and MoS₂ film can be obtained.Then,the mean free path of carrier and the local mobility of MoS₂ on the semiconductor substrates can be figured out.By using this method,the local mobility of bilayer MoS₂ on GaN substrate can be figured out,which is about 10.5 cm²V^-1s^-1.Simultaneously,the scattering mechanism which limits the transmission properties of MoS₂ on semiconductors at room temperature is given.