First Principle Investigation On Intrinsic Mobility Of ?-graphyne,BC₃ And C₃N 2D Semiconductors And Perovskite

Mobility is an important physical parameter to describe the conductivity of carriers in semiconductors.It reflects moving speed of carriers under electric field,and determines the efficiency of semiconductor electronic devices such as field effect transistors,solar cells and light-emitting diodes.High mobility can improve the response speed of the device and reduce the power consumption.It is difficult to determine the intrinsic mobility experimentally for novel semiconductors due to impurities and defects in the measured samples.It is important to identify the ultimate theoretically achievable carrier mobility,so as to set out clear guidelines for the application of these materials.In this paper,the mobility of some novel semiconductors is predicted by empirical models and Boltzmann transport equation,and the main scattering mechanism is revealed.The specific contents are as follows:(1)Investigation on electrical transport properties for y-graphyne.As a novel graphene-like allotropes,y-graphyne opens the band gap and realizes the characteristics of semiconductor.Firstly,the biaxial strain behavior is investiaged and strain range is predicted.Ab initio molecular dynamics verifies its thermodynamic stability,and the fracture mechanism under biaxial strain is analyzed.Then,longitudinal acoustic phonon model and optical phonon model are used to calculate carrier mobility.The rationality of these empirical models is discussed.The contribution of acoustic and optical phonons to mobility is revealed.Finally,using Boltzmann transport equation,considering all electron-phonon interaction,its room temperature mobility is predicted.(2)Investigation on electrical transport properties for BC3 and C3N 2D semiconductors.Boron and nitrogen are the nearest neighbor elements of carbon.They can replace the C atom in graphene to synthesize 2D semiconductors of BC3 and C3N.Firstly,the equivalent conduction band minimum and valence band maximum in the whole Brillouin region are determined.The effective mass of light,heavy holes and electrons is calculated.Then,longitudinal acoustic and optical phonon models are used to investigate carrier mobility.The contribution of equivalence points,light/heavy holes and electrons to mobility is considered,and the rationality of the deformation potential model is discussed.Finally,the Boltzmann transport equation is used to predict their carrier mobility.The mobility of BC3 and C3N is compared with other 2D materials,and the factors limiting the mobility are revealed.(3)Investigation on electrical transport properties for bulk perovskite.The structural stability and mobility of perovskite CsSnI3 and CsPbI3 are systematically investigated.Firstly,the structural stability of their perovskite phases(cubic,tetragonal,orthogonal)and non perovskite phase are analyzed.Their effective mass is calculated by constant energy surfaces.The relationship between phase stability and carrier transport characteristics is revealed.Then,the longitudinal acoustic phonon model and the polar optical phonon model are used to calculate the mobility.The scattering from acoustic phonons and optical phonons is investigated.Perovskite as a polar semiconductor,the longitudinal optical phonon causes a macroscopic electric field in the system,and its scattering is revealed.Finally,using Boltzmann transport equation under relaxation time approximation,their possible mobility is predicted.(4)Investigation on electrical transport properties for 2D perovskite.Firstly,the biaxial strain behavior of monolayer hybrid perovskite(C4H9NH3)3GeI4 and(C4H9NH3)2SnI4 is investigated,and their strain range is discussed.Under biaxial strain,the bond change process in inorganic atomic layer is analyzed.Ab initio molecular dynamics verifies their thermodynamic stability.Then,the longitudinal acoustic phonon model is used to calculate the carrier mobility.The effective mass,elastic modulus and deformation potential are calculated.The contribution of organic molecules to elastic modulus is revealed.Finally,the optical phonon model is used to calculate mobility.The deformation potential constant for branch optical phonon is analyzed.The contribution of acoustic and optical phonon to mobility is investigated.The total mobility is predicted and the physical mechanism limiting their mobility is revealed.