Modualtion Of Opticaland Electronic Properties Based On Two-Dimensional Ca?OH?₂ And ?-tellurene

Since the graphene was fabricated,two-dimensional?2D?materials have received much attention due to the novel properties far from their bulk forms.Graphene possesses high carrier mobility and excellent optical conductivity and mechanical properties far beyond graphite.To meet the demend for electronic applications,thands of 2D materials have been fabricated.2D materials reprented by transition-metal dichalcogenides and black phosphorus have triggered the upsurge of 2D materials research.Here,we focus on the 2D X?OH?₂?X=Ca,Mg?and?-tellurene and their tunable electronic and optical properties.2D X?OH?₂?X=Ca,Mg?possesses the direct band structures with band gap about 3.68eV.However,it shows poor optical absorption,which needs to be improved.2D?-tellurene is resently fabricated and possesses layer-dependent band gap.2D?-tellurene possesses direct band structures and lower exciton binding energy with strong oscillator strength?¹0⁴?,indicating high electron-hole recombination rate.In this thesis,the electronic and optical properties for 2D X?OH?₂?X=Ca,Mg?/Graphene,Ca?OH?₂/?-MoTe₂,Graphene/?-tellurene and?-tellurene were studied by using the first principle methods.The results are discussed as follows:1)2D X?OH?₂?X=Ca,Mg?/Graphene possesses low p-type Schottky barriers?>0.3eV?.Applying external electric fields can easily change Schottky to Ohmic contact and realize effectively carriers injection.Moreover,we find that X?OH?₂?X=Ca,Mg?/Graphene/Graphene holds lower p-type Schottky barriers with respect to X?OH?₂?X=Ca,Mg?/Graphene.Furthermore,the lower Schottky barrier heights can be more easily tuned to zero.This study provide possibility for 2D X?OH?₂?X=Ca,Mg?/Graphene in the application of electronic devices.2)Ca?OH?₂/?-MoTe₂ possesses type-I band alignment with electrons and holes being confined in the?-MoTe₂ when excited.Furthermore,it has high optical absorption(¹0⁵ cm^-1).The type-II band alignment can be achieved at the effects of external electric fields.3)For Graphene/?-tellurene,we find that the stable heterostructures can be formed between graphene and?-tellurene.Meanwhile,p-type doping can be found in graphene,which can be tuned to n-type doping by interlayer coupling effects and applying external electric fields.Moreover,the Schottky barrier heights can be controlled by altering interlayer distance or external electric fields.4)?-tellurene is a newly found 2D semiconductors,which comes from the bulk materials Te.?-tellurene possesses weakly bound excitons with binding energy less than 0.18eV.And?-tellurene has high oscillator strength of 10⁴in the spectra range of 1-2eV,implying high electron-hole combination rate.Moreover,applying in-plane strain or increasing thickness can make the first exciton peaks occur red-shift.This study real the physical nature of excitons in?-tellurene and pave the way to the optoelectronics.