Pressure And Polaron Effect On The Binding Energies Of Impurity States In Wurtzite Nitrides Semiconductor

In this thesis, the impurity states in wurtzite crystal structure are investigated byconsidering the influence of uniaxial anisotropy and polaron effect. A variationalmethod is adopted to discuss shallow impurity states binding energies in the effectivemasses approximation by considering the variations of effective masses of an electron,dielectric constants and crystal lattice vibration frequencies with hydrostatic pressure.The numerical calculation is performed for the binding energies of impurity states inGaN,AlN and InN crystal. The relations between the binding energies of shallowimpurity states and structure anisotropy angle are given. The result indicates that theuniaxial anisotropy of structure on the binding energies of impurity states is obvious.The binding energies increase with pressure.The effect of uniaxial anisotropy on the binding energies was calculated firstly.The numerical results show that the binding energies of impurity states increase withstructure anisotropy angle monotonically. The maximum value is achieved in thedirection perpendicular to the main axis. Compared with the zinc blend (isotropy) structure, the binding energies in GaN and AlN materials with the impurity states inthe main axis direction below the isotropy structure, in the direction perpendicular tothe main axis than the isotropy structure, and InN material impurities state bindingenergy is still lower than the zinc blend structure. It is found that the binding energyanisotropy effects mainly from the anisotropy of the dielectric constants. Furthermore,a modified LLP variational method is adopted to discuss the polaron effect on thebinding energy of an impurity in bulk nitride semiconductor by considering thepressure effect. The influences from two optical phonon modes in the wurtzite crystalstructure (LO-like phonon and TO-like phonon) on the binding energy are considered.The results show that the polaron effect obviously decreases the binding energy, butpressure weakens the polaron effect. It indicates that the impurity states-LO-likephonon interaction influences on the polaron effect are dominant.