By employing the two-parameter variational approach, the donor-impurity states with surface optical (SO) phonons, also called SO phonon bound polarons in a quasi-one-dimensional (Q1D) wurtzite nanowire (NW) are investigated. Numerical calculations on a GaN NW are performed. The results reveal that the SO phonon contribution to the binding energy of the SO phonon bound polaron in GaN NWs reaches 200 meV, which is one order of magnitude larger than that of GaAs NWs with the same radius. The large contribution of SO phonons to the total binding energy is mainly ascribed to the stronger electron-phonon coupling constant in GaN materials. The calculated results of impurity binding energy are consistent with the recent experimental measurement of the active energy in GaN NW systems. The numerical results also shows that the two-parameter variational approach is necessary and suitable for the description of donor-impurity states in Q1D wurtzite GaN NW structures, especial for the NWs with a relatively small radius (such as R < 10 nm).
The influence of crystal structure on the phonon modes and electron–phonon coupling properties in nitride quantum ring (QR) structures is investigated based on the macroscopic dielectric continuum model. It is found that three types of phonon modes including the surface optical (SO) phonon modes, the exact confined (EC) modes, and quasiconfined (QC) modes can coexist in the wurtzite nitride QR. However, only the SO modes and EC modes may appear in zinc‐blende nitride QR, and the QC modes cannot exist in zinc‐blende QRs in general. Numerical calculation on AlN QR shows that the SO modes of zinc‐blende QR are more dispersive than those of wurtzite QR. Furthermore, the degenerative behavior of QC modes to SO modes in wurtzite QRs is clearly observed. Moreover, the electron–phonon coupling functions in zinc‐blende QRs are larger than those in wurtzite QRs. These results reveal that the crystal structures greatly affect not only the type of phonon mode, but also the coupling strength of electron–phonon interaction. The present theoretical scheme and the numerical results are quite useful and important for further understanding and investigating the polaronic effect and related physical properties in wurtzite and zinc‐blende nitride QRs.
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