Pressure Effect On Self-trapping Energies Of Polarons

In this thesis, the pressure effect on the electron-phonon (e-p) interaction and the self-trapping energies of polarons in polar semiconductor quantum wells(QWs) with finite barriers are discussed by considering the influence of three branches of optical phonon modes. Furthermore, the properties of polarons in polar crystals are investigated by taking account of the influence of pressure effect and the electrons emitting or absorbing many virtual phonons.For QWs, a modified LLP variational method is adopted to calculate the polaron self-trapping energies by considering the finite barrier and pressure effect. The influences of the e-p interaction and three branches of optical phonon modes (including the confined longitudinal optical (LO) phonons, the half space LO phonons and interface optical (10) phonons) are considered. The influences of optical phonon modes on polaron self-trapping energies as functions of well width are given respectively. The numerical results show, for Al_xGa_1-xAs/GaAs QWs, that the interaction energies between an electron and phonon modes play different roles as the well width varying. The half space LO phonons is important for narrow wells, in contrasts, the contribution from the confined LO phonons is remarkable for wide wells, whereas, the contribution from the 10 phonons is significant for wells with media width. The e-p interaction energies and polaron self-trapping energies increase as pressure.For polar crystals, an improved linear combination operator method is used to investigate the properties of polarons by considering the influence of electrons emitting or absorbing many virtual phonons. The numerical calculation is given to show the relations among the polaronic self-trapping energy, e-p coupling constants, effective masses of polarons, average virtual phonon number around electrons and pressure in the case of intermediate coupling. It is found from the results of â…¢-â…¤ group GaAs and â…¡-â…¥ group ZnSe that the pressure effect on â…¡-â…¥ group materials is relativelymore obvious than that on III-V group materials.